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Home My WebLink AboutDrainage Reports - 01/23/1990STEWART&kSSOCIATES Consulting Engineers and Surveyors. January 17, 1990 Ms. Susan Hayes Storm Drainage Utility City of Fort Collins P 0 Box 580 Fort Collins, CO 80522 RE: DRAINAGE FOR REPLAT OF LOT 9 AND TRACT "B", BLOCK 4, BROWN FARM SIXTH FILING Dear Susan: The following is a letter regarding Storm Drainage for the. proposed Replat of Lot 9 and Tract "B", Block 4, Brown Farm Sixth Filing. The site is located at the southeast corner of Yorkshire Street and Clydesdale Drive. There is an existing single family residence on Lot 9. Tract "B" is undeveloped ground. The total site area is 81,051 square feet. The original design for Tract "B" was for a recreational center with pool and tennis courts. Drainage and detention requirements for Tract "B" and Lot 9 were included in the overall plan for the Brown Farm Sixth Filing. All runoff from the site goes to the existing detention pond situate on Tract "A" of the said Sixth Filing by way of the existing drainage channel along the south property line. It is our proposal to replat Tract "B" into 5 single family lots. Lot 9 has been included in this project to revise the west property line only. See Sheet 1 of 2 of the Utility and Drainage Plans included with this letter for lot locations and drainage patterns. There will not be any increase in runoff from the original use to this proposed use; therefore, no revisions are needed for the existing detention pond or the existing drainage channel. The original drainage report used a C value of 0.5 for the proposed recreational center. For single family residences we would also use a C value of 0.5 which would give us the same results as the original calculations. We have included parts of the original report for your review. Our project is in their Sub —basin E. The C value is shown on page 12 of 36. Part of Lots 1, 2, 3 and 4 will drain to Clydesdale Drive. Lots 5 and 6 and the balance of Lots 1, 2, 3 and 4 will drain to the existing drain channel along the south boundary line. If you have any questions or if I can be of any further assistance regarding this project, please let me know. Sincerely, Fran 1,in D. Blake, P.E. & L.S. Secretary/Treasurer lkk James H. Stewart enclosure and Associates, Inc. 214 N. Howes Street P.O. Box 429 Ft. Collins, CO80522 303/482-9331 ,7839 OF FINAL DRAINAGE REPORT for BROWN FARM, 6th and 7th FILING 0 CITY OF FORT COLLINS June 1, 1979 Revised July 16, 1979 i. PROJECT LOCATION AND DESCRIPTION This study was performed on Brown Farm 6th and 7th filing in the City of Fort Collins. Its location is shown on the Inset of a portion of a U.S.G.S. map shown on the Master Drainage Plan (Sheet 1), Included in the back of this report. The site is located in one historic drainage basin which drains to the Pleasant Valley and Lake Canal. The proposed subdivision plan calls for the 89.23-acre project to be subdivided Into 298 single-family lots and a recreation center. Average lot size will be approximately 8,000 square feet upon which single—family detached units of approximately 1,200'square feet are proposed to be built. II. DESIGN CRITERIA AND REQUIREMENTS The estimated peak 100-year runoff rates have been calculated based upon the assumed development and runoff pattern. This report is intended to meet the City of Fort Collins drainage design criteria as well as the criteria of the Department of Housing and Urban Development - Federal Housing Administration as set forth In their directive, "Land Planning Guidelines for HUD/FHA Projects." III. METHOD OF ANALYSIS Peak runoff rates were calculated based upon the rational method. The City of Fort Collins Rainfall Intensity - Duration Curve was used for determining intensities. The Master Drainage Plan presented in the back of this report identifies drainage sub -basins and indicates the contributing basin area as well as the peak 100-year runoff rate estimated at the point of concentration as indicated. All calculations are included in the letter part of this report. IV. OFFSITE DRAINAGE -CONTRIBUTION All contributory offsite drainage comes from west of the site. Most of Sub -basin C 'is.offsite and a small portion of Sub -basins B and D are offsite. Offsite drainage is included in all calculations of peak runoff rates. Offsite drainage-iC no* InzWed in the calculations for_,s.i.zLng the detention pond. Only that runoff which is generated from the site is considered in the detention calculations. :::� bNJer�IOW rouii146 iwlr� V. SITE DRAINAGE A. Sub -basins A` and L Due to the lot grading required in these two areas for adequate drainage, a small amount of runoff will drain to Drake Road. It will then be picked up by the proposed gutter along the North side of Drake Road and flow East. i B. Sub -basins B, C, D, and E A sag point in Yorkshire Street will pick up flow coming in from the North and.South. Sub -basins B, C, and D all drain to this sag point. ,The channel in Basin C is passed under Yorkshire Street at this point in a 36-inch 0 R.C.P. culvert. Sub -basins B and D drain to curb inlets at this sag point in Yorkshire. These curb inlets drain into a 27-inch 0 R.C.P. culvert which crosses the street. Excess flow, which these inlets cannot accommodate, will flow East on Montmorency Street. Both of these culverts empty into the box at the curb inlet on the'East side of Yorkshire. A 60-inch x 38-inch`R :Oval invert comes out of the East side of the box and-empties--into"the 18-foot wide grass -lined channel. This channel -2- E u flows East through Sub -basin E and drains into the detention pond. The channel accommodates all the runoff from Sub -basins B, C, D, and E. C. Sub -basin F Sub -basin F will drain along Clydesdale Drive to the sag point in Clydesdale and then into the detention pond via curb inlets and a G24*inch 0 R.C.P. culvert. D. Sub -basins G, H, I, J, and K Sub -basins G, H, and I will drain East to Montmorency Street and then North along Montmorency to the sag point at the detention pond. Some of the runoff from Sub -basin G will overflow the centerline of Montmorency at the intersection with Blue Grass Drive. This excess will flow North to Quince Court and then East to the low point at the end.of-Quince. Sub - basin J will drain North on Yorkshire Street to Montmorency. Sub -basins J and K will drain East on Montmorency to the sag point at the detention pond. At this point the runoff from Sub -basins G, H, I, J, and K will empty into the detention pond via.curb inlets an a 33-inch R,C T! culvert. E. Sub -basins M, N, and 0 Sub -basin M drains to a curb inlet at the low point at the end of Lodi Court. From this point the water is carried by a 15-inch 0 R.C.P. culvert to the 14-foot wide grass -lined channel along the East property line. Sub -basin N drains to a curb inlet at the low point at the end of Quince Court where it is picked up by a similar 15-inch culvert which empties into the same channel. This channel accommodates all of the run- off from Sub -basins M, N, and 0. It drains North to a 36-inch 0 R.C.P. - 3- culvert which passes the water under Wyandotte Drive and into the detention pond. F. Sub -basins P and Q Sub -basin P drains East on Stuart Street to an existing catch basin. Sub -basin Q drains North on White Rock Court and then Southeast to an existing'catch basIn•in Langshire Drive in the 5th Filing of Brown Farm. VI. DETENTION The detention pond is sized to accommodate the runoff from a 100- :year storm while releasing the historic runoff from a 2-year storm. This requires a pond size or 9.73 acre-feet, ith an area of 3.05 acres --and an average depth-�of"3.19 feet._""The release structure is a 21-inch 0 R.C.P. culvert which releases 19.3 CFS. ' VII. SUMMATION The proposed Brown Farm 6th and 7th filing has been designed to accommodate an initial storm with a return period.of two years and a major storm with a return period of 100-years. Runoff will be conveyed in street curb and gutter sections, channels, and storm drains. it is anti- cipated that no damage to proposed structures will occur within this rsubdivision in a 100-year flood and that no damage to upstream or down- stream properties will occur. -4- u DO NOT WRITE IN THIS SPACE eE.v / s 'fF.D 7- 7779 Work Description W.O. No. Date By Sheet / Z of i.. '90 i _.... _ 1=.E/�.:i�. _ fiIYPRAvL-ic....CygRTS..N:F.'c, 2 0 I _ .2 g : : I r i o T ' ,¢S7A% • _1�;.-, -,- . YjB S /.J1j-S _ _ _ 8 t_ C -t_ �. � ,E) � _, . b '_l Z�-L`,/8.2 3 =r- I S_ 2 3 -tt S- to 1. 8 9. 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R. V. LORD AND ASSOCIATES, BOULDER, COLORADO DO NOT WRITE IN THIS SPACE • j ' I KErvirED 7110-7� Work Description W:O. No. Date By Sheet 3% of ✓G D�'PJ'H - - -- 3.�r — AL4LI.LATJDwS O.m'L-_.424V � _t tN I ' I3Fr_.wE� _. rN 1 i I_ I pp , I} 1 i_i._.�. I , i i I ' _?_i._� I-_i. � 1 ._• `_' �---1 _�-. If .._ i _�_ �. � -�- 1_ _ � I I i L -- —I I ._. `_ 1�E�rN AT �DUT...: fROM1 F- . �7. .i��HYRRA.✓l C. RT�S pi -I ??� 71 - - — '— ----r + , — I I....__' i r - - -' - R. V. LORD AND ASSOCIATES, BOULDER, COLORADO •