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Home My WebLink AboutLAKEVIEW SUBDIVISION - FDP - FDP130047 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL REPORT LAKEVIEW SUBDIVISION Fort Collins, Colorado November 21, 2013 Prepared for: Century Communities, LLC 8390 E. Crescent Parkway, Suite 650 Greenwood Village, CO 80111 Prepared by: 200 South College Avenue, Suite 100 Fort Collins, Colorado 80524 Phone: 970.221.4158 Fax: 970.221.4159 www.northernengineering.com Project Number: 665-002  This Drainage Report is consciously provided as a PDF. Please consider the environment before printing this document in its entirety. When a hard copy is absolutely necessary, we recommend double-sided printing. ADDRESS: 200 S. College Ave. Suite 10 Fort Collins, CO 80524 PHONE: 970.221.4158 FAX: 970.221.4159 WEBSITE: www.northernengineering.com November 21, 2012 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Final Drainage and Erosion Control Report for Lakeview Subdivision Dear Staff: Northern Engineering is pleased to submit this Final Drainage and Erosion Control Report for your review. This report accompanies the 11.21.13 Final Development Plan submittal for the proposed Lakeview Subdivision Single-family development. Comments from the Preliminary Development Plan Review Letter dated 09.20.13 have been addressed. Written responses thereto can be found in the comprehensive response to comments letter on file with Current Planning. This report has been prepared in accordance to Fort Collins Stormwater Criteria Manual (FCSCM), and serves to document the stormwater impacts associated with the proposed Lakeview Subdivision project. We understand that review by the City is to assure general compliance with standardized criteria contained in the FCSCM. If you should have any questions as you review this report, please feel free to contact us. Sincerely, NORTHERN ENGINEERING SERVICES, INC. Ryan O. Banning, PE Project Engineer Lakeview Subdivision Preliminary Drainage Report TABLE OF CONTENTS I. GENERAL LOCATION AND DESCRIPTION .................................................................... 1 A. Location ..................................................................................................................... 1 B. Description of Property ................................................................................................ 2 C. Floodplain .................................................................................................................. 4 II. DRAINAGE BASINS AND SUB-BASINS ........................................................................ 4 A. Major Basin Description ............................................................................................... 4 B. Sub-Basin Description ................................................................................................. 4 III. DRAINAGE DESIGN CRITERIA .................................................................................... 5 A. Regulations ................................................................................................................ 5 B. Four Step Process ....................................................................................................... 5 C. Development Criteria Reference and Constraints ............................................................. 6 D. Hydrological Criteria .................................................................................................... 7 E. Hydraulic Criteria ........................................................................................................ 7 F. Floodplain Regulations Compliance ............................................................................... 8 G. Modifications of Criteria ............................................................................................... 8 IV. DRAINAGE FACILITY DESIGN ..................................................................................... 8 A. General Concept ......................................................................................................... 8 B. Specific Details ......................................................................................................... 10 V. CONCLUSIONS ........................................................................................................ 12 A. Compliance with Standards ........................................................................................ 12 B. Drainage Concept ...................................................................................................... 12 References ......................................................................................................................... 13 APPENDICES: APPENDIX A – Hydrologic Computations APPENDIX B – Hydraulic Computations B.1 – Storm Sewers B.2 – Street Flow B.3 – Inlets B.4 – Detention Facilities APPENDIX C – Water Quality Design Computations APPENDIX D – Operations and Maintenance Guidelines for permanent BMPs APPENDIX E – Erosion Control Report Lakeview Subdivision Preliminary Drainage Report LIST OF TABLES AND FIGURES: Figure 1 – Aerial Photograph .................................................................................................. 2 Figure 2 – Proposed Site Plan ................................................................................................. 3 Figure 3 – Existing Floodplains ............................................................................................... 4 Table 1 – Detention Storage Summary ................................................................................... 11 MAP POCKET: C500 - Drainage Exhibit Lakeview Subdivision Final Drainage Report 1 I. GENERAL LOCATION AND DESCRIPTION A. Location 1. Vicinity Map 2. The Lakeview Subdivision project site is located in the northwest quarter of Section 30, Township 6 North, Range 68 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. 3. The project site is located on the south side of Drake Road, east of Christ Center Community Church (Church), and is bordered by single family residences on the south and east. The existing right-of-way (ROW) along Drake Road adjacent to the property is 90-feet. 4. The project site has an existing regional detention pond within the property located on the southern property boundary. Said pond provides detention for the existing Church property and will be upgraded with the proposed development to meet current City criteria and standards for the existing Church property and proposed development. A City of Fort Collins detention facility is located south of the subject property, and for reference, Williams Lake is located northwest of the subject property. Per the ALTA Land Title Survey prepared for the subject property by Northern Engineering (Northern) and dated July 26, 2011, no existing drainage easements are within the property. No public storm sewer is located immediately adjacent to the property. 5. Single family subdivisions are adjacent to the subject property including Silverwood Lakeview Subdivision Final Drainage Report 2 2nd Subdivision and Eldorado Springs 2nd Subdivision, which are both located east of the project site, and Eastborough Subdivision, which is located south of the project site. As previously noted, Drake Road borders the north property boundary, and the entire remainder of the site to the west is bounded by Christ Center Community Church property. B. Description of Property 1. The Lakeview Subdivision property is approximately 11.23 net acres. Figure 1 – Aerial Photograph 2. The subject property currently consists of athletic facilities including several soccer fields, a baseball diamond, and a single small maintenance building. As such, the ground cover generally consists of sod and some native seeding with numerous trees and shrubs located mainly at the perimeter of the property. Due to the current use, slopes are rather gentle throughout (i.e., 2±%). General topography slopes from north to the south towards the detention area at the south end of the property. 3. According to the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Soil Survey, the site consists of Stoneham loam and Nunn clay loam, which fall into Hydrologic Soil Groups B and C respectively. More site-specific exploration found varying materials including sandy clay with occasional sand layers and sandy gravel. See the Geotechnical Engineering Report by CTL Thompson (CTL Thompson Project No. FC05622-115) for additional information. Lakeview Subdivision Final Drainage Report 3 4. The proposed Lakeview Subdivision development project will develop the majority of the existing site, removing the existing athletic facilities and small maintenance building and sub-divide for 42 single-family residential lots. Existing landscaping north of the project will be maintained and common landscaping tracts will be provided. Figure 2– Proposed Site Plan 5. There are no irrigation ditches or related facilities in the project’s vicinity. 6. The proposed land use is residential, single-family dwellings. This is a permitted use Lakeview Subdivision Final Drainage Report 4 in the current Low Density Residential (R-L) Zoning. C. Floodplain 1. The subject property is not located in either a FEMA regulatory or City of Fort Collins designated floodplain. The nearest City designated floodplain is more than one-half mile from the subject property. 2. FEMA places the subject property within the Zone X Flood Hazard Area, which constitutes an area determined to be outside the 0.2% annual chance floodplain. Figure 3 – Existing Floodplains II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Description 1. The Lakeview Subdivision project is located within the City of Fort Collins’ Foothills Drainage Basin, which is within central Fort Collins and is to a large degree dominated by residential development. 2. A portion of the subdivided property is located within the City of Fort Collins’ Spring Creek Drainage Basin. The project is not modifying this portion of the property. B. Sub-Basin Description 1. The subject property historically drains overland towards the south and into the Lakeview Subdivision Final Drainage Report 5 existing detention facility located at the southern boundary of the property. The detention area outlets into a City of Fort Collins detention facility immediately south of the subject property. The Lakeview Subdivision development aims to preserve the existing drainage patterns as much as possible, and will maintain the same outfall location. A more detailed description of the project’s drainage patterns follows in Section IV.A.4., below. 2. The existing Church property to the west of the subject site drains via overland flows and channelized gutter flows to the existing drainage facility on the property. These off-site drainage flows and patterns will be maintained and accounted for with the proposed development. The project site does not drain across any off-site private land. III. DRAINAGE DESIGN CRITERIA A. Regulations There are no optional provisions outside of the FCSCM proposed with the Lakeview Subdivision project. B. Four Step Process The overall stormwater management strategy employed with the Lakeview Subdivision project utilizes the “Four Step Process” to minimize adverse impacts of urbanization on receiving waters. The following is a description of how the proposed development has incorporated each step. Step 1 – Employ Runoff Reduction Practices Several techniques have been utilized with the proposed development to facilitate the reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the current use as athletic facilities by implementing multiple Low Impact Development (LID) strategies including: Conserving existing amenities in the site including the existing vegetated areas and large trees around the perimeter of the site, particularly the north edge of the site adjacent to East Drake Road. Utilize minimum allowable grades across lots to reduce the rate of runoff from the properties and promote infiltration. Minimize the use of storm sewer as a conveyance to increase travel times and promote evaporation. Implement a network of drywells prior to pond outfall to promote infiltration. Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with Slow Release The efforts taken in Step 1 will facilitate the reduction of runoff; however, urban development of this intensity will still generate stormwater runoff that will require additional water quality measures to be implemented. All stormwater runoff from the site will ultimately be routed to the south where it is intercepted and treated in the main water quality and detention pond prior to leaving the site. A 40-hour release will be implemented for the WQCV to allow sedimentation and runoff treatment. Lakeview Subdivision Final Drainage Report 6 Step 3 – Stabilize Drainageways As stated in Section I.C, above, there are no major drainageways in or near the subject property. While this step may not seem applicable to The Lakeview Subdivision development, the proposed project indirectly helps achieve stabilized drainageways nonetheless. Currently, the existing site includes an undersized detention pond located where the proposed water quality and detention pond is being proposed. By providing additional detention volume, downstream drainageways are further protected during flood events. By providing water quality where none previously existed, sediment is removed prior to the downstream drainageway systems. Furthermore, this project will pay one-time stormwater development fees, as well as ongoing monthly stormwater utility fees, both of which help achieve City-wide drainageway stability. Step 4 – Implement Site Specific and Other Source Control BMPs. Within the pond and the storm system, several BMPs will be utilized as site specific permanent BMPS including: A Snout devise on inflow pipes to reduce oil loads from the existing parking area. A pre-forebay settling sump within the new inlet. A sediment forebay at each of the inlet to the pond to allow sediment to settle from the incoming stormwater runoff before being delivered to the main pond facility An interconnected network of drywells with surrounding bioretention media Natural bottom swales instead of pans to promote infiltration at the request of the City A micro pool with initial surcharge volume included in the outlet structure design. A water quality outlet with 40-hour release to allow for settling. C. Development Criteria Reference and Constraints 1. The subject property is part of the First Christian Planned Unit Development (PUD) dated 8/26/80, which provided the drainage study for the subject property. Within said study, drainage patterns and impervious areas (C-values) have been master planned for the ultimate developed condition of the subject property. It was with the First Christian PUD that the existing regional detention pond for the property was designed and installed. Note that from a recent topographic survey of the pond, it appears that the existing pond was not built per the original plans, and is currently undersized as the actual spill elevation of the pond is approximately 2.2-feet below the designed elevation. This study will conform, to the extent possible, to the concepts within the original drainage study performed with the First Christian PUD, including: Drainage patterns and detention pond location. Drainage basin designations. Detention pond release rate in order to limit the impact to downstream facilities. This study will also be updating several items within the original study including: Hydrology calculations utilizing the current City of Fort Collins Rainfall Intensity Data. Detention storage volume calculations based upon current City of Fort Collins criteria. The addition of water quality treatment for the entire First Christian PUD property. Lakeview Subdivision Final Drainage Report 7 2. There are no known drainage studies for any adjacent properties that will have any effect on the Lakeview Subdivision project. 3. The subject property is essentially an "in-fill" development project as the property is surrounded by currently developed properties. As such, several constraints have been identified during the course of this analysis that will impact the proposed drainage system including: Existing elevations along the east and south property lines adjacent to existing residential properties will be maintained. Existing elevations and vegetation on the north side of the subject property will be preserved. Except where prohibited, grades along the existing private drive on the west side of the subject property will be maintained. As previously mentioned, overall drainage patterns of the existing site will be maintained. Elevations of existing downstream facilities that the subject property will release to will be maintained. D. Hydrological Criteria 1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in Figure RA-16 of the FCSCM, serve as the source for all hydrologic computations associated with the Lakeview Subdivision development. Tabulated data contained in Table RA-7 has been utilized for Rational Method runoff calculations. 2. The Rational Method has been employed to compute stormwater runoff utilizing coefficients contained in Tables RO-11 and RO-12 of the FCSCM. 3. The Rational Formula-based Federal Aviation Administration (FAA) procedure has been utilized for initial detention storage calculations. EPA SWMM has been utilized for final detention storage calculations. 4. Three separate design storms have been utilized to address distinct drainage scenarios. A fourth design storm has also been computed for comparison purposes. The first design storm considered is the 80th percentile rain event, which has been employed to design the project’s water quality features. The second event analyzed is the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The third event considered is the “Major Storm,” which has a 100-year recurrence interval. The fourth storm computed, for comparison purposes only, is the 10-year event. 5. No other assumptions or calculation methods have been used with this development that are not referenced by current City of Fort Collins criteria. E. Hydraulic Criteria 1. As previously noted, the subject property historically drains to a separate detention facility located south of the property, which is owned and maintained by the City of Fort Collins. In order to maintain the current capacity of the downstream City of Fort Collins detention facility and associated storm sewers, the release rate from the proposed detention pond on the subject property will not increase from the rate originally designed with the First Christian PUD. 2. All drainage facilities proposed with the Lakeview Subdivision project are designed in accordance with criteria outlined in the FCSCM and/or the Urban Drainage and Flood Control District’s (UDFCD) Urban Storm Drainage Criteria Manual. Lakeview Subdivision Final Drainage Report 8 3. As stated in Section I.C.1, above, the subject property is not located in either a FEMA regulatory or a City of Fort Collins designated floodplain. 4. The Lakeview Subdivision project does not propose to modify any natural drainageways. F. Floodplain Regulations Compliance 1. As previously mentioned, this project is not subject to any floodplain regulations. However, extra care has been taken to ensure that neither existing nor proposed structures will suffer damage during the 100-year storm as a result of the Lakeview Subdivision development. G. Modifications of Criteria 1. The proposed Lakeview Subdivision development is not requesting any modifications to criteria at this time. IV. DRAINAGE FACILITY DESIGN A. General Concept 1. The main objectives of the Lakeview Subdivision drainage design are to maintain existing drainage patterns, ensure no adverse impacts to any adjacent properties, and to maintain the drainage concepts as outlined in the First Christian PUD design documents. 2. The existing site does not have any off-site runoff that flows directly through the project site. However, with the development of the site, the stormwater runoff from the existing Church site west of the subject property will continue to flow through the subject property to the proposed regional detention and water quality pond to be located on the south end of the subject property. All detention and water quality calculations within this Drainage Report account for runoff from the entirety of the site as delineated within the First Christian PUD documents. 3. A list of tables and figures used within this report can be found in the Table of Contents at the front of the document. The tables and figures are located within the sections to which the content best applies. 4. The First Christian PUD documents divided the site into two (2) major drainage basins, designated as Basins A and B. The subject property is located within Basin B. Said documents further subdivided Basin B in to three (3) sub-basins, designated as Basins B1, B2, and B3. This project has further divided Basin B3 into three (3) additional basins in order to better calculate hydraulic capacities of streets and better approximate overall times of concentration. The drainage patterns anticipated for each sub-basin within Basin B are further described below. Basin B1 Basin B1 consists of a portion of the existing Church property located south of the existing Church building and west of the street-like private drive from Drake Road that bisects the property. This basin is comprised of roof top area, drive lanes, and a large area of landscaping. The basin drains towards the east and south where it is conveyed to the proposed water quality and detention pond via street gutters through basin B3-1. Lakeview Subdivision Final Drainage Report 9 Basin B2 Basin B2 consists of a portion of the existing Church property south of the existing Church building and west of the street-like private drive from Drake Road that bisects the property. The vast majority of this basin is comprised of existing parking lot and drive lane. The basin drains towards south and east to a point directly west of the proposed detention pond where the runoff will be intercepted and delivered to the pond through inlets and storm sewer. Major storm runoff will overtop the curb and gutter adjacent the pond and will be conveyed into the pond. Basin B3-1 Basin B3-1 consists of 2.85-acres of single family along the west side of the existing Church athletic facilities east of the private drive. Basin B3-1 is one of the basins where the proposed development will occur. In the proposed condition, the basin will consist of residential streets, single family residential lots and landscaped open area. The entirety of the basin will be directed to the south via gutter flows and storm sewer to the proposed detention and water quality pond. Basin B3-2 Basin B3-2 consists of 6.18-acres of single family along the north and east sides of the existing Church athletic facilities east of the private drive, along with a small portion of the existing Church building and parking area to the west. Basin B3-2 is the second basin where the proposed development will occur. In the proposed condition, the basin will consist of residential streets, single family residential lots and landscaped open area. The entirety of the basin will be directed to the south via gutter flows and storm sewer to the proposed detention and water quality pond. Basin B3-3 Basin B3-3 consists of 1.96-acres of open area and detention pond along the south side of the existing Church athletic facilities east of the private drive. Basin B3-3 is the third basin where the proposed development will occur. In the proposed condition, the basin will consist of the back of residential lots and a large detention pond area. The basin will be the collection point for runoff from all other basins and will discharge into the existing detention pond on City property. In addition to the above basins included within the First Christian PUD documents, there are two (2) off-site basins that currently exist on the subject property. These basins are further described below. Basin OS1 Basin OS1 consists of a small area at the north edge of the subject property that drains directly to East Drake Road via overland and gutter flows. The vast majority of this basin is comprised of landscaped area; however a small portion of parking area and drive lane is also included. The proposed development reroutes a portion of the impervious parking area to the east for water quality treatment and extended release. However, the majority of the off-site runoff from this basin will continue to drain to East Drake Road. Basin OS2 Basin OS2 consists of a small area at the south edge of the subject property that drains towards the south into the existing City of Fort Collins detention facility. The vast majority of this basin is comprised of landscaped area. Due to existing physical Lakeview Subdivision Final Drainage Report 10 constraints, the proposed development will continue to allow this basin to drain off- site. A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of this report. B. Specific Details 1. The main drainage problem associated with this project site is the deficiency of the existing detention pond located at the south side of the subject property. Specifically, as determined from a recent topographic survey of the pond, it appears that the existing pond was not built per the original plans and is currently undersized, as the actual spill elevation of the pond is approximately 2.2-feet below the designed elevation. In order to accommodate the required detention and water quality volumes, the proposed top of pond elevation must be raised. Due to the proximity of existing residential properties adjacent to the detention area, special attention has been given to this issue in order to minimize any aesthetic impacts the new pond elevations may have. The development team has attempted to accomplish this by: Providing retaining walls rather than large berms to adjust the top of pond elevations, reduce the aerial extent of the pond and to provide and aesthetic quality to the pond. Maintain existing mature trees on the east edge of the existing pond. Provide additional landscaping around the detention pond to "soften" the appearance of the pond and associated walls. Provide flat areas at the bottom of the pond as passive open space. 2. As previously stated, detention will be provided at the southern portion of the subject property with an outlet connecting to the existing City of Fort Collins detention facility. A SWMM model has been utilized to determine the detention storage volume to be provided within the pond. Water quality is also being provided for the proposed development, as well as for the existing drainage basins as described in Section IV.A.4 of this report. To achieve this objective, water quality is being accomplished through a multi-tiered, comprehensive approach by providing the following BMPs: Water quality Snouts upstream of each discharge location into the proposed pond. Sedimentation pre-forebay settling basing within the inlets. Sediment forebays at the inlets to the pond to allow sediment to settle from the incoming stormwater runoff before being delivered to the main pond facility. Drywells and bioretention media used to promote infiltration. Micro pool utilized within the outlet structure of from the pond for final treatment. 40-hour release water quality outlet to promote further sedimentation. The proposed water quality approach through the treatment BMPs, as noted above, is comprehensive in nature. Further documentation of treatment volumes and removal rates of each BMP will be documented with the Final Drainage Report prepared during the City FDP process. Final design details, construction documentation, and Standard Operating Procedures (SOP) Manual shall be provided to the City of Fort Collins for review prior to Final Development Plan approval. A final copy of the approved Lakeview Subdivision Final Drainage Report 11 SOP manual shall be provided to City and is intended to be maintained on-site by the entity responsible for the facility maintenance. Annual reports must also be prepared and submitted to the City discussing the results of the maintenance program (i.e. inspection dates, inspection frequency, volume loss due to sedimentation, corrective actions taken, etc.). 3. Table 1, below, summarizes the detention storage and water quality information for the main drainage facility. Table 1 – Detention Storage Summary Required Provided B 4.39 4.69 3.7(a) 4967.43 4967.70 4968.70 1.27 b. See Section IV.B.2 for information regarding water quality treatment within the pond. a. Peak Discharge rate as provided by the First Christian PUD drainage documents. 100-year Water Surface Elevation (ft) 100-year Detention Basin ID Storage Volume (cu-ft) 100-year Peak Discharge Pond Spillway Elevation Top of Pond Elevation Freeboard Provided (ft) 4. Proper maintenance of the drainage facilities designed with the Lakeview Subdivision development is a critical component of their ongoing performance and effectiveness. The stormwater detention and water quality pond, as well as the BMP facilities contained therein, may be accessed by maintenance staff via drive-over curb and gutter and the 8’ access ramp/pan provided to the bottom of the pond from the north side. Operations and maintenance of the bioretention areas and sand filters shall follow the recommendations for bioretention (rain garden) facilities, as outlined in the UDFCD manual. Appendix D contains applicable excerpts to serve as guidance for the professional maintenance staff and subcontractors responsible for maintenance of these facilities at the Lakeview Subdivision development. Maintenance of the stormwater water quality Snouts provided shall follow the recommendations provided by the manufacturer. Appendix D will contains applicable excerpts to serve as guidance for the professional maintenance staff and subcontractors responsible for maintenance of these facilities at the Lakeview Subdivision development. 5. The drainage features associated with the Lakeview Subdivision project are all private facilities, located on private property. However, the new detention and water quality facility and associated storm sewers serve publically accessed roads and multiple lots. All storm facilities will be provided in a within drainage easements or tracts dedicated as such. 6. As previously mentioned, the outfall for the entire Lakeview Subdivision project is the existing COFC detention facility located south of the subject property. This facility discharges flows near the southeast corner into an existing 21-inch storm sewer. Stormwater conveyed by this City drainage system ultimately reaches Nelson Reservoir east of the site. There are no additional facilities or upgrades needed off- site in order to accommodate the developed runoff from the Lakeview Subdivision development. Lakeview Subdivision Final Drainage Report 12 V. CONCLUSIONS A. Compliance with Standards 1. The drainage design proposed with the Lakeview Subdivision project complies with the City of Fort Collins’ Stormwater Criteria Manual. 2. The drainage design proposed with the Lakeview Subdivision project complies with the City of Fort Collins’ Master Drainage Plan for the Foothills Drainage Basin. 3. There are no regulatory floodplains associated with the Lakeview Subdivision development. 4. The drainage plan and stormwater management measures proposed with the Lakeview Subdivision development are compliant with all applicable State and Federal regulations governing stormwater discharge. B. Drainage Concept 1. The drainage design proposed with this project will effectively limit any potential damage associated with its stormwater runoff by providing a regional detention pond that will serve the proposed Lakeview Subdivision development and existing Christ Center Community Church facilities. The proposed on-site stormwater facilities will also offer substantial water quality treatment, in addition to peak volume attenuation, through a comprehensive water quality treatment approach that includes multiple stormwater BMPs. 2. The proposed Lakeview Subdivision development will not have any impact on the Master Drainage Plan recommendations for the Foothills Drainage Basin. Lakeview Subdivision Final Drainage Report 13 References 1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities, November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility Services. 2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No. 174, 2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code. 3. Geotechnical Investigation, Regency Multi-Family Residential, 2700 South Lemay Avenue, Fort Collins, Colorado, August 24, 2011, CTL Thompson, Inc.(CTL Thompson Project No. FC05622-115). 4. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007. 5. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation Service, United States Department of Agriculture. 6. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008. APPENDIX A HYDROLOGIC COMPUTATIONS Lakeview Subdivision CHARACTER OF SURFACE1: Runoff Coefficient Percentage Impervious Project: Lakeview Subdivision Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: R. Banning Asphalt ……....……………...……….....…...……………….…………… 0.95 100% Date: Concrete …….......……………….….……….………………..….……… 0.95 90% Gravel ……….…………………….….…………………………..………… 0.50 40% Roofs …….…….………………..……………….………………………… 0.95 90% General Single Family …………………………...………………..……… 0.60 50% Total Increase in Imperviousness Area Lawns and Landscaping 4.48 Acres Sandy Soil Flat <2% ………………………………………………………………… 0.10 0% Average 2% to 7% ……………………………………………………… 0.15 0% Steep >7% ……………………………………………………………… 0.20 0% Clayey Soil Flat <2% ………………………………………………………………… 0.20 0% Average 2% to 7% ……………………………………………………… 0.25 0% Steep >7% ……………………………………………………………… 0.35 0% 2-year Cf = 1.00 10-year Cf = 1.00 100-year C f = 1.25 Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11 Basin ID Basin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Gravel (ac) Area of Roofs (ac) Area of Single Family (ac) Soil Type and Average Slope Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. Lakeview Subdivision Overland Flow, Time of Concentration: Lakeview Subdivision Gutter/Swale Flow, Time of Concentration: Tt = L / 60V Tc = Ti + Tt (Equation RO-2) Velocity (Gutter Flow), V = 20·S½ Velocity (Swale Flow), V = 15·S½ NOTE: C-value for overland flows over grassy surfaces; C = 0.25 Is Length >500' ? C*Cf (2-yr Cf=1.00) C*Cf (10-yr Cf=1.00) C*Cf (100-yr Cf=1.25) Length, L (ft) Slope, S (%) Ti 2-yr (min) Ti 10-yr (min) Ti 100-yr (min) Length, L (ft) Slope, S (%) Velocity, V (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) B1 B1 No 0.53 0.53 0.66 210 1.90% 12.5 12.5 9.6 566 1.10% 2.10 4.5 17.0 17.0 14.1 B2 B2 No 0.80 0.80 1.00 205 1.20% 7.6 7.6 2.5 540 1.30% 2.28 3.9 11.5 11.5 6.5 B3-1 B3-1 No 0.63 0.63 0.79 165 3.60% 7.3 7.3 4.8 640 1.40% 2.37 4.5 11.8 11.8 9.3 B3-1 B3-2 No 0.58 0.58 0.73 65 3.10% 5.4 5.4 3.9 1150 1.00% 2.00 9.6 14.9 14.9 13.4 B3-3 B3-3 No 0.28 0.28 0.34 50 2.00% 8.7 8.7 7.9 400 0.50% 1.41 4.7 13.4 13.4 12.7 Lakeview Subdivision Rational Method Equation: Project: Lakeview Subdivision Calculations By: Date: Rainfall Intensity: B1 B1 2.84 17.0 17.0 14.1 0.53 0.53 0.66 1.75 2.99 6.71 2.62 4.48 12.57 B2 B2 4.70 11.5 11.5 6.5 0.80 0.80 1.00 2.09 3.57 9.31 7.87 13.42 43.80 B3-1 B3-1 2.85 11.8 11.8 9.3 0.63 0.63 0.79 2.09 3.57 8.03 3.77 6.44 18.12 B3-1 B3-2 6.18 14.9 14.9 13.4 0.58 0.58 0.73 1.90 3.24 6.92 6.81 11.64 31.08 B3-3 B3-3 1.96 13.4 13.4 12.7 0.28 0.28 0.34 1.98 3.39 7.04 1.07 1.83 4.75 B3-1 B1&B3-1 5.69 18.3 18.3 15.2 0.58 0.58 0.73 1.70 2.90 6.52 5.62 9.58 26.93 B3-1 B1,B3-1 & B3-2 11.87 18.3 18.3 15.2 0.58 0.58 0.73 1.70 2.90 6.52 11.72 20.00 56.21 OS1 OS1 0.52 9.3 9.3 9.0 0.22 0.22 0.28 2.30 3.93 8.21 0.27 0.46 1.20 OS2 OS2 0.19 7.1 7.1 7.0 0.15 0.15 0.19 2.52 4.31 8.80 0.07 0.13 0.32 B Overall B Overall 18.54 18.7 18.7 15.4 0.60 0.60 0.76 1.68 2.86 6.52 18.76 32.03 91.28 Notes RUNOFF COMPUTATIONS R. Banning November 19, 2013 Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8 Design Point Basin(s) Area, A (acres) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) Flow, Q2 (cfs) Flow, Q10 (cfs) Flow, Q100 (cfs) C2 C 10 C100 Intensity, i2 (in/hr) Intensity, i10 (in/hr) Intensity, i100 (in/hr) Q  C f  C i  A 11/19/2013 12:36 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Runoff Hydrologic Soil Group—Larimer County Area, Colorado (Lakeview Hydrologic Group) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/29/2013 Page 1 of 4 4488730 4488780 4488830 4488880 4488930 4488980 4489030 4489080 4489130 4488730 4488780 4488830 4488880 4488930 4488980 4489030 4489080 4489130 495240 495290 495340 495390 495440 495490 495540 495240 495290 495340 495390 495440 495490 495540 40° 33' 10'' N 105° 3' 22'' W 40° 33' 10'' N 105° 3' 9'' W 40° 32' 57'' N 105° 3' 22'' W 40° 32' 57'' N 105° 3' 9'' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 50 100 200 300 Feet 0 30 60 120 180 Meters Map Scale: 1:2,050 if printed on A portrait (8.5" x 11") sheet. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Larimer County Area, Colorado Hydrologic Soil Group Hydrologic Soil Group— Summary by Map Unit — Larimer County Area, Colorado (CO644) Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 74 Nunn clay loam, 1 to 3 percent slopes C 7.1 42.1% 75 Nunn clay loam, 3 to 5 percent slopes C 0.0 0.0% 76 Nunn clay loam, wet, 1 to 3 percent slopes C 1.5 9.0% 100 Stoneham loam, 0 to 1 percent slopes B 3.3 19.9% 102 Stoneham loam, 3 to 5 percent slopes B 4.8 28.9% 136 Water 0.0 0.1% Totals for Area of Interest 16.8 100.0% Hydrologic Soil Group—Larimer County Area, Colorado Lakeview Hydrologic Group Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/29/2013 Page 3 of 4 Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Larimer County Area, Colorado Lakeview Hydrologic Group Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/29/2013 Page 4 of 4 APPENDIX B HYDRAULIC COMPUTATIONS B.1 – Storm Sewers B.2 – Street Flow B.3 – Inlets B.4 – Detention Facilities APPENDIX B.1 STORM SEWERS Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Nov 19 2013 ST-1 Church Parking Lot Circular Diameter (ft) = 2.00 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.015 Calculations Compute by: Known Q Known Q (cfs) = 7.87 Highlighted Depth (ft) = 1.08 Q (cfs) = 7.870 Area (sqft) = 1.74 Velocity (ft/s) = 4.53 Wetted Perim (ft) = 3.31 Crit Depth, Yc (ft) = 1.00 Top Width (ft) = 1.99 EGL (ft) = 1.40 0 1 2 3 4 Elev (ft) Section Depth (ft) 99.50 -0.50 100.00 0.00 100.50 0.50 101.00 1.00 101.50 1.50 102.00 2.00 102.50 2.50 103.00 3.00 Reach (ft) Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Nov 19 2013 Pond Outfall Pipe Design Flow Circular Diameter (ft) = 1.50 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.015 Calculations Compute by: Known Q Known Q (cfs) = 3.70 Highlighted Depth (ft) = 0.82 Q (cfs) = 3.700 Area (sqft) = 0.99 Velocity (ft/s) = 3.74 Wetted Perim (ft) = 2.50 Crit Depth, Yc (ft) = 0.74 Top Width (ft) = 1.49 EGL (ft) = 1.04 0 1 2 3 Elev (ft) Section 99.50 100.00 100.50 101.00 101.50 102.00 Reach (ft) Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Nov 19 2013 Pond Outfall Pipe Emergency Overflow Capacity Circular Diameter (ft) = 1.50 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.015 Calculations Compute by: Known Depth Known Depth (ft) = 1.50 Highlighted Depth (ft) = 1.50 Q (cfs) = 6.435 Area (sqft) = 1.77 Velocity (ft/s) = 3.64 Wetted Perim (ft) = 4.71 Crit Depth, Yc (ft) = 0.98 Top Width (ft) = 0.00 EGL (ft) = 1.71 0 1 2 3 Elev (ft) Section 99.50 100.00 100.50 101.00 101.50 102.00 Reach (ft) APPENDIX B.2 STREET FLOW Project: Inlet ID: Gutter Geometry (Enter data in the blue cells) Maximum Allowable Width for Spread Behind Curb TBACK = 11.0 ft Side Slope Behind Curb (leave blank for no conveyance credit behind curb) SBACK = 0.020 ft/ft Manning's Roughness Behind Curb nBACK = 0.015 Height of Curb at Gutter Flow Line HCURB = 4.38 inches Distance from Curb Face to Street Crown TCROWN = 15.0 ft Gutter Width W = 1.17 ft Street Transverse Slope SX = 0.020 ft/ft Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft) SW = 0.098 ft/ft Street Longitudinal Slope - Enter 0 for sump condition SO = 0.025 ft/ft Manning's Roughness for Street Section nSTREET = 0.015 Minor Storm Major Storm Max. Allowable Spread for Minor & Major Storm TMAX = 15.0 15.0 ft Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX = 4.4 12.0 inches Allow Flow Depth at Street Crown (leave blank for no) check = yes MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow = 10.0 146.7 cfs Major storm max. allowable capacity GOOD - greater than flow given on sheet 'Q-Peak' ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm) Lakeview Subdivision Maximum Grade 2.5% Street Capacity (Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread) Minor storm max. allowable capacity GOOD - greater than flow given on sheet 'Q-Peak' Street Cap Max Grade.xlsm, Q-Allow 8/20/2013, 8:55 AM Project: Inlet ID: Gutter Geometry (Enter data in the blue cells) Maximum Allowable Width for Spread Behind Curb TBACK = 11.0 ft Side Slope Behind Curb (leave blank for no conveyance credit behind curb) SBACK = 0.020 ft/ft Manning's Roughness Behind Curb nBACK = 0.015 Height of Curb at Gutter Flow Line HCURB = 4.38 inches Distance from Curb Face to Street Crown TCROWN = 15.0 ft Gutter Width W = 1.17 ft Street Transverse Slope SX = 0.020 ft/ft Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft) SW = 0.098 ft/ft Street Longitudinal Slope - Enter 0 for sump condition SO = 0.005 ft/ft Manning's Roughness for Street Section nSTREET = 0.015 Minor Storm Major Storm Max. Allowable Spread for Minor & Major Storm TMAX = 15.0 15.0 ft Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX = 4.4 12.0 inches Allow Flow Depth at Street Crown (leave blank for no) check = yes MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow = 4.4 94.5 cfs Major storm max. allowable capacity GOOD - greater than flow given on sheet 'Q-Peak' ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm) Lakeview Subdivision Min Grade 0.5% Street Capacity (Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread) Minor storm max. allowable capacity GOOD - greater than flow given on sheet 'Q-Peak' Street Cap Min Grade.xlsm, Q-Allow 8/20/2013, 8:55 AM Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Monday, Aug 12 2013 Basin B Street Discharge Triangular Side Slopes (z:1) = 12.00, 12.00 Total Depth (ft) = 1.50 Invert Elev (ft) = 67.62 Slope (%) = 0.50 N-Value = 0.015 Calculations Compute by: Known Q Known Q (cfs) = 11.30 Highlighted Depth (ft) = 0.57 Q (cfs) = 11.30 Area (sqft) = 3.90 Velocity (ft/s) = 2.90 Wetted Perim (ft) = 13.73 Crit Depth, Yc (ft) = 0.57 Top Width (ft) = 13.68 EGL (ft) = 0.70 0 5 10 15 20 25 30 35 40 45 50 Elev (ft) Section Depth (ft) 67.00 -0.62 67.50 -0.12 68.00 0.38 68.50 0.88 69.00 1.38 69.50 1.88 70.00 2.38 Reach (ft) APPENDIX B.3 INLETS Project = Inlet ID = Design Information (Input) MINOR MAJOR Type of Inlet Inlet Type = Local Depression (additional to continuous gutter depression 'a' from 'Q-Allow') alocal = 3.00 3.00 inches Number of Unit Inlets (Grate or Curb Opening) No = 1 1 Water Depth at Flowline (outside of local depression) Flow Depth = 6.0 7.3 inches Grate Information MINOR MAJOR Length of a Unit Grate Lo (G) = N/A N/A feet Width of a Unit Grate Wo = N/A N/A feet Area Opening Ratio for a Grate (typical values 0.15-0.90) Aratio = N/A N/A Clogging Factor for a Single Grate (typical value 0.50 - 0.70) Cf (G) = N/A N/A Grate Weir Coefficient (typical value 2.15 - 3.60) Cw (G) = N/A N/A Grate Orifice Coefficient (typical value 0.60 - 0.80) Co (G) = N/A N/A Curb Opening Information MINOR MAJOR Length of a Unit Curb Opening Lo (C) = 10.00 10.00 feet Height of Vertical Curb Opening in Inches Hvert = 6.00 6.00 inches Height of Curb Orifice Throat in Inches Hthroat = 6.00 6.00 inches Angle of Throat (see USDCM Figure ST-5) Theta = 63.40 63.40 degrees Side Width for Depression Pan (typically the gutter width of 2 feet) Wp = 2.00 2.00 feet Clogging Factor for a Single Curb Opening (typical value 0.10) Cf (C) = 0.10 0.10 Curb Opening Weir Coefficient (typical value 2.3-3.6) Cw (C) = 3.60 3.60 Curb Opening Orifice Coefficient (typical value 0.60 - 0.70) Co (C) = 0.67 0.67 MINOR MAJOR Total Inlet Interception Capacity (assumes clogged condition) Qa = 8.3 13.4 cfs WARNING: Inlet Capacity less than Q Peak for MAJOR Storm Q PEAK REQUIRED = 7.9 43.8 cfs INLET IN A SUMP OR SAG LOCATION Lakeview Subdivision Church Parking Lot Inlet B2 Capacity CDOT Type R Curb Opening H-Vert H-Curb W Lo (C) Lo (G) Wo WP Inlet Capacity Parking Lot.xlsm, Inlet In Sump 11/19/2013, 9:24 AM APPENDIX B.4 DETENTION FACILITIES Lakeview Subdivision SWMM Exhibit Project: Lakeview Date: 11/19/2013 11/19/2013 12:38 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\SWMM Exhibit Lakeview Subdivision St Stage - Storage St Calculation C l l ti 665 002 gg Project Number: 665-002 F t C lli C l d Project Number: Pjt Project Location: L ti Fort Collins, Colorado Calculations By: R. Banning Date: 11/19/2013 Pond No : N/A Calculations By: Pond No.: N/A Required Volume Water Surface Elevation (WSE) Design Point B3 3 q B3-3 100 Design Point Di Design Storm S 100-yr Require Volume= 439 4.39 acft 4967 4967.43 ft ft. Require Volume= Design Storm WQCV Ri Required d V Volume= l 16772 ft3 4962 4962.63 ft ft. Contour Contour Elevation (Y- Contour Area Depth SWMM Stage Incremental Volume Total Volume Total Volume values) Area p g values) ft3 ft ft ft. ft ft3 ft ft3 ft acre-acre feet 4 4,960 960.70 0 000 0.00 0 0 0 0 4 4,961 961.00 113 030 0.30 -1.1 63 11 11 000 0.00 4 4,962 962.00 11385 100 1.00 -0.063 63 4207 4218 010 0.10 4,963.00 29970 1.00 0.37 19922 24140 0.55 4 4,964 964.00 32671 100 1.00 137 1.37 31279 55420 127 1.27 4 4,965 965.00 36597 100 1.00 237 2.37 34581 90000 207 2.07 4,, 966.00 40815 1.00 3.37 38648 128649 2.95 4 4,967 967.00 42827 100 1.00 437 4.37 41775 170424 391 3.91 4 4,967 967.70 54225 070 0.70 507 5.07 33856 204280 469 4.69 4 4,969 969.00 4,968.00 4,96 967.00 n 4 966 00 ion 4,966.00 El ev vat 4 965 00 ur 4,965.00 Co ont tou 4,, 964.00 4 4,963 963.00 4 4,962 962.00 -50000 0 50000 100000 150000 200000 250000 Cummulative Volume Volume, cu cu. ft ft. Lakeview Subdivision ORIFICE RATING CURVE Pond Outlet 100-yr Orifice Project: Lakeview Subdivision Date: 11/19/2013 By: R. Banning 100-yr WSEL= 4967.43 Orifice Plate Outflow Q 3.7 cfs Orifice Coefficient Cd 0.65 Gravity Constant g 32.2 ft/s^2 100-year head H 6.73 ft Orifice Area Ao 0.27 ft^2 Orifice Area Ao 39.37 in^2 Radius r 3.5 in Diameter d 7.1 in Orifice Curve Stage (ft) H (ft) Q (cfs) SWMM Stage Note 4960.70 0 0.00 Pond Invert 4961.70 1 1.43 4962.63 1.93 1.98 0 WQ WSEL 4963.63 2.93 2.44 1.00 4964.63 3.93 2.83 2.00 4965.63 4.93 3.17 3.00 4966.63 5.93 3.47 4.00 4967.43 6.73 3.70 4.80 100-yr WSEL 4967.63 6.93 3.75 5.00 4967 70 3 0 Oi 11/19/2013 12:38 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Orifice Size 4967.70 7 3.77 5.07 Overtopping 11/19/2013 12:38 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Orifice Size Weir Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Wednesday, Nov 20 2013 Lakeview Pond Overflow Weir Trapezoidal Weir Crest = Sharp Bottom Length (ft) = 100.00 Total Depth (ft) = 1.00 Side Slope (z:1) = 4.00 Calculations Weir Coeff. Cw = 3.10 Compute by: Known Q Known Q (cfs) = 91.30 Highlighted Depth (ft) = 0.44 Q (cfs) = 91.30 Area (sqft) = 44.77 Velocity (ft/s) = 2.04 Top Width (ft) = 103.52 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Depth (ft) Lakeview Pond Overflow Weir Depth (ft) -0.50 -0.50 0.00 0.00 0.50 0.50 1.00 1.00 1.50 1.50 2.00 2.00 Weir W.S. Length (ft) APPENDIX C WATER QUALITY DESIGN COMPUTATIONS Lakeview Subdivision WQ Capture & Forebay Volumes Project: Lakeview Subdivision Date: 11/19/2013 By: R. Banning B3-2 I= 50% WQCV From Figure 3.2 USDCM 40-hour 0.24 watershed inches Required Storage 0.124 Acre-ft 5385 ft^3 TOTAL AREA I= 53% WQCV From Figure 3.2 USDCM 40-hour 0.24 watershed inches Required Storage 0.385 Acre-ft 16772 ft^3 B2 I= 81% Area 4.704 acres WQCV From Figure 3.2 USDCM 40-hour 0.33 watershed inches Required Storage 0.129 Acre-ft 5635 ft^3 Forbay Volume 113 ft^3 Depth 12 in North Forebay I= 50% Area 11.87 acres WQCV From Figure 3.2 USDCM 40-hour 0.21 watershed inches Required Storage 0.208 Acre-ft 9048 ft^3 Forbay Volume 181 ft^3 Depth 18 in 11/19/2013 12:37 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\WQ Capture Lakeview Subdivision FOREBAY NOTCH RATING CURVE Forebay A WQ V-notch Project: Lakeview Subdivision Date: 11/19/2013 By: R. Banning Orifice Plate Outflow Q0.88 cfs Orifice Coefficient Cd 0.6 Gravity Constant g 32.2 ft/s^2 Notch Top Width W top 0.37 ft Notch Top Width W top 4.4 in Forebay Wall Height h1 ft Notch Area Ao 0.18 ft^2 Notch Area Ao 26.32 in^2 Angle theta 0.18 Orifice Curve Stage (ft) a w A (ft^2) Q (cfs) 0 0.00 0.00 0.00 0.00 0.1 0.02 0.04 0.00 0.00 0.2 0.04 0.07 0.01 0.02 0.3 0.05 0.11 0.02 0.04 04 007 015 003 009 a h 0.4 0.07 0.15 0.03 0.09 0.5 0.09 0.18 0.05 0.16 0.6 0.11 0.22 0.07 0.25 0.7 0.13 0.26 0.09 0.36 0.8 0.15 0.29 0.12 0.50 0.9 0.16 0.33 0.15 0.68 1 0.18 0.37 0.18 0.88 11/19/2013 12:38 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Forebay A Notch Lakeview Subdivision FOREBAY NOTCH RATING CURVE Forebay B WQ V-notch Project: Lakeview Subdivision Date: 11/19/2013 By: R. Banning Orifice Plate Outflow Q1.12 cfs Orifice Coefficient Cd 0.6 Gravity Constant g 32.2 ft/s^2 Notch Top Width W top 0.25 ft Notch Top Width W top 3.0 in Forebay Wall Height h1.5 ft Notch Area Ao 0.19 ft^2 Notch Area Ao 27.35 in^2 Angle theta 0.08 Orifice Curve Stage (ft) a w A (ft^2) Q (cfs) 0 0.00 0.00 0.00 0.00 0.1 0.01 0.02 0.00 0.00 0.2 0.02 0.03 0.00 0.01 0.3 0.03 0.05 0.01 0.02 04 003 007 001 004 a h 0.4 0.03 0.07 0.01 0.04 0.5 0.04 0.08 0.02 0.07 0.6 0.05 0.10 0.03 0.11 0.7 0.06 0.12 0.04 0.17 0.8 0.07 0.14 0.05 0.23 0.9 0.08 0.15 0.07 0.31 1 0.08 0.17 0.08 0.41 1.1 0.09 0.19 0.10 0.52 1.2 0.10 0.20 0.12 0.64 1.3 0.11 0.22 0.14 0.78 1.4 0.12 0.24 0.17 0.94 1.5 0.13 0.25 0.19 1.12 11/19/2013 12:38 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Forebay B Notch APPENDIX D OPERATIONS AND MAINTENANCE GUIDELINES FOR PERMANENT BMPS Lakeview Subdivision Final Operation and Maintenance Guide PERMANENT BMP OPERATION AND MAINTENANCE GUIDE The Lakeview Subdivision private drainage facilities contain permanent BMPs that must be maintained by the Homeowners. The following is the recommended maintenance measures and schedule for each permanent BMP. Pre-forebay/Sedimentation Sump Description The pre-forebay is a system of measures within the inlet located in the drive aisle between the church parking facility and the Lakeview Subdivision detention pond. The system consists of sedimentation sump and snout apparatus. The sedimentation sump is extra volume (2-3’ deep) at the bottom of the inlet and below invert of the outlet pipe. The Snout apparatus is a hood shaped devise that covers the outlet pipe from the inlets. Function The inlet will contain a perpetual pool of water within the sedimentation sump between the invert (bottom) and the bottom of the snout apparatus. The pool is intended to allow for sedimentation by pausing the motion of water prior to discharge from the inlet. The increased time runoff resides within the inlet will allow for a minimal amount of sedimentation and allow for separation of hydrocarbons from runoff. The snout apparatus is intended to separate hydrocarbons (ie. oil) from impervious area runoff by skimming the top of the pool. Hydrocarbons will separate from runoff and buildup within the top layer of the permanent pool. Runoff from below the hydrocarbons and the bottom of the snout will outfall into the pond. Maintenance Hydrocarbons and sediment will need to be removed regularly from the inlet. Sediment should be removed prior to the depth of the water reducing below 2’ from the top of the sediment buildup to the snout bottom. The layer of hydrocarbons should be removed from the inlet prior to accumulation beyond half of the height of the snout. A vacuum truck should be used to remove all sediment, hydrocarbons and residual water from the inlet. Remaining sediment may be removed manually and disposed of in a legal manner. The sump should then be filled with clean water. The Snout apparatus should be replaced as age deterioration occurs and prior to failure. The seal should be checked regularly to ensure hydrocarbons are not bypassing the device. Schedule Maintenance should occur as triggered by the conditions indicated above and at least bi-annually. Lakeview Subdivision Final Operation and Maintenance Guide Sedimentation Forebay Description The sedimentation forebays are concrete lined pool made with concrete or earthen berm walls 1-2’ tall, located strategically throughout the drainage basin and at pond inlet. The forebays contain small outlet pipes or notches and measures including concrete aprons or riprap to minimize erosion when overtopping occurs. Energy dissipation including small walls or buried boulders may be included in the forebay design just below the inlet to the forebay. Function The forebay will allow runoff to pool in a convenient place prior to entering the pond. There is an extended outfall time designed for each basin. The increased residence time of runoff within the forebay is intended to allow sedimentation from the runoff prior to entering the pond. The concrete bottom is intended to allow for easy removal of sediment by shoveling or mechanical methods. The forebay will normally be slightly wet unless evaporation of runoff within the forebay occurs between runoff events. Maintenance Sediment should be regularly removed from the forebay and legally disposed of. Removal is normally achieved by shoveling in some fashion. Maximum sediment accumulation should be 4” at the outlet from the forebay. Sprinklers should be positioned to avoid spraying within the forebay to minimize damp conditions and conditions favorable to mosquito breeding. Schedule Maintenance should occur as triggered by the conditions indicated above and at least bi-annually. Lakeview Subdivision Final Operation and Maintenance Guide Drywell – See attached FAQ sheet for additional information Description The drywell is a method of promoting infiltration. The facility is a vertical well, either empty or filled with gravel material to achieve filtering. Material surrounding the well consists of washed rock, providing volume for runoff within the voids prior to recharging into groundwater. Drywells and surrounding materials are usually wrapped with geotexile fabrics to prevent sediment deposition within voids. Where implemented, gravel and geotextile fabrics should be used perpetually to reduce the maintenance requirements. Function Runoff is designed to accumulate around and enter into the inlet to the drywells. Runoff will percolate into the voids of the surrounding materials and ultimately recharge into groundwater. Maintenance Water quality and sedimentation facilities upstream of any drywell should be maintained properly to extend the useful life of the drywell. Geotextile/Filter fabrics should be inspected regularly and replaced when sediment load prevents runoff from free passing through the fabric. Gravels within the drywell should be removed and replaced as sediment accumulates within the media. Surrounding materials should be replaced along with an additional 4” of native material adjacent the surrounding material if fabrics and gravels are replaced but function is not restored. Schedule Maintenance should occur as triggered by the conditions indicated above and at least bi-annually. Lakeview Subdivision Final Operation and Maintenance Guide Bio-retention Materials Description Bio-retention materials allow vegetative growth and promote infiltration of runoff where used. The material should be underlined by a porous media such as sand or pea gravels to increase the infiltration potential. Geotextile fabric should be implemented between the bio-retention materials and the porous media to minimize sediment migration into the porous material and to define the limits of the bio-retention material. Bio-retention materials should be planted with wetland plants and those with sparse root systems. Bio-retention materials should only be used were erosive potential is extremely low. Function Bio-retention materials are places in areas where runoff is very slow or pooling of water will occur. Wetland material growth will occur and promote degradation of pollutants and sedimentation through natural processes and runoff impedance. Runoff will also infiltrate into the material increasing the potential for groundwater recharge. Maintenance Growth of wetland materials should be allowed perpetually within bio-retention median and only be cut or mowed when additional maintenance such as trash removal is required. Bi-annual Aeration of bio-retention media is recommended to increase the infiltration potential. The material may need to be replaced as sediment loading occurs to restore infiltration potential. When required the media should be removed along with the underlying geotextile fabric. Underlying porous material should be tested to insure infiltration capacity has not been compromised. The geotexile fabric and bio- retention material should then be replaced and replanted. Schedule Maintenance should occur as triggered by the conditions indicated above and at least bi-annually. Lakeview Subdivision Final Operation and Maintenance Guide Micro-pool and Initial Surcharge Volume Description The micro-pool is located adjacent the outlet from the pond. The pool is intended to promote microbial growth that consumes organic materials in runoff. The pool contains a concrete bottom and ramp to facilitate maintenance. The pool is surrounded with boulders or berms to increase the depth of the pool above the outlet invert, creating the initial surcharge volume. Function Micro-pools promote microbial growth and are intended to be at sufficient depth to increase organic consumption and minimize insect breeding habitat. The stagnant pool is necessary to achieve the benefit of pollutant reduction. The initial surcharge volume provides a place for minor storms to accumulate around the outlet while minimizing the saturated soils at the bottom of the pond. This serves to increase the lower level outfall through the water quality plate and minimize insect breeding areas. Maintenance The micro-pool should be allowed to accumulate water with minimal disturbance. The pool may become anaerobic promoting consmption of organics. The sediment and water from the pool should be removed when the accumulation has decreased the pool depth to 2’ or less to minimize insect habitat. Removal should be by legal method only and may require a vacuum truck. Remaining sediment should be manually removed and the pool should be refilled with clean water. The initial surcharge volume should be restored to the plan elevations during sediment removal. Schedule Maintenance should occur as triggered by the conditions indicated above and at least bi-annually. Lakeview Subdivision Final Operation and Maintenance Guide Water Quality Outlet Structure Description The water quality outlet structure is a multi-cell concrete structure that contains orifice plates for regulating release from the pond. Trash racks are installed over the plates to minimize clogging. The outfall from the structure is to a pipe or swale outside of the pond. Function The plates are installed to slow the release of water creating a 40-hour water quality release pool and minimizing the 100-year release to allowable per downstream requirements. The pond will accumulate volume as designed due to the restriction of outflow. Maintenance The orifice plates must be installed and properly maintained within the water quality outlet structure. Failure to install the plates will overwhelm downstream storm conveyance. Failure to properly maintain the plates may create unintended perpetual pools within the pond or an overtopping condition during major storms. Upstream sedimentation facilities should be maintained to increase the longevity and reduce the maintenance of the overall pond. Sediment should be removed from the pond when these structure no longer function. Due to these structures sediment should never accumulate at the water quality plate within the structure. Major pond maintenance may be required if this condition takes place. Trash racks should be cleaned of debris regularly and immediately if debris accumulates on the racks. The orifice plates should be inspected for degradation and replaced if no longer functional as designed. Sediment and debris should be cleaned at least bi-annually from the bottom of the structure and the outlet pipe behind the orifice plates. Ensure that the integrity of the racks brackets and the overall structures are not compromised and replace as needed. Schedule Maintenance should occur as triggered by the conditions indicated above and at least bi-annually. Overview Inﬁltration trenches and dry wells are standard stormwater management structures that can play an important role in Low Impact Development site design. Dispersed around the site, these inﬁltration structures can recharge groundwater and help to maintain or restore the site’s natural hydrology. This approach contrasts with conventional stormwater management strategies, which employ inﬁltration as a secondary strategy that occurs in large basins at the end of a pipe. Dry wells and inﬁltration trenches store water in the void space between crushed stone or gravel; the water slowly percolates downward into the subsoil. An overﬂow outlet is needed for runoff from large storms that cannot be fully inﬁltrated by the trench or dry well. Bioretention, another important inﬁltration technique, is discussed in another fact sheet. Inﬁltration trenches do not have the aesthetic or water quality beneﬁts of bioretention areas, but they may be useful techniques where bioretention cells are not feasible. Applications and Design Principles Inﬁltration structures are ideal for inﬁltrating runoff from small drainage areas (<5 acres), but they need to be applied very carefully. Particular concerns include potential groundwater contamination, soil inﬁltration capacity, clogging, and maintenance. Pretreatment is always necessary, except for uncontaminated roof runoff. Trenches and dry wells are often used for stormwater retroﬁts, since they do not require large amounts of land; directing roof runoff to drywells is a particularly cost-effective and beneﬁcial practice. Whether for retroﬁts or new construction, multiple inﬁltration structures will be needed to treat large sites; they are often used in the upland areas of large sites to reduce the overall amount of runoff that must be treated downstream. Trenches and dry wells are tough to site in dense urban settings, due to the required separation from foundations, and because urban soils often have poor inﬁltration capacity due to many years of compaction. Inﬁltration trenches and dry wells should not receive runoff from stormwater hotspots Low Impact Development strategies use careful site design and decentralized stormwater management to reduce the environmental footprint of new growth. This approach improves water quality, minimizes the need for expensive pipe-and-pond stormwater systems, and creates more attractive developments. F A C T S H E E T # 5 INFILTRATION TRENCHES AND DRY WELLS Management Objectives Remove suspended solids, heavy metals, trash, oil and grease. Reduce peak discharge rate and total runoff volume. Provide modest inﬁltration and recharge. Provide snow storage areas. Improve site landscaping. M A S S A C H U S E T T S L OW I M PACT D E V E L O P M E N T T O O L K I T (such as gas stations) unless the stormwater has already been fully treated by another stormwater treatment practice to avoid potential groundwater contamination. Inﬁltration structures must be constructed with adequate vertical separation from the groundwater table, generally 2’ or more between the bottom of the trench or pit and the seasonally high groundwater table. Soils must be sufﬁciently permeable (at least 0.3”/hour) to ensure that trenches can inﬁltrate quickly. Inﬁltration trenches and dry wells operate on similar principles, though trenches are linear troughs and dry wells are round or square in plan view. In both cases, the excavated hole or trench, 3’-12’ deep, is lined with ﬁlter fabric and backﬁlled with washed, crushed stone 1.5”-3” in diameter. The bottom of inﬁltration trenches is often ﬁlled with a 6”-12” ﬁlter layer of washed, compacted sand. A 4”-6” perforated PVC observation well will permit monitoring of the structure and observation of drainage time. Trenches and dry wells should be designed to store the design volume and inﬁltrate it into the ground through the bottom of the trench or well within 72 hours. Because of their limited size, inﬁltration structures are best used to inﬁltrate the ﬁrst inch/half inch of runoff from frequent small storms; they are not effective for inﬁltrating the runoff from large storms. Overﬂow from trenches and dry wells should be directed to a swale or other conveyance, sized to prevent erosion. Because dry wells and inﬁltration trenches can be prone to clogging, pretreatment of stormwater runoff is a necessity. Where dry wells accept roof runoff through a system of gutters and downspouts, screens at the top of downspouts should sufﬁce. For runoff from paved surfaces, designers should use grass swales, ﬁlter strips, settling basins, sediment forebays, or a combination of two or more strategies to pretreat stormwater before it is discharged to an inﬁltration trench or dry well. In groundwater protection areas (Zone II and Interim Wellhead Protection Areas) inﬁltration may only be used for uncontaminated rooftop runoff. Above, top: A perforated pipe delivers rooftop runoff to the full length of this inﬁltration trench, under construction. After comple- tion the area will be covered with sod and the trench will be invisible. Photo: Cahill Associates, Inc. 2004 Above: A roadside inﬁltration trench that receives runoff via periodic curb cuts; this trench may be prone to clogging because there is no pretreatment. Photo: Lower Columbia River Estuary Partnership Right: A schematic section of an in- ﬁltration basin. Image: American Groundwater Trust, Plainﬁeld CT Stormwater Manual Beneﬁts and Effectiveness Dry wells and inﬁltration trenches reduce stormwater runoff volume, including most of the runoff from small frequent storms. Consequently, downstream pipes and basins are smaller, and the local hydrology beneﬁts from increased base ﬂow. Dry wells and inﬁltration trenches also reduce peak discharge rates by retaining the ﬁrst ﬂush of stormwater runoff and creating longer ﬂow paths for runoff. Inﬁltration structures are moderately expensive to construct and can help to reduce the size of downstream stormwater management structures. These techniques have an unobtrusive presence; they do not enhance the landscape (like bioretention areas do), but they have a lower proﬁle than large inﬁltration basins. Limitations Inﬁltration trenches and dry wells cannot receive untreated stormwater runoff, except rooftop runoff. Pretreatment is necessary to prevent premature failure that results from clogging with ﬁne sediment, and to prevent potential groundwater contamination due to nutrients, salts, and hydrocarbons. Inﬁltration structures cannot be used to treat runoff from portions of the site that are not stabilized. Rehabilitation of failed inﬁltration trenches and dry wells requires complete reconstruction. Inﬁltration structures are difﬁcult to apply in slowly permeable soils or in ﬁll areas. Where possible, the design should maintain a minimum separation from paved areas (generally 10’, depending on site conditions) to prevent frost heave. Unlike bioretention areas, inﬁltration trenches and dry wells do not help meet site landscaping requirements. Above, and Cover: The parking lot runoff directed to this inﬁltration basin is pretreated by a vegetated ﬁlter strip. Note concrete level spreader (at right) to facilitate sheetﬂow across ﬁlter strip. Photo:California Stormwater Quality Association Design Details Determine inﬁltration rate of underlying soil through ﬁeld investigations; use a minimum of one boring at each dry well, two borings at each inﬁltration trench, with at least one additional boring every 50 feet for trenches over 100 feet. Base trench/drywell sizing on the slowest rate obtained from soil inﬁltration tests. Determine the inﬁltrative capacity of the soil through an inﬁltration test using a double-ring inﬁltrometer. Do not use a standard septic system percolation test to determine soil permeability. Do not use trenches or dry wells where soils are >30% clay or >40% silt clay. Use of vertical piping for distribution or inﬁltration enhancement may cause the trench or drywell to be classiﬁed as an injection well which needs to be registered with the state. Trim tree roots ﬂush with the trench sides in order to prevent puncturing or tearing the ﬁlter fabric. Since tree roots may regrow, it may be necessary to remove all trees within 10 feet of the inﬁltration structure and replace them with shallow-rooted shrubs and grasses. If used, distribution pipes should have perforations of 0.5” and should be capped at least 1 foot short of the wall of the trench or well. For inﬁltration trenches receiving runoff via surface ﬂow, a horizontal layer of ﬁlter fabric just below the surface of the trench, covered with 2”-6” of gravel or crushed stone, will help to retain sediment near the surface; this will prevent clogging and allow for rehabilitation of the trench without complete reconstruction. Required set backs for surface water supply (Zone 1 and Zone A): 400 feet setback from a source and 100 feet from tributaries. Required setback from private wells: 100 feet Required setback from septic systems: 100 feet. Required setback from building foundations: 10 feet for drywells and 20 feet for inﬁltration trenches. Because of clogging problems, inﬁltration trenches and drywells should never be used to inﬁltrate runoff from drainage areas that are not completely stabilized. For best performance, contractors, should avoid compaction of soils around trenches and dry wells during construction. Additional information Massachusetts Stormwater Management Policy: Volume Two: Stormwater Technical Handbook; MA DEP & MA CZM; 1997 Maintenance After construction, inspect after every major storm for the ﬁrst few months to ensure stabilization and proper function. On a monthly basis, remove sediment and oil/grease from pretreatment devices, overﬂow structures, and the surface of inﬁltration trenches. Semi-annually, check observation wells 3 days after a major storm. Failure to percolate within this time period indicates clogging Semi-annually, inspect pretreatment devices and diversion structures for sediment build-up and structural damage. If ponding occurs on the surface of an inﬁltration trench, remove and replace the topsoil or ﬁrst layer of APPENDIX E EROSION CONTROL REPORT Lakeview Subdivision Preliminary Erosion Control Report EROSION CONTROL REPORT A comprehensive (SWMP) Erosion and Sediment Control Plan (along with associated details) will be included with the final construction drawings. It should be noted, however, that any such Erosion and Sediment Control Plan serves only as a general guide to the Contractor. Staging and/or phasing of the BMPs depicted, and additional or different BMPs from those included may be necessary during construction, or as required by the authorities having jurisdiction. It shall be the responsibility of the Contractor to ensure erosion control measures are properly maintained and followed. The Erosion and Sediment Control Plan is intended to be a living document, constantly adapting to site conditions and needs. The Contractor shall update the location of BMPs as they are installed, removed or modified in conjunction with construction activities. It is imperative to appropriately reflect the current site conditions at all times. The Erosion and Sediment Control Plan shall address both temporary measures to be implemented during construction, as well as permanent erosion control protection. Best Management Practices from the Volume 3, Chapter 7 – Construction BMPs will be utilized. Measures may include, but are not limited to, silt fencing along the disturbed perimeter, gutter protection in the adjacent roadways and inlet protection at existing and proposed storm inlets. Vehicle tracking control pads, spill containment and clean-up procedures, designated concrete washout areas, dumpsters, and job site restrooms shall also be provided by the Contractor. Grading and Erosion Control Notes can be found on Sheet C001 of the Utility Plans. The Final Plans will contain a full-size Erosion Control sheet as well as a separate sheet dedicated to Erosion Control Details. In addition to this report and the referenced plan sheets, the Contractor shall be aware of, and adhere to, the applicable requirements outlined in the Development Agreement for the Lakeview Subdivision development. Also, the Site Contractor for this project will be required to secure a Stormwater Construction General Permit from the Colorado Department of Public Health and Environment (CDPHE), Water Quality Control Division – Stormwater Program, prior to any earth disturbance activities. Prior to securing said permit, the Site Contractor shall develop a comprehensive StormWater Management Plan (SWMP) pursuant to CDPHE requirements and guidelines. The SWMP will further describe and document the ongoing activities, inspections, and maintenance of construction BMPs. MAP POCKET C500 – DRAINAGE EXHIBIT ELEC WV WV H Y D H Y D CABLE VAULT CONTROL IRR T C C CT C T C S S T T T T F E S B2 4.70 �� EXISTING CHURCH BUILDING B1 2.84 �� B3-2 6.18 �� B3-1 2.85 �� OS1 0.52 �� B3-3 1.96 �� LOT 22 LOT 21 LOT 20 LOT 19 LOT 18 LOT 17 LOT 16 LOT 15 LOT 14 LOT 13 LOT 12 LOT 11 LOT 10 LOT 9 LOT 8 LOT 7 LOT 2 LOT 1 LOT 24 LOT 25 LOT 26 LOT 27 LOT 28 LOT 29 LOT 30 LOT 31 LOT 32 LOT 33 LOT 34 LOT 35 LOT 36 LOT 37 LOT 38 LOT 39 LOT 40 LOT 41 TRACT C U&AE TRACT A LOT 42 B2 OS1 EXTENDED DETENTION BASIN/ DETENTION POND 100-YR VOLUME: 4.39 AC-FT 100-YR WSEL: 4967.43 40-HOUR WQ RELEASE OS2 0.19 �� LOT 133 OWNER: ROSCHKE FAMILY TRUST LOT 132 OWNER: KLINEDINST, NICHOLAS J/TARA C EASTBOROUGH LOT 131 OWNER: JORISSEN, DAVID W WILBUR, WENDY P TRACT A OWNER: CITY OF FORT COLLINS LOT 111 OWNER: HOLMES, RICHARD L/ SHARON M LOT 110 OWNER: VANDER WILT, DOUGLAS W/ LOIS K LOT 109 OWNER: DU CHATEAU, PAUL C/SARA J LOT 108 OWNER: GRIDER, DAN A, THE WILD ROSE REVOCABLE TRUST LOT 106 OWNER: LEWIS, ANDREW/ S JUANETTE ELDORADO SPRINGS SECOND FILING LOT 105 OWNER: BACKES, KARI K LOT 104 OWNER: RICHARDSON, DONALD L/ MARILYN J LOT 6 OWNER: MT. VERNON INVESTMENT GROUP LLC LOT 7 OWNER: RAVENSCHLAG, RALPH W/ CHERYL E SILVERWOOD VILLAGE SECOND FILING LOT 8 OWNER: KENNING, MARK R/ DIANE L LOT 9 OWNER: BEANER, ROGER W/ JOANN E LOT 10 OWNER: PELKEY, SCOTT HOWE, CHARLES B3-1 B1 B3-3 OS2 OS1 LOT 112 OWNER: CALE, GARY S. SILVERWOOD VILLAGE FIRST FILING ELDORADO SPRINGS SECOND FILING LOT 5 LOT 6 LOT 4 LOT 3 CHRIST CENTER COMMUNITY CHURCH TRACT B UTILIY, ACCESS & DRAINAGE EASEMENT LOT 22 LOT 23 100' OVERFLOW N�. R��: B�: D��: REVIEWED BY: R. B�� DESIGNED BY: DRAWN BY: SCALE: DATE: NOVEMBER 2013 PROJECT: 665-002 S�� O�26S�� LAKEVIEW SUBDIVISION T�� N�� E�� S��, I��. �� P�� E�� N�� E�� S��, I��. NOT FOR CONSTRUCTION REVIEW SET 08/21/13 200 S�� C�� A��, S�� 010 F�� C��, C�� 80524 E N G I N E E R I N G � � � � � � �� PHONE: 970.221.4158 FAX: 970.221.4159 ��.��.�� DR1 DRAINAGE EXHIBIT A. B�� A. B�� 1"=50' NORTH ( IN FEET ) 1 �� = ��. 50 0 50 F�� 50 100 150 LEGEND: 4953 PROPOSED CONTOUR 93 PROPOSED STORM SEWER PROPOSED SWALE EXISTING CONTOUR PROPOSED CURB & GUTTER NOTES: PROPOSED INLET A DESIGN POINT FLOW ARROW DRAINAGE BASIN LABEL BASIN DESIGNATION BASIN AREA (AC) DRAINAGE BASIN BOUNDARY FOR DRAINAGE REVIEW ONLY NOT FOR CONSTRUCTION 1.REFER TO THE "PRELIMINARY DRAINAGE REPORT FOR REGENCY LAKEVIEW' BY NORTHERN ENGINEERING, DATED AUGUST 21, 2013 FOR ADDITIONAL INFORMATION. B2 1.45 �� D�� D�� D�� D�� D�� D�� APPROVED: CHECKED BY: CHECKED BY: CHECKED BY: CHECKED BY: CHECKED BY: C�� E�� W�� & W�� U�� S�� U�� P�� & R�� T�� E�� E�� P�� C�� F�� C��, C�� UTILITY PLAN APPROVAL CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU DIG, GRADE, OR EXCAVATE FOR THE MARKING OF UNDERGROUND MEMBER UTILITIES. CALL UTILITY NOTIFICATION CENTER OF COLORADO K�� '��. C�� . R BASIN B POND SUMMARY VOLUME REQ'D (��-��) VOLUME PROVIDED (��-��) POND INVERT 100-YEAR WATER SURFACE POND SPILL ELEV. BASIN B 4.39 4.69 4960.75 4967.43 4967.70 DRAINAGE SUMMARY TABLE DESIGN POINT BASIN ID TOTAL AREA (��) C2 C100 2-�� T� (��) 100-�� T� (��) Q10 (��) Q100 (��) B1 B1 2.84 0.53 0.66 17.0 14.1 2.62 12.57 B2 B2 4.70 0.80 1.00 11.5 6.5 7.87 43.80 B3-1 B3-1 2.85 0.63 0.79 11.8 9.3 3.77 18.12 B3-1 B3-2 6.18 0.58 0.73 14.9 13.4 6.81 31.08 B3-3 B3-3 1.96 0.28 0.34 13.4 12.7 1.07 4.75 OS1 OS1 0.52 0.22 0.28 9.3 9.0 0.27 1.2 OS2 OS2 0.19 0.15 0.19 7.1 7.0 0.13 0.32 stone and the top layer of ﬁlter fabric. Upon failure, perform total rehabilitation of the trench or dry well to maintain storage capacity within 2/3 of the design treatment volume and 72-hour exﬁltration rate. Cost Inﬁltration trenches and dry wells are moderately expensive to construct. Because trenches and dry wells can inﬁltrate stormwater closer to the source, conveyance structures such as swales and pipes can be downsized. It is important that developers and property owners provide a budget for maintenance activities, since lack of maintenance is the primary cause for premature failure of inﬁltration structures. This publication is one component of the Massachusetts Low Impact Development Toolkit, a production of the Metropolitan Area Planning Council, in coordination with the I-495 MetroWest Corridor Partnership, with ﬁnancial support from US EPA. The Massachusetts Low Impact Development Interagency Working Group also provided valuable input and feedback on the LID Toolkit. FOR MORE INFORMATION, VISIT: WWW.MAPC.ORG/LID AND WWW.ARC-OF-INNOVATION.ORG. Above: Precast concrete drywell inserts prior to installation. Photo: Lower Columbia River Estuary Partnership 11/19/201312:40 PM D:\Projects\665-002\Drainage\Detention\ 665-002__Detention Pond_SWMM Final ROB.xlsm\Stage_Storage Survey Area Data: Version 7, May 1, 2009 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Apr 22, 2011—Nov 18, 2011 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Hydrologic Soil Group—Larimer County Area, Colorado (Lakeview Hydrologic Group) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/29/2013 Page 2 of 4 B3-1 B1&B3-1 No 0.58 0.58 0.73 205 2.00% 11.0 11.0 7.9 950 1.20% 2.19 7.2 18.3 18.3 15.2 B3-1 B1,B3-1 & B3-2 No 0.58 0.58 0.73 205 2.00% 11.0 11.0 7.9 950 1.20% 2.19 7.2 18.3 18.3 15.2 OS1 OS1 No 022 022 028 45 11 10% 49 49 46 368 0 50% 141 43 93 93 90 TIME OF CONCENTRATION COMPUTATIONS Gutter Flow 1 Design Point Basin Overland Flow R. Banning November 19, 2013 Time of Concentration (Equation RO-4)  3 1 1 . 87 1 . 1 * S Ti C Cf L   OS1 OS1 No 0.22 0.22 0.28 45 11.10% 4.9 4.9 4.6 368 0.50% 1.41 4.3 9.3 9.3 9.0 OS2 OS2 No 0.15 0.15 0.19 20 23.50% 2.8 2.8 2.7 368 0.50% 1.41 4.3 7.1 7.1 7.0 B Overall B Overall No 0.60 0.60 0.76 210 1.90% 10.8 10.8 7.5 1150 1.50% 2.45 7.8 18.7 18.7 15.4 * Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins. 11/19/2013 12:36 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Tc B1 2.838 0.671 0.288 0.034 0.367 0.000 Sandy | Average 2% to 7% 1.478 0.53 0.53 0.66 45% B2 4.704 3.799 0.023 0.000 0.000 0.000 Sandy | Average 2% to 7% 0.882 0.80 0.80 1.00 81% B3-1 2.85 0.65 0.33 0.02 0.73 0.00 Sandy | Average 2% to 7% 1.115 0.63 0.63 0.79 57% B3-2 6.18 0.90 0.72 0.06 1.68 0.00 Sandy | Average 2% to 7% 2.813 0.58 0.58 0.73 50% B3-3 1.96 0.00 0.03 0.01 0.27 0.00 Sandy | Average 2% to 7% 1.650 0.28 0.28 0.34 14% B1&B3-1 5.69 1.32 0.62 0.06 1.09 0.00 Sandy | Average 2% to 7% 2.592 0.58 0.58 0.73 51% B1,B3-1 & B3-2 11.87 2.23 1.34 0.12 2.77 0.00 Sandy | Average 2% to 7% 5.406 0.58 0.58 0.73 50% B1,B3 13.83 2.23 1.37 0.13 3.05 0.00 Sandy | Average 2% to 7% 7.056 0.54 0.54 0.67 45% OS1 0.52 0.05 0.00 0.00 0.00 0.00 Sandy | Average 2% to 7% 0.473 0.22 0.22 0.28 9% OS2 0.19 0.00 0.00 0.00 0.00 0.00 Sandy | Average 2% to 7% 0.195 0.15 0.15 0.19 0% B Overall 18.54 6.03 1.39 0.13 3.05 0.00 Sandy | Average 2% to 7% 7.938 0.60 0.60 0.76 54% EXISTING TOTAL 19.25 4.70 0.34 0.19 0.62 0.00 Sandy | Average 2% to 7% 13.396 0.39 0.39 0.49 29% TOTAL AREA 19.25 6.08 1.39 0.13 3.05 0.00 Sandy | Average 2% to 7% 8.605 0.59 0.59 0.74 53% 1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS November 19, 2013 Composite Runoff Coefficient with Adjustment 11/19/2013 12:37 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Composite Runoff Coefficient