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Home My WebLink AboutTHE GATES AT WOODRIDGE PUD - FINAL - 55-87C - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT :111 FINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE GATES AT WOODRIDGE FIRST FILING AND THE. OVERLOOK AT WOODRIDGE FIRST FILING INC. Engineering Consultants I F-' it U I FINAL DRAINAGE AND EROSION III CONTROL STUDY FOR THE GATES AT WOODRIDGE FIRST FILING III AND THE OVERLOOK AT WOODRIDGE FIRST FILING U III May 6, 1991 I Prepared for: III Woodcraft Homes 1501 N. Cleveland Ave. 1111 Loveland, Co. 80538 h , Prepared by: ill RBD, Inc. Engineering Consultants 2900 South College Avenue Fort Collins, Colorado 80525 (303) 226-4955 RBD Job No. 434-002 av +p ra u. INC. Engineering Consultants • 2900 South College Avenue Fort Collins,Colorado 80525 303/226-4955 FAX 303/226-4971 141 May 6, 1991 Ms. Susan Hayes City of Fort Collins Utility Services Stormwater 235 Mathews Fort Collins, Co. 80522 RE: Final Drainage and Erosion Control Study for The Gates at Woodridge First Filing and The Overlook at Woodridge First Filing RBD Job. No. 434-002 Dear Susan: We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion Control Study for The Gates at Woodridge First Filing and The Overlook at Woodridge First Filing. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. r .. Thank you for your time and consideration of this submittal. Please call if you have any questions. Respectfully, • O Q° R 0-,,,� RBD Inc. Engineering Consultants 4 0 Gi* w• 7- hi. 24766 LE 1:1.• Kevin W. Gingery, P.E. . `e `' Project Engineer 14. % A� 't�� '�7�l��li/fi11ii1111N1�1� .,. CC: Mr. John Hutchinson - Hutchinson Management Inc. Mr. Gary Berger - WoodCraft Homes �^ A Other offices:Denver 303/778-7338•Vail 303/476-6340•Colorado Springs 719/598-4107•Longmont 303/678-9584 I iiii 4, i � . ,, TABLE OF CONTENTS NIDESCRIPTION PAGE p : I. GENERAL LOCATION AND DESCRIPTION 1 A. LOCATION 1 B. DESCRIPTION OF PROPERTY 1 II. DRAINAGE BASINS AND SUB—BASINS1 A. MAJOR BASIN DESCRIPTION 1 B. SUB—BASIN DESCRIPTION 2 . III. DRAINAGE DESIGN CRITERIA 2 tft A. REGULATIONS 2 B. DEVELOPMENT CRITERIA REFERENCE , , '!'' ' AND CONSTRAINTS 2 C. HYDROLOGIC CRITERIA 3 f° 4• D. HYDRAULIC CRITERIA 3 y , E. VARIANCES FROM CRITERIA 3 IV. DRAINAGE FACILITY DESIGN 3 ,, A, A. GENERAL CONCEPTS 3 B. SPECIFIC DETAILS 3 � ^ V. EROSION CONTROL 5 ��` 5 5 OPT s... A. GENERAL CONCEPTS B. SPECIFIC DETAILS. VI. CONCLUSIONS 6 x `" ^'t A. COMPLIANCE WITH STANDARDS 6 „ ;',,,, „ B. DRAINAGE CONCEPT � `' � C. EROSION CONTROL CONCEPT 8 �s REFERENCES ,i�, r`n4R APPENDIX ' 1 �� 1,IIII ' ,mi � VICINITY MAP ,,:" .FIRST FILING HYDROLOGY 2 d'� - ' we `N 6 a {ak\5" ,'M 4 " ,� � `fENTTON i, 8 : �j 7 ,, :DESIGN OF INLETS, STORM SEWER AND SWALES �l 13 l" - F , ,,, �,''� 4 ZPRAP DESIGN �; 15 � = , SION CONTROL . � k ITS, TABLES AND FIGURES 20 f � Vr +vrt P FINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE GATES AT WOODRIDGE FIRST FILING J AND THE OVERLOOK AT WOODRIDGE FIRST FILING I. GENERAL LOCATION AND DESCRIPTION II! A. Location The Gates and The Overlook at Woodridge P.U.D. 's are located east of Taft Hill Road (County Road 19) and north of the existing Harmony Road. The development is bounded by Webber Junior High School and Regency Park PUD to the east and open space (proposed future filings) and 111 Imperial Estates to the north. The site location can also be described as situated in the Southwest 1/4 of Section 34, Township 7 North, Range 69 West of the 6th P.M. , City of Fort Collins, Larimer County, Colorado. 111 The site location can be seen on the Vicinity Map in the Appendix. B. Description of Property The First Filing of The Gates and The First Filing of The Overlook at Woodridge together contain 17.2 acres more or less. Presently, the property is undeveloped. The property is being proposed for planned unit development within the City of Fort Collins Zoning District PUD. 01 Native Colorado grasses cover the property presently. The topography of the site generally slopes from the west to the east at approximately. 1. 3 percent. II. DRAINAGE. BASINS AND SUB-BASINS 0! A. Major Basin Characteristics 0! J. The proposed developments lie within P p p Basins 75 and 80 of the McClellands and Mail Creek Major Drainageway Plan prepared by Cornell Consulting Company. A natural , ;. drainageway runs west to east along the northern edge of The Gates at Woodridge First. Filing boundary within Basin 80. Runoff from Basin 80 is routed by open channels and culverts along the north side of Seneca Street past Webber Junior High School and then along the east side of Regency Drive to the existing Regional Detention Pond. The Overlook at Woodridge development lies in both Basins 75 and 80. Runoff from Basin 75 is routed through the Regency Park development (east of the 1 `akk: Ale Woodridge property) in an open channel along the north Iside of Harmony Road and eventually into the existing Regional Detention Pond. B. Sub-Basin Description The project site has been divided into eight (8) sub- basins of which three (3) were assumed to be developed and the other five (5) were off-site undeveloped. The three (3) developed sub-basins incorporated the proposed building lots and most of the street improvements. The 1111 five (5) undeveloped sub-basins consisted of natural ground cover and portions of the proposed street improvements. These sub-basins are shown on the Drainage and Erosion Control Plan in the back pocket of this report. III. DRAINAGE_ DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. No deviations from the criteria is being sought for the proposed subdivision sites. B. Development Criteria Reference and Constraints From The Final Drainage Report for Regency Park P.U.D. , 100 year developed runoff from Basin 75 will be routed through the Regency Park subdivision in an open channel along the north side of Harmony Road. A 42 inch culvert lies under Regency Drive,, but the outlet invert is a couple of feet lower than the surrounding ground. With enough flow in the pipe, the water would continue to flow to the east toward the Regional Detention Pond. From the Preliminary Drainage Report for the 1990 Junior High School, the channel and culvert system along the north side of Seneca Street and the east side of Regency Drive was sized for undetained on-site as well as undetained off-site 100 year developed runoff from Basins 79,80, and 85. A current SW model analysis for Basins 79,80, as recently obtained by the City of Fort Collins, has determined that the existing channel, culverts and Seneca Street (downstream of the subject site) will receive greater 100 year developed runoff than was originally anticipated. The City of Fort Collins is f — currently reviewing this matter. 2 AP 4 ' C. Hydrologic .Criteria tg, The Rational. Method for determining surface runoff was r"` used for the project site. The 2 and 100 year storm *{"; = event criteria, obtained by the City of Fort Collins, was utilized in calculating runoff values. These calculations and criteria are included in the Appendix. D. Hydraulic criteria ,14t All hydraulic calculations within this report have been 0 "` ' prepared in accordance with the City of Fort Collins Drainage Criteria and are also included in the Appendix. _f. E. Variances from Criteria III No variances are being sought for the proposed project "0 site. A, rt III IV. DRAINAGE FACILITY DESIGN � N A. General Concept III All on-site runoff produced by the proposed development iiiij of The Gates and The Overlook - First Filings will flow easterly to the existing natural drainageways and __ eventually arrive at the Regional Detention Pond. Included in the back pocket of this report are the proposed drainage and grading plans. B. Specific Details The 2 year and 100 year storm runoff produced from sub- basins 2 and 3 in The Overlook development and adjacent off-site sub-basins (0-4 & 0-5) are conveyed within Overlook Drive. At the intersection of Overlook Drive and the realigned Harmony Road, this runoff splits north F; and southeast. Developed runoff from sub-basins 3 and 0- -b bV 5 is directed north into a temporary swale (Swale D-D) III which runs within the proposed Harmony Road right-of-way to the natural drainageway swale along the northern edge of The Gates development boundary. Developed runoff from sub-basins 2 and 0-4 is directed southeast along realigned Harmony Road and into an existing roadside ditch next to existing Harmony Road. " The developed runoff that is conveyed by the realigned - Harmony Road and the runoff from the off-site sub-basin 'y 0-3 is collected in the existing roadside ditch that runs IIIIalong the north edge of Harmony Road. A 21 inch RCP ( culvert will be placed under the temporary entrance road IC into the developments to convey these flows toward the ill3 I Regional Detention Pond to the east. The 2 year and 100 year storm runoff produced from sub- basin 1 in The Gates development and adjacent sub-basin 0-1 is conveyed in Seneca Street in a northeasterly direction. Two proposed 10 foot Type "R" curb inlets are located at the eastern boundary of the subject site where the proposed Seneca Street extension ties into the existing Seneca Street. One inlet is proposed on each side of the street. The inlets will collect a portion of the 2 year storm runoff and redirect the runoff away from the street. Inlet #2 (south side) will collect 1.8 cfs and pass 0. 6 cfs east on Seneca Street. Inlet #1 (north -- side) will collect 5. 1 cfs and pass 4.2 cfs east on Seneca Street. A 15 inch diameter reinforced concrete pipe (RCP) will then take the collected runoff from the inlets and outlet the runoff upstream of two existing 42 inch diameter culverts which lead into a low area just south of Webber Junior High School. I _. Storm water runoff through the existing 42 inch culverts travels east via other culverts and open channels, and eventually reach the Regional Detention Pond. The City of Fort Collins is currently studying the possible realignment of these two existing 42 inch culverts to provide a more efficient transmission of storm water to the east. For the subject developments, the developed runoff is proposed to b.e directed to the existing 42 inch culverts by the above described storm sewer system and temporary swales (Swales A-A and C-C) . The existing 42 inch culverts have a combined capacity of approximately 114 cfs. For this development, swales A-A and C-C have ® been sized to carry the historic 100 year flow of 52.4 �9 cfs at the 42 inch culverts. The 52.4 cfs capacity exceeds the developed onsite runoff which will pass Mii before the historic runoff peak is realized. As the City of Fort Collins completes their study of these existing 42 inch culverts, their realignment and future use in the main drainageway of this development will be incorporated 011 with future filings of the Woodridge development. A temporary swale (Swale B-B) which runs northeast within the proposed right-of-way of Overlook Drive will collect nuisance runoff and 2 and 100 year runoff generated by the off-site sub-basin 0-2. The swale will join into the natural drainageway swale which runs along the northern edge of The Gates at Woodridge First Filing boundary. 4 II I V. EROSION CONTROL I,' A. General Concepts Both developments, The Gates and The Overlook First 0 Filings, lie within the High Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone per the City of Fort Collins' zone maps. The potential exists for moderate erosion problems after completing the First I' Filing improvements, due to the existing and proposed site slopes of 2. 0 % more or less. It is also anticipated that project site improvements will be I' constructed during the summer of 1991. Thus, the new improvements will be subject to both wind and rainfall erosion before new vegetation can take hold or before the Inew residential lots are developed. The Erosion Control Performance Standard (PS) for both II sites was computed to be 79. 1% per the criteria in the City of Fort Collins Erosion Control Reference Manual for Construction Sites. The Effectiveness (EFF) of the proposed erosion control plan was calculated to be 80.7%. I Therefore, the erosion control plan as. detailed below meets the City of Fort Collins' requirements. llB. Specific Details Sub-basins 0-1 through 0-5 consist mainly of native II! vegetation and grasses. These areas are presently open areas with future plans to be later developed. At this time, however, the existing ground cover should be maintained in these areas. Where temporary swales are to 111 be graded in these areas, erosion hay bale check dams are to be installed at intervals of 500'±. 111 Sub-basin 1 incorporates The Gates at Woodridge First Filing of 29 residential lots and a portion of Seneca Street. Once Seneca Street has been rough cut in and prior to construction of the pavement, straw bale erosion II barriers should be installed on alternating sides of the street. The bales should be perpendicular to the sides extending to the road centerline at 150' intervals. II! After the installation of the pavement, curbs and gutters, and curb inlets, gravel filters should be installed around each 10 foot type R inlet. These gravel Iii filters should consist of a combination of concrete cinder blocks, 1/2" wire mesh, and coarse gravel (3/4/1 diameter) . These filters should also be cleaned or PIreplaced .often.After overlot grading has been completed in sub-basin 1, P5 Ai all disturbed areas should be roughened and seeded with I a temporary seed mix to reduce rainfall erosion. To reduce the wind erosion in this sub-basin, a perimeter barrier such as a silt fence or a row of straw bales should be placed in a northeast to southwesterly IIIdirection. Sub-basin 2 incorporates The Overlook at Woodridge First Filing of 11 residential lots and a portion of Overlook Pi Drive Street. Once Overlook Drive has been rough cut in and prior to construction of the pavement, straw bale erosion barriers should be installed on alternating sides III of the street. The bales should be perpendicular to the sides extending to the road centerline at 150' intervals. After overlot grading has been completed, all disturbed III areas should be roughened and seeded with a temporary seed mix to reduce rainfall erosion. In addition, a hay or straw mulch should be applied over the seed mixture at a rate of_ 2 tons/acre and should be adequately anchored., tacked, or crimped into the soil. Ili ., Sub-basin 3 incorporates The Overlook at Woodridge First III Filing of 15 residential lots and a portion of Overlook Drive Street. Once Overlook Drive has been rough cut in and prior to construction of the pavement, straw bale II erosion barriers should be installed on alternating sides of the street. The bales should be perpendicular to the sides extending to the road centerline at 150' intervals. After overlot grading has been completed, all disturbed ® areas should be roughened and seeded with a temporary `I seed mix to reduce rainfall erosion. VI. CONCLUSIONS PI A. Compliance with Standards All computations that have been completed within this 10! report are in compliance with the City of Fort Collins' Erosion Control Reference Manual for Construction Sites and Storm Drainage Design Criteria Manual. In addition, �1 all computations are in compliance with the Master Drainage Study for Arapahoe Farms prepared by RBD in April 1991. 10! B. Drainage Concepts The proposed drainage concepts adequately provide the transmission of developed on-site runoff to the existing drainage devices at the eastern property line of the II! subject site. The proposed storm sewer system will adequately reduce the 2 year runoff leaving the site along Seneca Street. II! 6 III C e III The City of Fort Collins is currently studying the III realignment of the existing 42 inch culverts at Webber Junior High School adjacent to Seneca Street. Depending on the outcome of this analysis, the existing 42 inch culverts may or may not be relocated. For this II development, we have designed temporary swales that deliver developed runoff from The Gates at Woodridge First Filing and The Overlook at Woodridge First Filing III to the existing 42 inch culverts along the east property line. The 15 inch storm sewer has been designed with an outlet elevation that can accommodate a relocation of the existing 42 inch culverts to the north. Final grading of III the main drainageway through the Woodridge development is not being proposed at this time due to the current study underway with the existing 42 inch culverts along the U east property line. In addition to the 42 inch culvert study, the City of III Fort Collins is also evaluating the capacity of downstream existing improvements in regards to the new SWMM runoff flows which exceed the previously used downstream criteria. For the subject developments, III adequate downstream capacity in the culverts, open channels, and street systems exists to safely convey developed runoff to the existing Regional Detention Pond. III Developed runoff from The Overlook at Woodridge First Filing is proposed to be transported in the existing roadside ditch along the north side of Harmony Road to U the east towards the City of Fort Collins Regional Detention Pond. A 42 inch culvert carries the flows . under Regency Drive, but the outlet invert is a couple of U feet lower than the surrounding ground. With enough flows in the pipe, the water would continue to flow to the east, toward the Regional Detention Pond. With theIII development of the property at the northwest corner of Regency Drive and Harmony Road, the outlet of the existing 42 inch culvert under Regency Drive will be improved to enable storm water runoff to efficiently II. reach the Regional Detention Pond. It is our understanding that this corner property may be developed in the near future and therefore no improvements are proposed by this development, to the existing 42 inch culvert situation at Regency Drive and Harmony Road. When development occurs in the future on the southeast corner of the Woodridge development adjacent to sub-basin 0-1, a temporary detention pond may be required within this development. The temporary detention pond may be MI required if the downstream improvements to the outlet of the existing 42 inch culvert under Regency Drive have not been completed to enable storm water runoff to II! 7 ILI III ' _ efficiently reach the Regional Detention Pond. !IIC. Erosion Control Concepts The proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from The III Gates at Woodridge First Filing and The Overlook at Woodridge First Filing. Through the construction of the l proposed erosion control concepts, the City of Fort IIICollins 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 IIIthe City of Fort Collins erosion control criteria. IIIREFERENCES 1. Storm Drainage Design Criteria and Construction Standards by III the City of Fort Collins, Colorado, May 1984. 2. Erosion Control Reference Manual for Construction sites by the City of Fort Collins, Colorado, January 1991. III 773 3. Master Drainage Study for Arapahoe Farm by RBD, Inc. , Engineering consultants, April 3, 1991. III 4. The McClellands and Mail Creek Major Drainageway Plan by Cornell Consulting company, December 1980. 5. The Final Drainage Report for Regency Park P.U.D. by Parsons and Associates Consulting Engineers, March 30, 1987 . 6. Preliminary Drainage Report for the 1990 Junior. High School by I RBD, Inc. , February 5, 1988. 7. Final Drainage Report for Poudre School District R-1 III Elementary School by Engineering Professionals, Inc. , April 1987. III 041, , ' - II II! /