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HomeMy WebLinkAboutTIMBERLINE CHURCH P.U.D. - FINAL - 1-97A - SUBMITTAL DOCUMENTS - ROUND 3 - DRAINAGE REPORTVICINITY MAP Z( N =2000 2 VICINITY MAP construction D. Erosion Control Concept The erosion control concepts adequately provide for the control of wind and rainfall erosion from the Timberline Church site. Through the construction of the erosion control concepts, the City of Fort Collins performance standard will be met. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards, by the City of Fort Collins, Colorado, May 1984, revised April 1997. 2. Erosion Control Reference Manual for Construction Sites, by the City of Fort Collins, Colorado, January 11, 1991. 3. Overall Drainage Plan for the Pinecone O.D.P., by Lidstone & Anderson, Inc., March 7, 1995. 6 construction grading can begin. VI. EROSION CONTROL A. General Concept This area is in the Moderate Wind Erodibility Zone and the Moderate Rainfall Erodibility Zone per the City of Fort Collins zone maps. The potential exists for erosion problems during construction and after construction until the disturbed ground is revegetated or paved. B. Specific Details Calculations for erosion control performance standards have been completed per the City of Fort Collins erosion Control Reference Manual for Construction Sites, and have been included with this submittal. The required performance standard during construction was 77.0, and the value for this erosion control design is 90.7. The required performance standard after construction was 90.5, and the value for this erosion control design is 98.0. Based on this the erosion control plan meets the City of Fort Collins Criteria. The total erosion control security deposit is $50,104.00. VII. CONCLUSIONS A. Compliance with Standards All computations completed within this report are in compliance with the Storm Drainage Design Criteria Manual. B. Drainage Concept The combination of swales, and street and storm drain systems will provide for the 10 and 100 year developed flows to reach the proposed on -site detention I facility. The proposed drainage concepts presented in this report and on the construction plans adequately provide for the conveyance and release of developed on -site flows into the downstream conveyance system. If groundwater is encountered at the time of construction, a Colorado Department of Health Construction Dewatering Permit will be required. ' C. Storm Water Quality Concept. ' Because storm water quality has become a requirement, the proposed design has addressed this storm water aspect. Grass lined swales and a detention/retention pond will allow sediment to settle out before entering the downstream conveyance system. In addition silt fence and straw bale check dams will be provided during I5 i Sub -basin 1 is 2.92 acres and represents the building roof area. The run-off from the i roof will be collected at one outfall location on the east side of the building and be conveyed by pipe flow to the ditch on the north side of the pond and from there into the pond. Sub -basin 2 is 3.72 acres and represents a large portion of the east parking area. The runoff from this basin will drain through four sidewalk culverts on the east side of the parking lot and then through overland flow into the detention pond. Sub -basin 3 is 5.34 acres and encompasses the southern half of the main parking lot. It will also drain through four sidewalk culverts on the east end of the parking lot and then into the detention pond. Sub -basin 4 is 3.57 acres and is the soccer field and future building area shown on the east side of the site. This sub -basin will sheet flow into the detention pond. Sub -basin 5 is 6.54 acres and encompasses a portion of a future building and the detention pond. Sub -basin 5 will drain into a ditch which runs along the southern side of the site and then into the detention pond. Sub -basin 6 is 1.57 acres and is a portion of the parking lot for a future building site. This sub -basin drains to the east, through a proposed 10' curb cut and into the detention pond. Sub -basin 7 is 1.86 acres and is a portion of the parking lot for the future building site. This sub -basin combines with sub -basin OS-1 ( 3.47 acres) to drain through three 2' sidewalk culverts and then sheet flow into the Foothills channel. Sub -basin OS-2 represents the southern portion of the CSU site which lies on the west side of the church. This sub -basin will be allowed to sheet flow into the Foothills channel as it currently does. Sub -basins 8 and 9 represent the northern half of the parking lot. These sub -basins will sheet flow to a curb cut on the east end of the parking lot in basin 9 and then be conveyed by Swale to the detention pond. V. STORM WATER QUALITY Because the Timberline Church site sits immediately adjacent to the Foothills Channel the developer has decided to provide a water quality mechanism in the detention pond as well as detention. The proposed water quality measures will require regular maintenance to remove deposits as they accumulate. The storm water quality outlet works will release the first flush of storm water runoff over a period of time in order for the pollutants to settle out of the runoff. All construction activities must comply with the State of Colorado permitting process for Storm water Discharges Associated with Construction Activity. A Colorado Department of Health NPDES Permit will be required before any 0 feet available for detention. In the Pinecone study the site was broken into two sub -basins which were labeled 59 and 60. Sub -basin 59 which was the northern portion of the site was 20.7 acres and sub - basin 60 which was the southern portion of the site was 24.6 acres. According to the Pinecone study sub -basin 60 which also included the property owned by CSU (which lies on the west side of the Church site) and a portion of the apartments which are on the southern side of the Foothills channel, was allowed to release undetained into the Foothills channel. For the updated SWMM the church site has been broken into three sub -basins (59, 60 and 401). Sub -basin 59 is still the north half of the site and encompasses the on -site basins 1,2,3,4,8 and 9. These six basins make up 22.71 acres of the Timberline site. The southern half of the site it still modeled as sub -basin 60 in the revised SWMM. Sub -basin 60 includes on -site basins 5 and 6 for a total area of 8.11 acres. Basins 7, OS-1 and OS-2 are modeled as the new basin 401 in the revised model and encompass 6.98 acres. The remainder of the original basins 59 and 60 which is 7.50 acres has been modeled as a new basin 400 in the revised model. As stated earlier basin 60 in the Pinecone SWMM was allowed to release undetained into the Foothills channel. The total undetained release from sub -basin 60 was set at 88 cfs (see page 14 of the Pinecone Study). Pond 211 in the Pinecone SWMM had a release rate of 9 cfs. Therefore, the total release rate from the two basins was 88 + 9 cfs = 97 cfs, in the Pinecone SWMM. The proposed pond for the Timberline Church will be providing water quality storage within the detention pond as well as detention. Currently, the pond is designed to release 20 cfs between the elevations 4921.2 (water quality pond elevation) and 4923.3. This release rate of 20 cfs is considerably less than what was called for in the Pinecone SWMM. However, sub -basin 401 which includes the CSU off -site basin OS-1 and OS-2 as well as basin 7 from the Timberline Church site are releasing un-detained into the Foothills Channel. This combination of un-detained flows with the detention pond flows matched the existing downstream peaks in the Lidstone Anderson SWMM most closely. B. Specific Details The Timberline Church will be built in two phases. The portion being constructed in Phase I is shown on the phase drawing of the plan set. The entire site will be overlot graded however, and those areas not being constructed during Phase I will be re -seeded. As shown on the Phase drawing a swale will be provided on the south side of the parking lot to direct the runoff from that portion of the site into the detention pond. The pond and outlet structure will be constructed for the full build -out condition. Following is a discussion of the full build out drainage design. The Timberline Church has been broken into 9 on -site sub -basins and 2 off site sub - basins. The two off -site basins OS-1 and OS-2 represent the property owned by CSU which lies to the west of the First Assembly site. i; ' 3 i III. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. lB. • Development Criteria Reference, Constraints and Comparison The drainage criteria used herein is in accordance with the City of Fort Collins Storm Drainage Design Criteria and Construction Standard Manual. On -site detention is being provided with a release rate dictated by The Overall ' Drainage Plan for the Pinecone O.D.P., by Lidstone & Anderson. Copies of pertinent excerpts of this study have been included in the Appendix. ' C. Hydrological Criteria The Rational Method for determining surface runoff was used for the project site. The 10-year and 100-year storm event criteria, obtained from the City of Fort Collins, was used in calculating runoff values. The EPA SWMM was used for I the sizing of the detention pond. These calculations and criteria are included in the Appendix D. Hydraulic Criteria All hydraulic calculations within this report have been prepared in accordance Iwith the City of Fort Collins Storm Drainage Criteria and are included in the Appendix. IE. Variances from Criteria INo variances are being requested. IV. DRAINAGE FACILITY DESIGN A. General Concept ' This site was analyzed as part of the Pinecone O.D.P. A regional detention facility was planned on this site, and is referred to as pond 211 in the Pinecone report. The Pinecone SWMM was used as the base model for this project. IIn the Pinecone study a 2-point rating curve was developed to limit the discharge to 9 cfs from pond 211. The results of the Pinecone study show a volume requirement of 2.3 acre-feet for pond 211. However, this volume requirement was based on an impervious value of no greater than 40% for this site. The actual overall site impervious value is higher than 40%. Because of the difference in I impervious value the site has been graded to include a pond which has 4.23 acre- ' 2 FINAL DRAINAGE AND EROSION CONTROL REPORT FOR THE TIMBERLINE CHURCH PHASE I AND FULL BUILD OUT FORT COLLINS, COLORADO I. GENERAL LOCATION AND DESCRIPTION A. Location The Timberline Church is located east of Timberline Road and north of the new Fort Collins High School, as shown on the vicinity map included in the appendix. The site also sits immediately north of the Foothills channel. More particularly, this site is a portion of the Northwest Quarter of Section 29 Township North, Range 68 West, of the 6" P.M., City of Fort Collins, Larimer County, state of Colorado. B. Description of Property The development contains approximately 32.79 acres, more or less. This area is presently undeveloped, and is currently occupied by native grasses. The site slopes generally from west to east at slightly more than 1%. II. DRAINAGE BASINS AND SUB -BASINS A. Major Basin Description The project site is located within the Foothills Drainage Basin. This site was also addressed as a portion of the "Overall Drainage Plan for the Pinecone O.D.P." by Lidstone & Anderson, Inc., dated March 7 1995. Within the Pinecone report the Timberline Church is specifically referenced as sub -basins 59 and 60. B. Sub -Basin Description Currently runoff from the site is conveyed by sheet flow into the Foothills channel which borders the site on the south. Immediately adjacent to the site there is an existing development which is owned by CSU. The CSU site is on the south west comer of the Timberline Church property. The runoff from the CSU site currently sheet flows across the site and enters into the Foothills channel. Although at the present time Timberline road drains away from the site in a westerly direction, it was included in the drainage sub -basins for this site. In the Ifuture when Timberline Road is widened it will have a 120' right-of-way width. TABLE OF CONTENTS DESCRIPTION I. GENERAL LOCATION AND DESCRIPTION A. LOCATION B. DESCRIPTION OF PROPERTY II. DRAINAGE BASINS AND SUB -BASINS A. MAJOR BASIN DESCRIPTION B. SUB -BASIN DESCRIPTION III. DRAINAGE DESIGN CRITERIA A. REGULATIONS B. DEVELOPMENT CRITERIA REFERENCE, CONSTRAINTS, AND COMPARISON C. HYDROLOGICAL CRITERIA D. HYDRAULIC CRITERIA E. VARIANCES FROM CRITERIA IV. DRAINAGE FACILITY DESIGN A. GENERAL CONCEPT B. SPECIFIC DETAILS V. STORM WATER QUALITY VI. EROSION CONTROL A. GENERAL CONCEPT B. SPECIFIC DETAILS VII. CONCLUSIONS A. COMPLIANCE WITH STANDARDS B. DRAINAGE CONCEPT C. STORM WATER QUALITY CONCEPT D. EROSION CONTROL CONCEPT REFERENCES APPENDIX VICINITY MAP HYDROLOGY CALCULATIONS DETENTION WATER QUALITY DESIGN OF INLETS, STORM DRAINS AND SWALES EROSION CONTROL EXCERPTS FROM PINECONE STUDY BASE 100-YR SWMM MODEL UPDATED 100-YR SWMM MODEL 100 YR S WMM WITH ORIFICE PLUGGED CHARTS, TABLES AND FIGURES PAGE 1 1 1 1 2 r r r r 2 3 0 E 5 5 5 6 6 2 3 9 19 24 44 52 58 86 130 141 THE SEAR -BROWN GROUP FULL -SERVICE DESIGN PROFESSIONALS 209 SOUTH MELDRUM FORT COLLINS, COLORADO 80521-2603 970482-5922 FAX:970-482-6368 August 24, 1999 Mr. Basil Harridan City of Fort Collins Utility Services, Stormwater 235 Matthews Fort Collins, Colorado 80522 RE: Final Drainage and Erosion Control Report for the Timberline Church Phase I and full build out Dear Basil: We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion Control Report for the Timberline Church. 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, The Sear Brown Group Prepared by: A&4- &ze Andrea Faucett Water Resources Engineer Reviewed by: 0QS,`« 4i�.3 Kevin W. Gintry,0,�;. Engineering Manager %s�ciS�� ��� NEW YORK-PENNSYLVANIA COLORADO - UTAH - WYOMING STANDARDS IN EXCELLENCE EQUAL OPPORTUNITY EMPLOYER I I FINAL DRAINAGE AND EROSION CONTROL REPORT FOR THE TIMBERLINE CHURCH PHASE I AND FULL BUILD OUT FORT COLLINS, COLORADO August 24, 1999 Prepared for: Timberline Church Lemay Ave. Ft. Collins, CO Prepared by: The Sear Brown Group 209 South Meldrum Street Fort Collins, Colorado 80521 THE (303)482-5922 SEAR -BROWN GROUP SBG Job No. 786-001 Standards in Excellence r