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Home My WebLink AboutPOUDRE SCHOOL DISTRICT, 2003 ELEMENTARY SCHOOL - SITE PLAN ADVISORY REVIEW - 5-02 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT` NCUTE Preliminary Drainage & BEYOND ENG IN EERING Erosion Control Study 2003 Elementary School — Timberline Site APPENDIX • Developed Hydrology • Street Capacity and Inlet Design • Storm Sewer Design • Detention/Water Quality Pond Design • Design Charts, Tables and Graphs • Supplemental Information From Others BACK POCKET — Overall Drainage Plan - Timbers P.U.D. Developed Drainage Plan a Nolte Associates, Inc. 12 N:\FC01950rainageTC019501_DmgRpt.doc NC&TE Preliminary Drainage & BEYOND ENGINEERING Erosion Control Study 2003 Elementary School — Timberline Site 1. Storm Drainage Criteria and Construction Standards Manual. City of Fort Collins Stormwater Utility, Colorado, May 1984. 2. Urban Storm Drainage Criteria Manual, Denver, Colorado, prepared by Wright - McLaughlin Engineers, March 1969. 3. Fossil Creek Drainage Basin — Master Drainage Plan — Final Report, prepared for City of Fort Collins, prepared by Simons Li and Associates, Inc., August 1982. 4. Final Drainage Report for Timbers PUD, prepared by TST Consultants, Inc., November 16, 2001. 5. Final Drainage Report for Westchase PUD, prepared by David Evans and Associates, Inc., last revision: November 3, 2000. 6. Geotechnical Enzineering Report, Proposed 2003 Elementary School, Northeast Corner of Timberline Road and Timber Trail Road, Fort Collins. Colorado, prepared by Terracon, November 9, 2001. Nolte Associates, Inc. I I N:\FC0195\Drainage\FC019501_DmgRpt.doc NCLTE Preliminary Drainage & Erosion Control Study BEYOND ENGINEERING 2003 Elementary School — Timberline Site 7.5 Construction Materials & Equipment The contractor shall store construction materials and equipment on site in such a manner that the materials and equipment will not impact Mail Creek Ditch. The Contractor shall also provide an area for maintenance and fueling of equipment in a confined area on site from which runoff will be contained and filtered prior to entering the ditch. Contaminated soils from fuel spills shall follow state and local criteria for removal. 8.0 CONCLUSIONS 8.1 Drainage Concept The proposed drainage concepts presented in this study and shown on the drainage plan adequately provide for the conveyance of developed runoff for detention and water quality purposes from the proposed development and adjacent off -site basins. Water quality will be provided via bio-swales, grass turf swales and the detention pond in the southeast comer of the Site. This ensures that the proposed development will have limited negative impact to downstream conveyance facilities under the designed storms. Nolte Associates, Inc. 10 N:\FC01950rainageTC019501 DmgRpt.doc NC437E Preliminary Drainage & BE YON D E N G IN E E a ING Erosion Control Study 2003 Elementary School — Timberline Site landscape swales, and storm sewer systems during and after grading and construction. Thus, sediment not detained by the inlet protection filters (gravel filters and straw bale barriers) will be conveyed to the detention pond, which will also act a sediment trap during construction. 7.2 Existing Site Conditions In general, the Site slopes at one percent to the south and east towards Fossil Creek and Fossil Creek Reservoir. The Site's present use is agricultural with hay as the main crop. The Mail Creek Irrigation Ditch traverses along the eastern property line of the parcel. 7.3 Soils The subsurface soils at the Site consist of an approximate 6-inch layer of cultivated silty topsoil, underlain by sandy lean clay, lean clay with sand, clayey sand and silty sand extending to the depths explored to the bedrock below. Reference the geotechnical report for more detailed information (Ref. 6). 7.4 Schedule Silt fencing will be installed first followed by clearing and grubbing and overlot grading for the Site. Next will be the placement of the vehicle tracking control at the construction entrance. The proposed utility and building construction will occur next. Inlet protection will be installed during the construction phase of the landscape storm sewer. Prior to the final grading and landscaping, erosion control matting will be installed at curb cuts and storm sewer outlet locations. Paving and landscaping will follow subsequently. After permanent vegetation is stabilized, the inlet protection as well as the silt fence will be removed. The estimated start of construction for the site has been set for May, 2002 and completion to be one year later. The school is scheduled to open in the Fall of 2003. Nolte Associates, Inc. 9 N:\FC0195\Drainage\FC019501 DmgRpt.doc Preliminary Drainage & 6 E VON 0 E N G IN E E R ING Erosion Control Study 2003 Elementary School — Timberline Site 6.0 STORM SEWER SYSTEMS 6.1 General Concept There are two storm sewer systems, one running across the north side of the school and the other along the southern border of the Site. The system to the north, System 200, captures flows from design points 400, 401, and 200-204. The main reach of pipe will be 30" HDPE ADS N-12 running at 0.50%. This pipe has no "wet" utility crossings. The system outfalls into the detention pond located in the southeast comer of the Site. The system to the south is designated as System 300. This system begins with a connection to the existing 18" RCP under Timberline Road. The runoff collected at design points 402, and 300-303 are conveyed by HDPE ADS N-12 pipe east to the detention facility. At the entrance to the visitor parking lot RCP will be installed to protect the integrity of the system. Roof drainage is collected within the school and routed to the connection points designated by DP 100 and 101. HDPE ADS N-12 pipe will route the flows south to a manhole intersecting System 300 7.0 EROSION AND SEDIMENT CONTROL 7.1 General Concept Erosion control during construction of this project will consist of silt fencing installed around the Site's disturbed areas that will be graded and have the potential for sediment to be transported off the Site. The Grading and Erosion Control Plan in the construction drawings (see back pocket) indicates the type and timing of proposed measures. Once the foundation is in place and floor slabs constructed, the potential for erosion will be minimized. Generally, developed storm flows will travel to the detention/water quality pond via curb and gutter, Nolte Associates, Inc. 8 N:\FC0195\DIainage\FC019501_DmgRpt.doc Preliminary Drainage & 9 E Y O N 0 E N G I N E E R I N G Erosion Control Study 2003 Elementary School — Timberline Site 5.3 Detention/Water Quality Pond Design The water quality pond for the 11.43-acre Site uses the affected developed areas of 12.13 acres. The area to the north (5.05 ac) is not being developed at this time. The water quality pond was designed using Urban Storm Drainage Criteria Manual Volume 3 — Best Management Practices (BMPs) "Design Procedure Form: Extended Detention Basin (EDB)", (See Appendix D). The required 100-yr detention volume was calculated using the FAA method. Utilizing the Urban Drainage software, Hydropond, a volume of 0.761 ac-ft is needed. The water quality capture volume (WQCV) is based on the tributary area draining to the pond as well as the percentage of the total area that is impervious. The Site has an imperviousness ratio of 49%. This includes all impervious areas such as pavement, sidewalk, and rooftop compared to the landscaped areas. A WQCV of 0.247 ac-ft will be required, based on calculations obtained from the Urban Drainage manual. The total volume required is 1.008 ac-ft, the actual volume for the proposed detention pond is 2.750 ac-ft. These calculations can be found in Appendix D. Detention requirements for developing the school site have been modified based in the drainage criteria presented in the Final Drainage Reports for the Timbers and Westchase PUDs. Based on these reports, a release rate of 25.1 cfs was determined for the school site and the remaining undeveloped parcel (off -site basin 401) to the north. Runoff from the east half of the full width of Timberline Road and north half of the proposed Timber Trail Road will also be conveyed to the detention pond and to be released at the above rate. Nolte Associates, Inc. 7 N.\FC0195\Dminage\FC019501_DmgRpt.doc Nc� Preliminary Drainage & BE Y O N D E N G IN E E R I N G Erosion Control Study 2003 Elementary School - Timberline Site points collect the stormwater. Basin 203 (0.65 ac) and 204 (1.03 ac) slope to the north across playing fields at mild slopes around 2%. Low points within the basin collect the runoff in area inlets. The inlet at design point 203 will have a stub out ,■ allowing for future development to tie into this system from the north. Basin 205 (1.22 ac) is comprised of a playing field and the detention pond. Runoff from Basin 300 (0.61 ac) encompasses the southern parking lot that will be used for visitor parking and parent drop-off. Stormwater will traverse the site over pavement to curb and gutter routing the water to a 5' Type `R' inlet. Basins 301 (1.63 ac) and 303 (0.64 ac) attenuate runoff to an inlet at design point 301. The from Basin 302 flows to the runoff (1.18 ac) sheet south across the playground area, which consists of sand, wood chips, and grass. This runoff is collected in an area inlet at DP 302. Flows collected at DP301 enter this inlet from 3. the south. These flows are then routed to the east to the pond. Basin 304 (0.38 ac) attenuates the half -street runoff from Timber Trail Road at an existing 5' Type `R' inlet. The inlet is adequately sized for the change in basin boundary created by r; development of the Site. The off -site basins are designated as the 400-series. Basin 400 (1.66 ac) encompasses the half street flows from Timberline Road and routes runoff to a 10' Type `R' inlet, which will outfall to DP 400. Basin 401 (5.05 ac +/-) is the undeveloped area bordering the Site to the north. Basin 402 has limited information regarding drainage. An existing 18" CMP crosses under Timberline Road. For design purposes it is assumed the pipe is flowing at full capacity calculated using the Manning's equation. Nolte Associates, Inc. 6 N:\FC0195\Drainage\FC019501_DmgRpt.doc Preliminary Drainage & BE YON D E N G IN E E R ING Erosion Control Study 2003 Elementary School — Timberline Site 5.0 DEVELOPED DRAINAGE CONDITIONS 5.1 General Concept In general, developed flows from the proposed site improvements will sheet flow or be conveyed via two storm pipe systems in an easterly direction to the proposed on -site detention/water quality pond. Developed flows along the Site's west side and along the future improvements of Timberline Road will flow north via curb and gutter to a proposed inlet at the street's low point. In an effort to achieve environmental sustainability, bio-swale systems are being considered in some locations within the site. These swales are not designed for particular storm levels but rather for areas of opportunity to capture concentrated oil, salt, sand and other pollutants left by automobiles. In, addition, a porous pavement alternative (GravelPave) for the faculty parking lot will be a construction bid alternate to the typical asphalt pavement. 5.2 Basin Descriptions Basin 100 is the rooftop of the school (1.17 ac). Stormwater that collects on the school rooftop will sheet flow to drains located toward the center of the roof. The mechanical engineer has designed the roof drains and piping. This water will be piped to the center of the building and'route flows to the south of the building. Storm pipes will pickup these flows and continue to route the stormwater to the detention pond. Basin 200 (1.47 ac) incorporates the west entrance drive, faculty parking and bus drop-off. The developed runoff from Basin 200 flow overland through landscaped areas before entering paved areas where the water will sheet flow within the proposed curb and gutter systems to a 10' Type `R' inlet. Basin 201 (0.09 ac) and 202 (0.38 ac) border the building to the north. Area inlets located within local low Nolte Associates, Inc. 5 N:\FC0195\Drainage\FC019501_DmgRpt.doc NcCTE Preliminary Drainage & B E Y ON D E N G IN E E R ING Erosion Control Study 2003 Elementary School — Timberline Site Proposed Timber Trail Road that will border the Site to the south has been designed TST Consultants as part of the construction plans for the Timbers PUD and meets the street cross section equivalent to City of Fort Collins' 2-lane minor collector street (76-ft R-O-W). There will be a 30-foot wide entrance to the Site on Timber Trail Road to provide for parent drop-off and visitor parking. 3.0 METHODOLOGY 3.1 Compliance with Standards The following Preliminary Drainage & Erosion Control Study was prepared in accordance with the design requirements and procedures set forth in the City of Fort Collins (City) Storm Drainage Criteria and Construction Standards (Criteria — Ref. 1) and Urban Storm Drainage Criteria Manual (Manual — Ref. 2) by the Urban Drainage and Flood Control District. 3.2 Analytical Methods The Rational Method was used to calculate 10 and 100-year developed flows. The Rational Method is widely accepted for design problems involving small drainage areas (<160 acres) and short times of concentration. Mathematically, it relates peak discharge to the runoff coefficient, rainfall intensity, and drainage area. Runoff coefficients and rainfall intensity data were obtained from the. Criteria. 4.0 HISTORIC DRAINAGE BASINS 4.1 Major Basin Description The Site lies within the Fossil Creek Reservoir Drainage Basin watershed. A master drainage study does not exist for this portion of the basin. However, topography shows that this site drains to Fossil Creek Reservoir. Per this report, the historic land use is agricultural and proposed land use as low density mixed use (LDMU). Nolte Associates, Inc. 4 N:TC019SDrainageTC019501_DmgRpt.doc II NC&TE Preliminary Drainage & BEY ON D E N GIN E E R ING Erosion Control Study 2003 Elementary School — Timberline Site will be a 36-foot wide entrance to the Site on Timberline Road to provide for bus access and faculty parking. 2.0 VICINITY MAP P&ted from TOP01 i Nolte Associates, Inc. 3 N:\FC0195\Drainage\FC019501 DmgRpt.doc i NJ C &�M Preliminary Drainage & B E VON D E N G I N E E a I N G Erosion Control Study 2003 Elementary School — Timberline Site approximate depths of 8- to 15-feet below existing site grades. The geotechnical engineering report prepared by Terracon (11/09/01) indicates that on -site subsoil conditions are suitable for the proposed construction. 1.3 Proposed Project Description The proposed development will be annexed and zoned for school use. The Fort Collins 2003 Elementary School will be modeled similar to the 2002 Prototype building. This school will provide educational resources for approximately 600 The building has 1.17 The landscape students. school a roof area of acres. areas on the west side of the school (along Timberline Road) will have berms varying in height from 2- to 4 feet. The area to the south of the school building will be the playground area. The playground areas will incorporate basketball courts (2), other hard surface playing areas such as foursquare and tetherball, a mulched area for swings and playground equipment and small sandbox play areas (refer to landscape plans). To the east of the school building and playground area will be multi -use playing fields (soccer and baseball) and a site detention facility. Timberline Road (County Road 11) is currently a 24-foot wide paved street used for local access with an existing eastern right-of-way of 40 feet. The east side Timberline Road will be widened and upgraded by the developers of Westchase and The Timbers PUD to meet the street cross section equivalent to City of Fort Collins' 4-lane arterial road. David Evans and Associates (DEA), Civil Engineers for the Westchase PUD, have designed the Timberline Road improvements that will be built at the same time as the school. Nolte has coordinated curb return information with DEA that relate to the Timberline Road construction plans. The increase to have 83-foot flowline to flowline proposed street section will an arterial street and have an increased east right-of-way width of 57.5 feet. There 1 Nolte Associates, Inc. 2 N:\FC0195\Drainage\FC019501_DtngRpt.doc Preliminary Drainage & Erosion Control Study B E YON D E N G IN E E R ING 2003 Elementary School —Timberline Site 1.0 INTRODUCTION 1.1 Site Location The proposed 2003 Elementary School site (Site) is located along Timberline Road north of the Westchase PUD and borders along the north boundary of the proposed the "Timbers PUD". The school parcel is also bounded by the Mail Creek Ditch to the east and vacant farmland to the north. More particularly, the Site (11.434 acres) is a parcel of land designated as Tract "A" of the Minor Land Division — Poudre School District And Paragon Point Partners, LTD which lies within the South Half of the Northwest Quarter of Section 8, Township 6 North, Range 68 West of the 6th Principal Meridian, County of Larimer, State of Colorado (see Vicinity Map, page 3). 1.2 Existing Site Description In general, the Site slopes at one percent to the south and east towards Fossil Creek and Fossil Creek Reservoir. The Site's present use is agricultural with hay as the main crop. The Mail Creek Irrigation Ditch traverses along the eastern property line of the parcel. Presently, the areas surrounding the proposed school site consist of farm and hay fields. However, proposed land development to the south for multi -family residences (Timbers P.U.D.) are in the final design and municipal approval process. Westchase PUD, a 408 lot single-family subdivision located south of the school site and the Timbers site, is currently under construction with the installation of utilities and roads. The existing soil conditions on the Site consist of an approximate 6-inch layer of cultivated silty topsoil, underlain by lean clay with sand, lean clay, and sandy lean clay extending to the depths explored to the bedrock below (Ref. 6). Groundwater was encountered and noted in the Site's soil boring logs to range between Nolte Associates, Inc. 1 N:\FC0195\Drainage\FC019501_DmgRpt.doc NCCTEPreliminary Drainage & BEYOND ENGINEERING Erosion Control Study 2003 Elementary School —Timberline Site APPENDIX • Developed Hydrology • Street Capacity and Inlet Design • Storm Sewer Design • Detention/Water Quality Pond Design • Design Charts, Tables and Graphs • Supplemental Information From Others BACK POCKET — Overall Drainage Plan - Timbers P.U.D. Developed Drainage Plan Nolte Associates, Inc. N:\FC0195\Drainage%FC019501_DmgRpt.doc Preliminary Drainage & Erosion Control Study BE Y O N D E N GIN E E a ING 2003 Elementary School — Timberline Site i 1.0. TABLE OF CONTENTS PAGE INTRODUCTION... ...1 1.1 Site Location ......... :............................................................................................... 1 1.2 Existing Site Description......................................................................................I 1.3 Proposed Project Description................................................................................2 2.0 VICINITY MAP...............................................................................................................3 3.0 METHODOLOGY............................................................................................................4 3.1 Compliance with Standards..................................................................................4 3.2 Analytical Methods...............................................................................................4 4.0 HISTORIC DRAINAGE CONDITIONS.........................................................................4 4.1 Major Basin Description.......................................................................................4 5.0 DEVELOPED DRAINAGE CONDITIONS....................................................................5 5.1 General Concept....................................................................................................5 5.2 Basin Descriptions................................................................................................5 5.3 Detention/Water Quality Pond Design.................................................................7 6.0 STORM SEWER SYSTEMS...........................................................................................8 6.1 General Concept....................................................................................................8 7.0 EROSION AND SEDIMENT CONTROL.......................................................................8 7.1 General Concept ................................... :................................................................ 8 7.2 Existing Site Conditions........................................................................................9 7.3 Soils...................................................................................................................9 7.4 Schedule................................................................................................................9 7.5 Construction Materials and Equipment..............................................................10 8.0 CONCLUSIONS.............................................................................................................10 8.1 Drainage Concept................................................................................................10 REFERENCES......................:........................................................................................11 Nolte Associates, Inc. N:\FC0195\DIainage\FC019501_DmgRpt.doc 2003 PROTOTYPE ELEMENTARY SCHOOL TIMBERLINE SITE PRELIMINARY DRAINAGE AND EROSION CONTROL REPORT for ............................. ............................ .............................. 2407 LaPorte Avenue Ft. Collins, Colorado 80521 by Nolte Associates, Inc. 1901 Sharp Point Drive, Suite A Fort Collins, Colorado 80525 (970) 221-2400 January 23, 2002 i