The URL can be used to link to this page

Home My WebLink AboutARAPAHOE FARM TOWNHOMES PUD - PRELIMINARY - 55-87G - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT PRELIMINARY DRAINAGE AND EROSION CONTROL STUDY FOR ARAPAHOE FARM FORT COLLINS, COLORADO 91EIINC. Engineering Consultants PRELIMINARY DRAINAGE AND 1111 EROSION CONTROL STUDY FOR ARAPAHOE FARM 14 FORT COLLINS, COLORADO October 25, 1993 U U Prepared for: Client: James Company 2919 Valmont Road, Suite 109 Boulder, Colorado 80301 U Prepared by: RBD, Inc. Engineering Consultants U 209 South Meldrum Fort Collins, Colorado 80521 (303) 482-5922 RBD Job No. 607-001 U ■ ■ 3DINC. Engineering Consultants 209 S.Moldrum Fort Collins,Colorado 80521 e 303/482-5922 FAX:303/482-6368 ■ U October 25, 1991 Ms. Kate Malers City of Fort Collins Utility Services Stormwater 235 Mathews Fort Collins, Colorado 80522 RE: Preliminary Drainage and Erosion Control Study for Arapahoe Farm Dear Kate: We are pleased to submit to you, for your review and approval, this Preliminary Drainage and Erosion Control Study for Arapahoe Farm. 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 1111 Terry P. McEnany :, a. °�• Gi4,%.<(), .y.t.tiy,;„\.., W..11-(;4- 5-- Kevin W. Gingery, .E. J. .• n► t}t 1111 Jnllu Other Offices: Denver 303/458-5526•Vail 303/476-6340 TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION A. LOCATION 1 B. DESCRIPTION OF PROPERTY 1 II. DRAINAGE BASINS A. MAJOR BASIN DESCRIPTION 1 B. SUB-BASIN DESCRIPTION 2 III. DRAINAGE DESIGN CRITERIA A. REGULATIONS 2 B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS 2 C. HYDROLOGICAL CRITERIA 2 D. HYDRAULIC CRITERIA 2 E. VARIANCES FROM CRITERIA 3 IV. DRAINAGE FACILITY DESIGN A. GENERAL CONCEPT 3 B. SPECIFIC DETAILS 3 IN V. STORM WATER QUALITY A. GENERAL CONCEPT 4 B. SPECIFIC DETAILS 4 VI. EROSION CONTROL 1.1.1111 A. GENERAL CONCEPT 4 VII. CONCLUSIONS 71111 A. COMPLIANCE WITH STANDARDS 5 B. DRAINAGE CONCEPT 5 C. STORM WATER QUALITY 5 El D. EROSION CONTROL CONCEPT 5 REFERENCES 6 II APPENDIX A MI VICINITY MAP Al HYDROLOGY A2 DETENTION A8 IIII DESIGN OF INLETS, STORM SEWERS AND SWALES A16 111 MI ■_ PRELIMINARY DRAINAGE AND EROSION CONTROL STUDY ■ FOR ARAPAHOE FARM FORT COLLINS, COLORADO lig I. GENERAL LOCATION AND DESCRIPTION A. Location The Arapahoe Farm development is located north of Harmony Road and immediately southeast of Seneca Street. The site is shown on a Vicinity Map in the appendix. The site is located immediately east of the Gates at Woodridge P.U.D.. More particularly, the proposed development is located in the Southwest Quarter of Section 34, Township 7 North, Range 69 West of the Sixth P.M., Larimer County, Colorado. B. Description of Property The Arapahoe Farm development contains approximately ten acres of area that is currently undeveloped and being proposed for residential development. The property has consisted of rangeland, but is currently surrounded on nearly all sides by developed land. The property is bounded on the northwest by Seneca Street, and on the south be Harmony Road. The Regency Park development borders to-the east. The site generally slopes downward from west to east at approximately 1.5 percent grade. No information regarding soils type of groundwater information is known at this time, but should be investigated prior to final design. II. DRAINAGE BASINS A. Major Basin Description The site is located in the McClellands and Mail Creek Basin. This drainage 111 area is specifically described in the report entitled PRELIMINARY/MASTER DRAINAGE STUDY FOR WOODRIDGE, prepared by RBD Inc. 1991. 1111 U 11111 B. Sub-Basin Description Historical drainage patterns for the site are northeasterly and southeasterly toward the McClellands and Mail Creek Drainageway. The previous study by RBD, Inc. identifies developed drainage sub-basins 7A, 7B, 7C, 16 and 17 as contributing to drainage onto and across the site. This preliminary report incorporates the analysis for off-site sub-basins 7A, 7B, and 7C from the Woodridge Master Plan into the plan for Arapahoe Farm. 11111 III. DRAINAGE DESIGN CRITERIA 1111 A. Regulations All regulations as established by the City of Fort Collins Stormwater Utility will be used for this preliminary drainage study. 14 B. Development Criteria Reference and Constraints The Preliminary/Master Drainage Plan for Woodridge criteria and constraints are being utilized in this preliminary drainage study. Drainage criteria not ' specified in the Woodridge study will be in accordance with the City of Fort Collins Storm Drainage Design Criteria and Construction Manual. On-site detention is not required for sub-basin 1, but off-site constraints require detention of flows at Design Point 2. The Woodridge study points out that the channel running east along the north side of Harmony Road through the Regency Park development has a design capacity of 42 cfs, therefore the flows entering this channel from Arapahoe Farm must be equal to 42 cfs, or the channel must be improved. This design incorporates on-site detention using a staged release rate of 42 cfs for a 100 year design storm. C. Hydrological Criteria The rational method was used to determine runoff peak flows from the site. The 2 and 100 year rainfall criteria, which was obtained from the City of Fort Collins, is the criteria which was utilized for this study. This 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 Storm Drainage Criteria. 2 1111 E. Variances from Criteria 1111 No requests are being made at this time for variances from the standard criteria. IV. DRAINAGE FACILITY DESIGN A. General Concept As development occurs within the Arapahoe Farm site, the drainage concepts shown on the Preliminary Drainage and Erosion Control Plan, in the back pocket of this report, should be followed. The two detention ponds are included in the plan for hydraulic design and water quality criteria. B. Specific Details A soils report for the Arapahoe Farm development was not available at this time. If groundwater is encountered during construction, a Colorado Department of Health Construction Dewatering Permit will be required. The site has adequate elevation relief to provide for surface drainage. 111 Flows will be diverted to interior drives with reverse crown sections. Rain falling in Seneca Street will flow in street curb and gutter and drive cross pans toward the existing 10' type R curb inlet at the northeast corner of the site. Horizontal site constraints prompted the design of a storm sewer to convey off-site flows east within the future north Harmony Road Right-of-Way to outfall into Detention Pond #2 when Harmony Road is realigned. The existing Harmony Road alignment joins the new Harmony Road by a temporary access drive. Offsite flows currently run in a roadside swale along the north side of Harmony Road, crossing the access drive in a temporary culvert as it travels east to be carried in an existing drainage swale along the south side of Regency Park. The Drainage Plan calls for the proposed storm sewer to carry all the flows in the roadside swale as well as 4.4 cfs diverted into the sewer by a proposed 20' type R curb inlet at the south corner of Seneca Street and Harmony Road. Flows in the north Harmony Road curb and gutter are to be collected by a 16' type R curb inlet located near the southeast corner of the site. A 15" pipe will convey those flows to Detention Pond #2. 3 • 111111 V. STORM WATER QUALITY A. GENERAL CONCEPT Beginning in October of 1992, the water quality of storm water runoff was required to be addressed on all final design utility plans. The Arapahoe Farm development is anticipating construction beginning in 1994. Therefore, for this study, we have sought to find various Best Management Practices for the treatment of storm water runoff at this preliminary design phase which could be implemented in the final design process. B. SPECIFIC DETAILS IN It is our understanding at this preliminary phase, that the concept of storm water quality should address the treatment of the initial first flush runoff in a water quality pond, so the pollutants can be filtered out of the storm water runoff. The two detention ponds will collect nearly all of the runoff from the _ site. Trickle pans will not be constructed so that runoff can filter through the grass. Suspended particles will be allowed to settle in the ponds during the higher flow events. Aeration of turbulent flow over riprap at the inflow points of the ponds will also provide for improved water quality. VI. EROSION CONTROL UA. General Concept The Arapahoe Farm development lies within the Moderate Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone according to the City of Fort Collins zone maps. The City of Fort Collins Erosion Control Reference Manual for Construction Sites specifies that, at the time of final design of the site, the erosion control performance standard will need to be calculated — and appropriate measures taken to control erosion from the site. Conceptual erosion control features are shown on the Preliminary Drainage 11111 and Erosion Control Plan. They include gravel filters, riprap protection, and straw bale dikes. All construction activities must also comply with the State of Colorado permitting process for Stormwater Discharges Associated with Construction Activity. A Colorado Department of Health NPDES Permit will be required 11111 before any construction grading can begin. U 4 • U VII. CONCLUSIONS A. Compliance with Standards All computations within this report have been completed in compliance with 1111 the City of Fort Collins Storm Drainage Design Criteria.a. B. Drainage Concept The proposed drainage concepts adequately provide for detention of developed runoff from the Arapahoe Farm site. The preliminary size of the detention ponds will enable the site to develop in conformance with the Preliminary/Master Drainage Plan for Woodridge. The detention ponds should be provided with one foot of freeboard and an emergency overflow outlet in the event an outlet becomes plugged. IN If groundwater is encountered during the construction of any portion of the site and dewatering is used to install utilities, then a State of Colorado construction Dewatering Wastewater Discharge Permit will be required in 1111 order for this water to be discharged into any waters of the United States. C. Storm Water Quality INBecause storm water quality has become a requirement, the site will need to address this storm water aspect. The detention ponds proposed in this report have several features that increase water quality leaving the site. Natural processes of aeration, filtration, and settling provide for cleaner water. The detention ponds will require regular maintenance to remove 111 deposits as they accumulate. D. Erosion Control Concept Appropriate erosion control measures and calculations of the overall performance standard will be done for the final design of the site according 1111 to the City of Fort Collins Erosion Control Reference Manual for Construction Sites. 1111 11 U REFERENCES 1. Storm Drainage Design Criteria and Construction Standards, by the City of Fort Collins, Colorado, May 1984, revised March 1991. 2. Erosion Control Reference Manual for Construction Sites, by the City of Fort Collins, Colorado, January, 1991. 3. Preliminary/Master Drainage Study for Woodridge, by RBD, Inc., December 1991. U IN U U U 6 • . . . . .. . ,.. . • • II • • ettl. . . . , . • . • • . • . . . .. • . . . .. . .. . . . . . N . .. .. • .• • • . . . . . — .• . .. • • • III] • . ai i • , t=1.,Z: ti..7 ,-- ,L, p . 141,,,,,,,,... 6 • . I .I.Lt_EL.44 WW1; ' II MIR MI OM NM .3. ill - II. Oil 1•11.1 aiuti , MIN 11 I • ,i. W,,, liorsetoot .Road rAmt.111..Cl 'agailiall aal Nig Ear. Ma n 40; 1 i, I Arbor,...0 ...., .., 0,0 7 i •,,,t. e .F fi ,-) Brook Orr.. .... t j % •i:Ranh° Ago 0 : A A. 1 IIII CC u t MU MI NM NW NMI NW - .." ' Wolfd ., —.. • -- '' o ori (1..... . i I -- ...) i 8 "..,„‘ i CI 1 .. .14 25 17 n. i .-• wher..4 or --!' "i 4 1 I (1) I-- .•-e c Lir 10P' .= Basle. 14 1 is II '----\•• (f) C: \i. -0 %_ • li, INV ,t r• .C• • l‘MINI NMI NMI MINI NM i SPfi., C,••1 0." -, D•me I (..% '••C 6 .i.; ' '51 - - 1. C.....17 1......1 Mk 5Io• • I ..,'• U) R'WO VIIIIIP Rd , a4 w..i _ ' ,„•‘• to . rt.: r..1 I cilL",'° AI' •,S1. q ... Air 9 V i ci 0 • tl• . ..st ,. Ltb° co ...,,,, .., 1 , ... 1. 15., or. 2 I 11 /11111 ma 4 imi ma iiki ...0 armony Roos" a I II PROJECT SITE ei .....s1.41 11 No...Mr () 1 II I 44.• oral I 'r a 4:Cr. I Nr 9 IO • k 1 • .... 1 , „ ,..... III 1 ,_ —\__. r- ',..__....- ,..1 L"\ /1-•—e. . 1 IIIAIIMM NM MO MI Milril MMIMMIN MEN VON —NM VW OM MAN MR NW VW MK NM 0 •••• St r••••c D.;:`":".4. 1 , III ..., . ., . e,. • m;d.....y D. 1 1111 1 III 1 III VICINITY MAP . SCALE: 1" = 2000' , 1 Eli