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HomeMy WebLinkAboutSTONERIDGE PUD, SECOND FILING PRELIMINARY AND FINAL - 21 92E - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL STUDY FOR STONE RIDGE P.U.D. SECOND FILING FORT COLLINS, COLORADO VI. CONCLUSIONS A. Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. B. Drainage Concept The temporary detention pond, built with the First Filing, will adequately provide for the detention of developed on -site flows from Stone Ridge Second Filing. The orifice plate in the outlet structure will have to be replaced to allow for an adjustment of the allowable release from the pond. The street conveyance system will adequately transport developed runoff from the Second Filing to the permanent and temporary channel sections. The developed storm water runoff has been controlled in order to eliminate off -site downstream damage from up to and including the 100 year storm event. The proposed drainage concepts presented in this report and shown on the drainage plan are in compliance with the City of Fort Collins drainage criteria. C. Erosion Control Concept The proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from the Stone Ridge P.U.D. Second Filing. Through construction of the proposed erosion control concepts, the City of Fort Collins performance standards will be met. The proposed erosion control concepts presented in this report and shown on the erosion control plan are in compliance with the City of Fort Collins erosion control criteria. N. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1984, Revised January 1992. 2. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991. 3. Foothills Basin (Basin G) Drainage Master Plan, Fort Collins, Colorado, by Resource Consultants, Inc. February, 1981. 4. Master Drainage Study for the Pinecone P.U.D., Fort Collins, Colorado, by RBD Inc., March 1992. 5. Final Drainage and erosion Control Study for Stone Ridge P.U.D. First Filing, Fort Collins, Colorado, by RBD, Inc. September 1992. 7 APPENDIX t I ®®(e� \ \ 40CIO cl 4 ^00 n. Qk t a a. (otl D•a4 Y� +f • i : I b '• 1 R CV.I�I L /.ItE a•�•� .y ° � 0 � � O SNEAWOOD 3 ° STCatERIDGE ° •i r, ^P ,a U FIRST FILING I 1.0 m m m p STONE Al rl P � � .I .ryNy 1 Q ti I 1 1 / / i 1 VICINITY. L ®ill®oe®' IDGE SECO IUtNG. FINAL DRAINAGE AND EROSION CONTROL STUDY FOR STONE RIDGE P.U.D. SECOND FILING FORT COLLINS, COLORADO March 1, 1993 Prepared for: The Kaplan Company 1060 Sailors Reef Ft Collins, Colorado 80525 Prepared by: RBD, Inc..Engineering Consultants 209 South Meldrum Fort Collins, Colorado 80521 (303) 482-6368 RBD Job No. 503-002 INC. Engineering Consultants 209 S. Meldrum Fort Collins, Colorado 80521 303/482-5922 FAX:303/482-6368 March 1, 1993 Ms. Kate Malers City of Fort Collins Utility Services Stormwater 235 Mathews Fort Collins, Colorado 80522 RE: Final Drainage and Erosion Control Study for Stone Ridge P.U.D. Second Filing Dear Kate: We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion Control Study for Stone Ridge P.U.D. Second Filing. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria We appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. Respectfully, RBD Inc. Engineering Consultants Roger A. Curtiss, P.E. Project Engineer c' Other Offices: Denver 303/458-5526• Vail303/476-6340 TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION 1 A. LOCATION 1 B. DESCRIPTION OF PROPERTY 1 II. DRAINAGE BASINS 1 A. MAJOR BASIN DESCRIPTION 1 III. DRAINAGE DESIGN CRITERIA 1 A. REGULATIONS 1 B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS 2 C. HYDROLOGICAL CRITERIA 2 D. HYDRAULIC CRITERIA 2 E. VARIANCES FROM CRITERIA 2 IV. DRAINAGE FACILITY DESIGN 2 A. GENERAL CONCEPT 2 B. SPECIFIC DETAILS 3 V. EROSION CONTROL 4 A. GENERAL CONCEPT 4 B. SPECIFIC DETAILS 5 VI. CONCLUSIONS 6 6 A. COMPLIANCE WITH STANDARDS B. DRAINAGE CONCEPT 6 C. EROSION CONTROL CONCEPT 6 REFERENCES 7 APPENDIX VICINITY MAP 1 SITE HYDROLOGY 2 DETENTION FACILITIES 8 DESIGN OF CURB INLETS & STORM SEWER 17 DESIGN OF CHANNEL AND SWALES 25 DESIGN OF RIPRAP 33 EROSION CONTROL 35 CHARTS, TABLES AND FIGURES 40 FINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE STONE RIDGE P.U.D. SECOND FILING FORT COLLINS, COLORADO GENERAL LOCATION AND DESCRIPTION A. Location The Stone Ridge P.U.D. development is located immediately northwest of the intersection of Horsetooth Road and County Road 9. The site is bounded on the north by the proposed Pinecone P.U.D. project, on the west by Dakota Ridge, and on the south by Stone Ridge First Filing. The site is shown, along with the First Filing on the Vicinity Map in the appendix. More specifically, the site is situate in the South 1 /2 of the Southeast 1 /4 of Section 29, Township 7 North, Range 68 west of the Sixth P.M., City of Fort Collins, Larimer County, Colorado. B. Description of Property The Stone Ridge P.U.D. Second Filing contains approximately 12.96 acres more or less of which is currently undeveloped and will be developed into single family residential lots. The majority of the property consist of cultivated farmland. Existing topography is generally sloping from the west to the east at approximately 0.5%. II. DRAINAGE BASINS A. Major Basin Description The site is located in the Foothills Basin. The drainage area is specifically described in the report entitled "Foothills Basin (Basin G) Drainage Master Plan" prepared by Resource Consultants, Inc. dated February 1981. III. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. 1 B. Development Criteria Reference and Constraints The Foothills Basin (Basin G) Drainage Master Plan criteria and constraints indicate that the entire Stone Ridge P.U.D. site is to contain a permanent on -site detention facility in the northeast corner of the site. Ultimately the permanent detention pond will be required to release no more than 33 cfs of storm water runoff during a storm event. Temporary storm water detention ponds are to be designed to release up to the 2 year historic runoff rate for the site. Storage volume is to be the difference between the 100 year developed runoff and the 2 year historic runoff. C. Hydrological Criteria The rational method was used to determine runoff peak flows from the site and the surrounding off -site tributary areas. The 2 year and 100 year rainfall criteria, which was obtained from the City of Fort Collins, is the criteria which was utilized. The criteria is included in the Appendix. D. Hydraulic Criteria All calculations within this study have been prepared in accordance with the City of Fort Collins Drainage Criteria. E. Variances from Criteria The grassed swales thought he greenbelts of this project will be graded at approximately 0.6%. A variance is being sought to let the bottom of these remain grass, instead of installing concrete trickle pans. Storm sewers have been designed to accommodate the 2 year storm events for the surrounding basins. IV. DRAINAGE FACILITY DESIGN A. General Concept The Stone Ridge Second Filing is planned as a single family residential housing development. The Second Filing will include 43 single family residential lots. Storm water flows will be generally routed along historic drainage patterns, or from west to east. Included in the back pocket of this report is the Drainage, Erosion Control, and Offsite Grading Plan. 2 B. Specific Details Basin 10 is a small portion of the site in the northwest corner of the site, consisting entirely of green belt, will sheet flow to the north. Basin 11 consists of residential lots and Jadestone Court. Developed runoff from this basin will be directed to Greystone Drive and then south along Greystone to a low point. The minor storm will be collected in a curb inlet and storm sewer, the major storm will overtop the curb and will be directed east and north through the green belt to the northerly property line and routed east to the temporary detention pond. Developed flows from Basins 7 and 8 of the First Filing will also be collected at the low point in Greystone Drive, and routed along with the flows from Basin 11. The storm sewer for the project is intended to convey only the minor, or 2 year runoff through the site. All major, or 100 year flows will be directed to the temporary detention ponds by surface swales and channels. Basin 12 consist of the westerly half of the lots along Greystone Drive. Developed runoff from this basin will also be conveyed to a low point in Greystone, and further conveyed to the detention pond as described above. Developed runoff from Basin 13 and 15 for both the 2 year and 100 year storm events will be directed . to the green belt, towards the northerly property line, and ultimately east to the detention pond. None of the developed flows from these basins is intended to enter the storm sewer. Basin 14 consist of residential lots and Jewelstone Court. Developed runoff will be conveyed to a low point located at the north side of the T intersection. The minor storm will be passed through a metal sidewalk culvert, and then to an open channel between lots 27 and 28. From there open channels will convey flows to the detention pond. Developed flows from basins 7, 8, 11, 12, 13, 14, and 15 are all being routed towards the northerly property line to be routed east to the temporary detention pond. These developed flows will remain separate from any of the developed flows from the Pinecone or Dakota Ridge projects. None of the developed flows from either of those projects (Pinecone P.U.D. or Dakota Ridge)is intended to flow to the on -site detention pond within the Stone Ridge P.U.D. Basins 1-1 and 2-1 coincide with basins 1 and 2 of the First Filing Report. The intent of these basins remains as established in the First Filing. Runoff will be directed towards Fieldstone Drive, and then directed easterly in the KI curb and gutter. At the present time, runoff is collected in a temporary channel and directed north, and then east to the detention pond. The channel section installed with the First Filing will be relocated approximately 200 feet to the east. Developed runoff will still be routed north and then east to the Detention pond. When Fieldstone Drive is developed east of Kingsley Drive, curb inlets will be required to be installed as shown on these plans. A storm pipe will be installed with this filing for those future curb inlets. The owner of the Stone Ridge P.U.D. site does not wish to use the existing pond at the northeast corner of the site for storm water detention at this time. A temporary detention pond was built with the First Filing, and was sized per the FAA method to accommodate developed runoff from the First and Second Filings of Stone Ridge. The detention pond contains a type C area inlet and orifice plate in the pond bottom. The area inlet acts as a sediment collection barrier to help prevent sediment from entering the existing pond at the northeast corner of the site. This inlet will need to be cleaned out on a regular basis to ensure maximum benefit as a sediment collection barrier. The area inlet is temporary with the temporary detention pond and will need to be removed once the permanent detention pond is constructed in the future. With the development of the Second Filing, a new orifice plate will need to be installed in the area inlet. The existing orifice plate has been sized for a release rate of 18.6 cfs; the new orifice plate will contain an orifice sized to allow a release rate of 14.8 cfs. Storm water exiting the temporary detention pond will be transported down the approximate 10% slope by means of a riprap channel and enter the existing pond at the northeast corner of the site. The existing pond has an outlet pipe which discharges into the Fossil Creek reservoir Inlet Ditch. An overflow weir has been installed on the northeast side of the temporary detention pond in the event the outlet pipe becomes plugged with sediment. As future development occurs, the temporary pond will be removed and the existing pond will be used and upgraded to City Stormwater Utility standards. V. EROSION CONTROL A. General Concept The Stone Ridge P.U.D. Second Filing lies within the Moderate Rainfall and Wind Erodibility Zone per the City of Fort Collins zone maps. The potential exists for erosion problems during construction of the Second Filing and after construction until the disturbed ground is revegetated. It is anticipated 4 that the Second Filing improvements will be started in the spring of 1993. Thus the new improvements will be subject to both wind and rainfall erosion. Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites and related calculations in the appendix, the Erosion Control Performance Standard for this project is 75.7%. From the calculations in the appendix, the effectiveness of the proposed erosion control plan is 85.6% during the construction portion of the development. Therefore, the erosion control plan, as specifically detailed below, meets the City of Fort Collins requirements. B. Specific. Details Prior to the start of Overlot Grading, the first step is to insure that the Erosion Control Structures and measures, as installed with the First Filing are in place, and that the existing Temporary Detention Pond will function as a Sediment Trap for the Second Filing. After the Overlot Grading has been completed for the Second Filing, all disturbed areas not in a Roadway or Green belt area shall receive a temporary vegetation seed applied per the City of Fort Collins specifications. After seeding, a hay or straw mulch shall be allied over the seed at a rate of 2 tons/acre minimum, and the mulch shall be adequately anchored, tacked, or crimped into the soil per the City specifications. All new channels and swales shall receive straw bale check dams as soon as possible after overlot grading. Where possible, the existing vegetation and established grass shall be maintained. The pavement structure should be applied as soon as possible after the utilities have been installed. After installation of the curb inlets along Greystone Drive, the inlets shall be filtered with a combination of concrete blocks, 1 /2" wire screen and 3/4" coarse gravel, constructed according to the detail on the detail sheet. After installation of the storm sewer within the green belt area, the green belt shall have a permanent seed mix and mulch applied per the City specifications. 5