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Home My WebLink AboutTHE LOFTS AT PARK CENTRAL - PDP - 28-02A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTjhef*%AR drauoew -(w 1W46-02o. *rwo LW4* j% sko 6&tra(aw mp ib �p�dr�c 0e. flo rmp r p or r 45A t4 �Yd fv Ih l 1 I some Si D VICINITY MAP NTS I I 1 i 1 I i ►. 9QW1130.4 7 VICINITY MAP ►U 1 6. I CONCLUSIONS 6.1 Compliance with Standards All computations that have been completed within this report are in compliance with the Chapter 10 of the City of Fort .Collins Code, City of Fort Collins Erosion Control Reference •Manual for Construction Sites and the Storm Drainage Design Criteria Manual. Requirements placed on the site related to the Master Plan Update have been followed. 6.2 Drainage Concept The proposed drainage concepts presented in this report and on the construction plans adequately provide for stormwater quality treatment of existing and proposed impervious areas. Conveyance elements have been designed to pass required flows and to minimize future maintenance. If, at the time of construction, groundwater is encountered, a Colorado Department of Health Construction Dewatering Permit will be required. REFERENCES 1. City of Fort Collins, "Storm Drainage Criteria Manual", (SDCM), dated March, 1986. 2. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria Manual", Volumes 1 and 2, dated March, 1969, and Volume 3 dated September, 1992. 3. "Hydraulic Modeling of the Spring Creek Basin" by Anderson Consulting Engineers, Inc. dated February 15, 2002. 4. "Spring Creek Basin Hydrologic Model Update" by Anderson Consulting Engineers, Inc. revised December 8, 1999. f►1 into the inlet will reach the water quality pond via the existing and rerouted storm sewer o system. Any flows in excess of the inlet's capacity will overtop to the south into Basin 4. Basin 4 includes the southeast portion of the existing Fort Collins Club parking lot as ' well as the proposed expansion and reconfiguration of the south portion of this lot. This basin drains to the south to a new proposed inlet and storm sewer system which will take ' the runoff under the Spring Creek Trail. 4.3 Drainage Summary Drainage facilities located outside of the right of way (including the water quality pond, existing and proposed storm drain system and the pond outlet) will be maintained by the owners of the site. 5. EROSION CONTROL 5.1 General Concept ' This site lies within the Moderate Rainfall and Wind Erodibility Zone per the City of Fort Collins Zone Maps. The potential exists for silt movement from the site and into Fossil ' Creek. Potential also exists for tracking of mud onto existing streets which could then wash into existing storm systems. The erosion control escrow amount is $9,345. 1 5.2 Specific Details To limit the amount of silt leaving the site several erosion control measures shall be implemented during construction. All inlets shall be protected with gravel filters, straw ' bales will be used where appropriate, and the south and west boundaries shall have silt fence installed. Vehicle tracking pads shall be installed at both connections to the existing private drive to control the mud being tracked onto the existing pavement. During overlot grading, disturbed areas are to be kept in a roughened condition and watered to reduce wind erosion. [4 I 4. DRAINAGE FACILITY DESIGN 4.1 General Concept All of the runoff from this site and the adjacent areas drains south to Spring Creek via gutters, storm pipes, and overland flow. The majority of this site and the adjacent parking areas will be routed to the water quality pond. This pond will be incised into the bank of Spring Creek and will have a water quality outlet structure mounted in a headwall. There will be no pipe outlet for the pond. The wall will overtop in larger storms and will drain overland to the creek. Approximately the southern half of the site is in the floodplain. All structures are elevated to be protected in the 100 year flood. 4.2 Specific Flow Routing A summary of the drainage patterns within each basin is provided in the following paragraphs. Basin 1 includes the most northwesterly building and the private drive and commercial building west of the site. This basin drains to an existing 4' inlet which will remain. This inlet was calculated to have less capacity than the 100 year runoff from the basin. Flows that go into the inlet will reach the water quality pond via the existing and rerouted storm sewer system. Any flows in excess of the inlet's capacity will overtop to the south, travel down the existing private drive to Spring Creek. Basin 2 includes the majority of the improvements to the site. Six multi -family buildings and associated parking are proposed within this basin. This basin drains south to a proposed inlet and storm sewer which conveys the flows to the water quality pond. Basin 3 includes the northeast portion of the existing Fort Collins Club parking lot. The only improvements proposed in this basin are the reconfiguration of parking islands and drives. This basin drains to an existing 4' inlet which will remain. This inlet was calculated to have less capacity than the 100 year runoff from the basin. Flows that go 5 This project complies with the requirements of Chapter 10 of the City Code. Constraints on the site include the "no fill" requirement for the floodway and that all proposed buildings in the floodplain will be elevated 1.5' minimum above the 100 year Base Flood ' Elevation. 3.3 Hydrologic Criteria Runoff computations were prepared for the 10-year minor and 100-year major storm frequency utilizing the rational method. tAll hydrologic calculations associated with the basins are included in Appendix B of this report. Standard Form 8 (SF-8) provides time of concentration calculations for all sub - basins. Standard Form 9 (SF-9) provides a summary of the design flows for all Sub - basins and Design Points associated with this site... ' Water quality volume was calculated using the method recommended in the "Urban Storm Drainage Criteria Manual". 3.4 Hydraulic Criteria ■ All hydraulic calculations within this report have been prepared in accordance with the City of Fort Collins Drainage Criteria and are included in Appendix C of this report. The existing storm sewer system's reconfiguration was analyzed with this report. The inlets on the existing system do not take the entire 100 year flow (Design Points 1 and 3), but both of these areas will overflow to the south and will not jeopardize any structures. With this project and the reconfiguration of the parking areas; less flow will be routed to the existing system than the present day flows. One inlet is being removed, and less area is flowing to the other inlets on the existing system. All of the storm sewers (existing and proposed) are surcharged with the 100 year base flood in Spring Creek. All buildings are elevated 1.5' above this elevation to protect the structures. Because of this, the storm sewer systems were designed based on a free outfall. All of the sumps (existing and proposed) have areas that can overflow if necessary without damage to structures. 4 I off site flows that enter the property are the commercial building and private drive adjacent to the northwest portion of the site which drain to the existing storm sewer system and the easterly portion of the Fort Collins Club parking lot which also drains to this system. Both of these areas were analyzed in this report. In the Spring Creek Master Plan, this site is in basin 219. Conveyance element 520 represents Spring Creek through the site. 3. DRAINAGE DESIGN CRITERIA 3.1 Regulations This report was prepared to meet or exceed the "City of Fort Collins Storm Drainage Design Criteria Manual" specifications. Where applicable, the criteria established in the "Urban Storm Drainage Criteria Manual" (UDFCD), 1984, developed by the Denver Regional Council of Governments, has been used. This project complies with the requirements of Chapter 10 of the City Code. 3.2 Development Criteria Reference and Constraints The runoff from this site has been routed to conform to the requirements of the City Stormwater Department. Detention is not proposed for this site. The peak flow from the Master Plan is 48 minutes at Conveyance Element 520 in the SWMM Model. Runoff from this site peaks at 5 to 6 minutes and will be off of the site prior to the Creek's peak. This is shown in the hydrologic calculations in Appendix B and the SWMM Model in Appendix F. Water Quality is required for the new construction proposed on the site. This requirement is only for the area that will have new buildings constructed. The reconfiguration of the parking area and trail required the rerouting of portions of the existing storm sewer system. This system only takes flows from the existing parking areas and the commercial building northwest of the project. Additional volume was designed in the water quality pond to treat the runoff from the majority of the existing parking. This is over and above the requirements for the project. Only the most southwest portion of the parking will not be treated. The water quality pond will be in the floodway, but will be completely below the existing ground in the area. 3 J 1 2. I I I The Spring Creek Floodplain encroaches into approximately the southern half of the proposed development. The Floodway is on the site, but south of most of the proposed improvements. The only improvements in the Floodway that are proposed are additional parking and the rerouting of a portion of the Spring Creek Trail. All of this work will "cut" within the floodway. No fill of any kind is proposed in the floodway. No buildings are proposed in the floodway. Four of the proposed multi -family buildings are in the City floodplain. All of these buildings will be elevated so that the lowest floor (garage) is 1.5' above the floodplain elevation. Building foundations will be slab on grade. See the Grading Plan and the Drainage and Erosion Control Plan for specific information related to the building elevations. These buildings will require a Floodplain Use Permit at time of Building Permit application. They will also require a FEMA Elevation Certificate prior to issuance of Certificates of Occupancy. See Appendix F in this report for information related to the Floodplain. The following table lists the elevations requirements for these 4 buildings: BLDG 3 BLDG 4 BLDG 5 BLDG 6 City 100 Year Base Flood Elevation 4940.2 4939.6 4940.2 4939.8 Regulatory Flood Protection Elevation 4941.7 4941.1 4941.7 4941.3 Proposed Lowest Floor Elevation (Garage) 4941.7 4941.3 4941.7 4941.3 Proposed HVAC Elevation 4941.7 4941.3. 4941.7 4941.3 DRAINAGE BASINS AND SUB -BASINS 2.1 Major Basin Description The proposed development lies within the Spring Creek Master Drainage Basin. The . Updated Master Drainage Plan for this Basin has been completed by. Anderson Engineering Consultants, Inc. Portions of this report are in Appendix F.. The 100-year floodplain and the floodway from the updated report are reflected in the plans for this proj ect. 2.2 Sub -basin Description This site drains to Spring Creek independent of any of the surrounding land. The only 2 u I I I _l 1. GENERAL LOCATION AND DESCRIPTION 1.1 Location Park Central Residential Subdivision is located in east central Fort Collins. This project is located in the Northwest Quarter of Section 19, Township 6 North, Range 69 West of the Sixth Principal Meridian, in the City of Fort Collins, Larimer County, Colorado. See the location map in Appendix A. The project is located in the southeast of Prospect Road and Lemay Avenue. The project is bounded on the north by Prospect Road, on the east by the Fort Collins Health Club and its parking lots, on the south by Spring Creek and on the west by a private drive accessing this site and the commercial area to the west. 1.2 Description of Property The entire project consists of approximately 6 acres of land in two separate parcels. The property includes all of Spring Creek from Lemay to the west side of the Fort Collins Club building as well as the majority of the Fort Collins Club's parking. Only 2 acres are proposed for new buildings and the parking lots will be reconfigured with the project. There is an existing storm sewer system through this site for larking lot drainage. A portion of this system will be reconstructed to provide Water Quality for a portion of the existing parking and also to reconfigure the parking area. The land currently slopes to the south at a range of approximately 1 % to 4%. Spring Creek is located on the southerly portion of the site. Spring Creek has a floodplain and floodway mapped by both the City and FEMA. The City mapping has recently been completed and is documented in the "Hydraulic Modeling of the Spring Creek Basin" by Anderson Consulting Engineers, Inc. dated February 15, 2002; and in the "Spring Creek Basin Hydrologic Model Update" by Anderson Consulting Engineers, Inc. revised December 8, 1999. Excerpts of these reports are in Appendix F. The City floodplain is considerably higher than the current FEMA floodplain. It is our understanding that the City will eventually have the FEMA maps revised with the new data. This report only addresses issues related to the City Floodplain because it is significantly higher than FEMA. This was done to eleiminate the confusion of discussing 2 different floodplains when the City's controls the development requirements of the site. t 0 I TABLE OF CONTENTS ' TABLE OF CONTENTS............................................................................................................... iii 1. GENERAL LOCATION AND DESCRIPTION ' 1.1 Location...................................................................................................................1 1.2 Description of Property ............................................................................................1 ' 2. DRAINAGE BASINS AND SUB -BASINS 2.1 Major Basin Description..........................................................................................2 2.2 Sub -Basin Description.............................................................................................2 3. DRAINAGE DESIGN CRITERIA ' 3.1 Regulations..............................................................................................................3 3.2 Development Criteria Reference and Constraints....................................................3 3.3 Hydrologic Criteria..................................................................................................4 ' 3.4 Hydraulic Criteria....................................................................................................4 4. DRAINAGE FACILITY DESIGN 4.1 General Concept.......................................................................................................5 4.2 Specific Flow Routing.............................................................................................5 4.3 Drainage Summary ...................................................................................................6 5. EROSION CONTROL 5.1 General Concept......................................................................................................6 ' 5.2 Specific Details..........................................:.............................................................6 ' 6. CONCLUSIONS 6.1 Compliance with Standards....................................................................................7 6.2 Drainage Concept.....................................................................................................7 7. REFERENCES....................................................................................................................7 ' APPENDICES A Vicinity Map ' B Hydrologic Computations C Hydraulic Calculations D Water Quality Pond Sizing E Erosion Control Calculations F Floodplain Information IG Figures and Tables iii i� North Star rl*am., design, inc. I I IJuly 30, 2002 Basil Hamdan ICity of Fort Collins Stormwater 700 Wood Street Fort Collins, CO 80522-0580 RE: Final Drainage and Erosion Control Study for Park Central Residential ' Dear Basil, I am pleased to submit for your review and approval, this revised Final Drainage and Erosion Control Study for Park Central Residential, a multi -family residential project. I certify that this report for the drainage design was prepared in accordance with the criteria in the City of Fort Collins Storm Drainage Manual. II appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. Sincerely, 288 �m' 9 %Q OI0 Q Michael Oberlander, P.E., L.S.I. Fss/pNALEN�'�� ' 700 Automation Drive, Unit I Windsor, Colorado 80550 970-686-6939 Phone 970-686-1188 Fax FINAL DRAINAGE AND EROSION CONTROL STUDY PARK CENTRAL RESIDENTIAL Prepared for: Park Central, LLC 2642 Midpoint Drive, Unit A Fort Collins, CO 80525 Prepared by: North Star Design 700 Automation Drive, Unit I Windsor, Colorado 80550 (970) 686-6939 July 30, 2002 Job Number 174-01