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HomeMy WebLinkAboutDrainage Reports - 10/01/1977�'•�-ari'._. :5''.. ,.... .. iw.'?a+,aCi�+ni&rs':<,-„'�PbIT'r'"+f�Fl�+'12c���msd`�Y'i"'�4z`.��.?�:•�'M1 „a�i-:A: + N r, r 17�4 y,-a�r°4� lu ''? t %Afx• - trts: i.�. - i ' ..r' ''„� r -w • � [ .-�nw-F-°"'FT E"' o' C .�.wr ...•rk..�v`^��—tea.: "'' c� ". � ..t� �5' .t-' i,§4Y� �a:. 3a c.•3'j9r#,r^`[^M'-S` r' v, �[ ,{:STORMDRAINAGE STUDY _ _y _-°FOR -. BROWN :FARM, FOURTH FILING - - - - '-.•+.- s.: u'_•�--.-T. -__ _ :�r_a^'---^•...i � --+... . -...-.ter-=� .-..r.- .� .. _.. _ .. ._. _ ...._�-'�_. -ter.: • .- - FORT COLLINS, _ COLORADO- OCTOBER, 1977 M&I consufting engineers 4710 South College Ave. Fort Collins, Colorado 80521 Telephone (303) 482-8249 November 7,.1977 .Wheeler Realty 1331 8th Avenue Greeley, CO 80631 ATTN: Mr. Dan Wheeler Dear Dan: Presented within is a Storm Drainage Report for the Fourth Filing in Brown Farm Subdivision, located in Fort Collins. This report conforms to the subdivision regulations of Fort Collins and F.H.A. All calcu- lations pertaining to this report are available upon request at our .office. Please feel free to contact us with your questions or comments. Very truly yours, M & I, INC. / f� `'John R. Hutchinson ;Jame" M: ils, P.E.-L.S. V' JRH/ms Enclosure TABLE OF CONTENTS I. Page No. 1 II. STUDY AREA 1 III. EXISTING STORM DRAINAGE FACILITIES 1 IV. DESIGN CRITERIA AND REQUIREMENTS 2 V. RECOMMENDATIONS AND CONCLUSIONS 3 EXHIBIT NO. 1 "Historical Flows" EXHIBIT NO. 2 'Design Flow" EXHIBIT NO. 3 11100 Year Storm Effects" EXHIBIT NO. 4 "Intensity Duration Curves" I. INTRODUCTION The purpose of this report is to supply the developer with recommendations on procedures for proper control and disposal of storm water runoff in Brown Farm, Fourth Filing, Subdivision. The scope of this report includes a Storm Drainage analysis for the flows generated by this property in both.its historical and improved condition. This analysis consists of the following items: 1. Established rainfall intensity duration.curves 2. Storm runoff flows and their directions in the designated streets. 3. The size and slope of storm drains required. 4. Size and locations of culverts and detention ponds. II. STUDY AREA The study was performed on Brown Farm, Fourth Filing, located in Fort Collins, Colorado. Exhibit #1 indicates the main historical basin and, the quantity and direction of flow during a 2-year storm. The four main design basins, flows resulting from 2 year and 50 year storms, detention ponds, and culvert sizes and locations, are illustrated in Exhibit #2. The effects of a 100-year storm are accounted for in Exhibit #3. III. EXISTING STORM DRAINAGE FACILITIES Presently all storm water runoff is intercepted by the Pleasant Valley and Lake Canal which lies along the eastern boundary line of the Fourth Filing. The Pleasant Valley'and Lake Canal will also accept improved storm runoff from the proposed subdivision. -1- Y IV. DESIGN CRITERIA AND REQUIREMENTS The amount of storm water runoff for the area, individual basins, and the streets was determined by the Rational Method. This procedure is common.iy employed in the design of borrow ditches, storm sewers, and combined sewers. The Rational Method equates the design peak flow to the area, amount of rainfall on that area, and a multiplier that is determined by the physical characteristics of the area under study. The design of all storm sewer facilities presented in this report is based on the rainfall intensity duration curves developed by the City of Fort Collins Engineering Department (see Exhibit #4). The initial drainage system should be designed to accomodate the runoff from a 2-year storm by means of utilizing the maximum capacity of the streets, overland swales, and if necessary, underground conduits.' The City of Fort Collins requires that an improved site must limit its runoff to the amount resulting from a 2 year frequency storm, occurring while the site is in its natural state. To accomplish this, it is usually necessary to design a detention pond with the total storage capacity of the difference.between 50-year storm runoff on the developed area and the historical flow, as defined earlier. An outlet structure ' is designed to limit the flow to the historical runoff value. The major drainage system must be designed to handle a 100-year storm without extensive property damage or loss of life. Areas which may be susceptible to flooding in such a storm must be examined. For purposes of this analysis, it will be assumed that the storm sewer system has been blocked and rendered ineffectual. Floor elevations should be set to allow proper drainage between and around these houses without flooding. The ponding elevations, capacities of the channels, pipe capacities are determined by Manning's formula, which equates a constant, a roughness factor, the area of the channel, the hydraulic radius and the slope to the capacity of the channel or pipe. -2- V. RECOMMENDATIONS AND CONCLUSIONS Historical, improved and 100-year flows are shown on Exhibits 1, 2, and 3 respectively. The offsite area to the west of this site will be contributing runoff. In order to intercept and control this water, it is recommended to construct a shallow swale which will run along the western boundary line in a northerly direction to the Pleasant Valley and Lake Canal. With the development of this off -site area the swale will be relegated to only handling the runoff from the rear areas of lots abutting the eastern boundary line. Two detention ponds must be constructed in order to properly limit the runoff to that of the 2-year historical flow. Pond "A" will have a capacity of 0.66 acre feet and an outlet of 1.27 cfs; Pond "B" - 0.84 acre feet and 2.00 cfs. Ideally one larger pond should have sufficed, but with this particular lot and street configuration, two smaller ponds are necessitated (see Exhibit #2). Only two areas might be subjected to flooding during a 100-year storm - The Northeastern Cul-De-sac, and the intersection of Streets A and B. Both areas have adequate capacity and all houses will remain above the ponding level at both locations (see Exhibit #3). This drainage design will satisfy all hydraulic considerations.as well as governmental regulations, in providing this future community with both a safe and equitable solution to the problem of handling stormwater runoff. -3- 4 BROWN FARM 4th. FILING / EXHIBIT No. J r HISTORICAL FLOW P E'q SgNT G Cq Nqt m, BAINI AR ACRES o •4.50 C..S. W i i �\ } AL • 5.00 0 y pO O < O I 1 \\ LEGEND 'I DESIGNATES DRAINAGE BASIN �- INDICATES DIRECTION OF FLOW B QUANTITY OF FLOW IN CUBIC FEET PER ! SECOND ' C.F.S.' DRAKE ROAD ` Owl BROWN FARM 4 th. FILING J EXHIBIT No. 2 r DESIGN FLOW a A j %74%7t: A s c6« .r D1l CAP qF AL -?.60 F6. DRAKE_ c a 1 15 I, 7 T I, DRAINAGE SWALE DETAIL ��gSgNT ' s... t4 rr �gNgt 150 PIPE SLOPE Loo x - DETENTION POND "A" 14C).a 0.66 ACRE FEET IE" i E oPl3i LEGEND ARE Q eo • .Ra. I' DESIGNATES DRAINAGE BASIN �— INDICATES DIRECTION OF - FLOW B QUANTITY OF FLOW jNC.►.e. CUSjC FEET PER SECOND �\ \ — PROPOSED IMPROVEMENTS 12 � 6L .DO% " \ DETENTION POND "B" 0.84 ACRE FEET - BASIN 4 • %AREA"0.37 ACRES 60.0. �C.F.s. ©� esvo Apr. BROWN FARM 4 th. FILING EXHIBIT No. 3 EFFECTS OF A 100 YEAR STORM 9 lmimv,&vA%h:,q 8' VA PAN i Y CAL) ,� LL of O LL 11/ SACI 1 PONDING ATION• 8140. O W AX. DEPT .81, Pl , m < ww •oG W O<0 m o (So* •1 ❑ )I CAP QF SWAL ' (9. .F.S. DRAKE a IS' T 7 DRAINAGE SWALE DETAIL gSgNr V .�\q�`Fr �... kF C4V4t DETENTION POND "A" 0.66 ACRE FEET �--� 12" i OE 0100. LEGEND I — PROPOSED IMPROVEMENTS PONDING AREA DETENTION POND"B" 0.84 ACRE FEET ©MEA .,,.... z c m co PRECIPITATION - INCHES PER HOUR v N m 000e< m v 0000 a cd 7° o i Q Of m a m o� o7 J mm 7Coa0 ��xcnNa�n cy' C 10zmWav m O�'tD vm mz0 a ova Z Z O m a, -f z O < m m m vov m Z cl,zIV K �2 o N a' o w m -q < O r o m�m _r C C C i C Z y fn cczim a' al n _ O O m 70 wDc Z r O 0 0No C D O D v a0D � m O v 0 00