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HomeMy WebLinkAboutDrainage Reports - 05/10/1991 (2)FINAL DRAINAGE REPORT lib OVERLAND HILLS FIRST FILING JANUARY 16, 1991 PREPARED BY STEWART & ASSOCIATES, INC. w SITE LOCATION: The site is located in the Northwest a of Section 33, Township 7 North, Range 69 West of the Sixth P.M., Fort Collins, Larimer. County, Colorado. The area is 4.1842 acres more or less. It.is located in the Spring Creek Drainage Basin. The site is bounded on the East by the Springfield Sixth Subdivision; the South by Springfield Subdivision Fifth Filing; part of the West and North sides are undeveloped. There is a single family residence located to the Northwest of the site. EXISTING CONDITIONS: The site drains in three directions due to the South side being on top of a hill. The West 1.1 acres drains West to Spring Creek. The existing slope is 10%. The East 2.7 acres drains to Springfield Sixth Filing. The existing slope is 1.7%. The North 0.3 acres drains to the North. The existing slope is 2.0%. There is no existing offsite runoff across the site, excepting for Spring Creek on the West boundary line. Total existing site runoff is Q2 = 1.79 c.f.s.; Q770 = 3.79 c0f.s.; Q1p0 = 7.82 c.f.s. Basin "A" runoff, being the West 1.1 acres, is Qp = 0.69 c.f.s.; Q110 = 1.66 c.f.s.; Q10 = 3.56 c.f.s Basin "B" runoff being the EastL.7 acres, is Q2 = b.94 c.f.s.; Q 0 = 1.35 c.f.s.; Q10 = 2.7 c.f.s. Basin "C" runoff, being the North b.3 acres, is Q2 = U.Q3 c.f.s.; Q10 = 0.78 c.f.s.; Q100 = 1.56 c.f.s DEVELOPED CONDITIONS: The developed site is divided into three drainage basins. These basins are shown on the included grading plan. Basin I, which is all of Platte Place East of Platte Court and the South Half of Platte Place along with lots 1, 2, 3 and 4 will drain East to Platte Drive, then to the detention pond constructed on Tract "A" of the Springfield Subdivision Sixth Filing. The area is 1.5 acres. Runoff to Platte Drive is Q2 = 1.28 c.f.s. Q10 = 2.21 c.f.s.; and Q100 = 4.41 c.f.s. Basin II, which :i.s-. lots 5 and 6 will drain West directly to Spring Creek. The area is 1.1 acres. Runoff to Spring Creek is Q2 = 1.43 c.f.s; Q10 = 2.53 c.f.s.; and Q100 = 5.45 c.f.s. Basin III, which :i,s� lots 7, 8, 9, 10, and all of Platte Court and the North half of Platte Place West of Platte Court will drain to the Tract "A" detention pond. The runoff from the front portion of the lots and from the streets will drain to a sidewalk culvert and drainage pan which will flow east in an easement between lots 8 and 9. The concrete pan will be extended into the detention pond to connect with the existing pan system. The area is 1.6 acres. Runoff to Tract "A" is Q2 = 1.6 c.f.s.; Q10 = 2.7 c.f.s.; and Q100 = 5.5 c.f.s. There will be no detention for lots 5 and 6 because of proximity to Spring Creek. The balance of the project will be detained in Tract "A". The required detention is 14,998 c.f.s. The existing Tract "A" detention Overland Hills First January 16, 1991 Page .2 Filing Drainage Report pond has a capacity of 258,330 cubic feet to a spillway elevation of 41.20. The area of the 41.20 high water line contour is 107,800 square feet. We plan to raise the spillway by 0.20 feet which will add 21,560 cubic feet to the volume of the detention pond. We plan no revision to the existing constructed outflow of the pond. A copy of the original Tract "A" pond report and plan are included for your review. A plan of the revised Tract "A" is also included. - The Spring--Greek-100-year floodway-and 100 year floodplain flows —Sou- - vh to North across the West end of our subdivision. The 100 year floodway and 100 year floodplain were taken from Figure 3, "Floodplain Analysis for Overland Consultants, Hills Subdivision Filing'l and 2", prepared by Resource lqqj Inc., dated November 12, 1990 and revised December 27, 1990. it, The East line of the 100 year floodway , is the East line of Tract"A" t shown on the final subdivision plat on the grading plan. The 100 year ev floodplain is shown in an easement over lots 5 and 6 for drainage and �'p �� utilities. }�^ . Franklin D. Blake, P.E. & L.S. N�'-CYO ••e••• ',? f,•..DS 15'ER"'r 3_ 3 9 ~• compurATIONS ties H. Stewart & Associates, Inc. 214 N..Howes St. Fi. Collins, CO 60521 (30) 482-9331 Date Client: Sheet No. of A By: -Date Project: .'Job No. ject • m COMPUTATIONS imes H. Stewart & Associates, Inc. 214 N..Howes St. Ft. Collins, CO 80521 (M) 402-9331 Date Cliene, Sheet No. z of !!f, Ad By: Date- Project: Job No. bject '�� COMPUTATIONS Imes/H-.,Stewart & Associates, Inc. 214 N..Howes St. Ft. Collins, CO 80521 (30) 482.9331 Date Client:- irf/irl S�l�D�� Sheet No. "3, of _� Date Project: I r r r� i A � I Me COMPUTATIONS lames ,H, .� Stewart & Associates, Inc. 214 N,,Howes St. 'Ft. Collins, CO 8U521 (3U3) 482-9331 iy: -/ac/ Date Client: Client:-_ ,�ii�-� ��yd/'� -- � Sheet No. of :hkd By: Dato Project: �l�C%�/7� fy/�/.� Job No. subject a�Cd� /h'Ji ✓ I , 000, - - _ -- —- - v i I op IAO -a J-- .... r. .... z_ - - Qa �- L•5. - c s . - - - _ _. ._ I I 1 i , I I A ZY COMPUTATIONS James H. Stewart & Associates, Inc. 214 N.. Howes St. Ft. Collins, CO 80521 (303) 482-9331 3y: Date Client: 115-1zle-k7 t. Sheet No. of -1 likd By: - Date- Project: Job No. I >Ubject � r - COMPUTATIONS Jallw-q H- Sipwar, JL ms I I I By: --4G� ChI(d By: I 3ubject WU a vat 11U. 2141%.flowesst.. Ft. Collins, C08u521 Date Client: —Sheet No Date Project: Job No. (303) 482-9331 G of 4 compu-rATIONS. James //H.--Sttewart & Associates, Inc. 214 N..Howes/St. Ft. Collins, CO 80521 (3Q3) 482.9331 By:�4_ Date 9D Client:. / Sheet No. � of Chl<d By: Date Project: O`�/�Vld "!/ Job No. Subject compvrATIQNS . JamesH. Stewart & Associates, Inc. 214 N..Howes St. Ft. Collins, CO 8U521 (3U3) 482.9331 By: �./�4;L t Date % O O Client: 14;5O,7 m��9e Sheet No. of Chl<J By: Date Project: Job No. Subject �� aTl��7S — i�iii�/ �,✓ - � I / I • I I n C ZVI e I I � l_ - -s1— 36 / 3I 1 5r o0v L TIdT 9> G 5 ... - 1- 5o 7-1 .zIS o : 'fit I i I ; I , : I I I i I I , k- STEWART&ASSOC(ATES Consulting Engineers and Surveyors July 2, 1990 Mr. Rex Burns Larimer County Flood Administrator P 0 Box 1190 Fort Collins, CO 80522 Dear Rex: This is an update of the detention facility, for Springfield Subdivision dated January 14, 1980. The detention pond is located in an old gravel pit at the Northwest corner of Springfield Subdivision, Sixth Filing. The subdivision contains 51.35 acres that drain to the detention pond. The site is in the Spring Creek drainage basin and the Mass Diagram method of required detention volume was used. The required detention is 5.9 acre feet and the allowable outflow rate is 7.19 cubic feet per second. The outlet pipe through the berm will be a 12 inch diameter N-12 A.D.S. pipe which will restrict the flow to the two year historic quantity of 7.19 c.f.s. The outflow will flow in an open swale Westerly to the existing Spring Creek thalweg. The swale centerline will be forty feet South of the North line of the Northwest } of Section 33-7-69. This places the swale between the future South curb and the future South sidewalk of Horsetooth Road. The calculations of the runoff quantities and the capacity of the improvements are enclosed as a part of this report. Also, enclosed are the grading plan of the detention pond and the plan and profile of the outlet swale. If you have any questions concerning the plans or the report, please call. Sincerely, Richard A. Rutherford, P.E. & L.S. President lkk enclosures James H. Stewart and Associates, Inc. 214 N. Howes Street P.O. Box 429 Ft. Collins, CO80522 3031482-9331 SUHJEC;I y���ldJle�IELD—Jl1C2li_F14LN�2--. BY--_K J _—.UAIE LLLJ190 SHEET NO.-------- ---------------- --_: PROJECTNO.---- TM1; (mlv.) Z cf c A c.F.S. V oc.Um's cv.Fr /0 7.Z . /.Lsx p.¢s x s/.3,5' IZ 4; 74U ZO S,Z ZS•88 /S0. Z. / SO, Z40 3o ¢•ZZ.18, 340 �4o 60 Z•(v 7S. I Z70, 3(oo 90 /.9 S4.9 Z96, ¢GO Iz0 /14s '. /So � •os / % 301. (.So ssoou 30.3 3 Z 7, Z-4.0 i96, }(10 30 0, 000 Z So, 000 . \ 1h IL d` M J Q 3 0` 2.00,000 N iJ LL 0 � 7 a lso,000 100,000 H w 50, 000 p O 10 Zo 30 4o 38,eu 60 90 -77//k S C M i.u.) IZD 7,19 18d AU pJ t\,I `J CAv-,LIL(GJ=C L-_LZ t37_-1-'�c 1. L/mac•_—. ur.i�=L=IF-/v j —D—F,—rr-,w J.2tv-_QL�Q11SHEET NO. -------- PROJECT NO.-- -- AP—eA.; S/.3SA,. H�JT T� = 1.87(/•l-0.z) 31ooI/t- S$ Miv, 1.Z'A' Misr. Q i yR, = O. Z X O. 7 k S /. 3,5 = 7, 19 L , F S, 0 H�sr• Qioye = O.Z,A ! Z X S/.3S = /Z.3Ze•F.r. Hrjr. Qiooy,e/= /•zS XD.Z x /,9 nS/•3.5 > z4.39 c.F.s. G F.S. CALc• F,evAl 36PAe4r6 SAVA4f, ©uTLE T PIPE 37,ZS M, W, L: = 4-/.Z0 U = - 0. (, j�9 tih - D. 6 2 x 3Z•L x 3.95 - 9 S7 A= Q = _ . 9 57 — 0.?3 �Ez Us6 IZ'' P.V.G. S wALC SECTioAl 1.49 x 4,0 l„4_)L/j / �V, ok 0 0 ZS X 8/ �4/ X 0.003) = 8, 10 c.F.S. Sit- f111N iib/K '� I',�1{ flrn0l� I111 �� III Jill II ` LVve I,h e1 a' (Imdr Ms J6' high Used to intercept and drain small amounts of sediment from leaving the cotuo-u n sire and b decrease the speed of runoff. The sift fence u made of synthetic fifer fabric or burlap supponed by pose, and some imus, wire fence. The bottom edge of ere farr fabric u buried in the dirt on the upslope side to keep it from washing cut. Sit fence can trap more suspended s diment than „arw bale. Inspection and repair may be necessary after heavy s. o a SEOTEM� /990 /NO YEA.P Fi�NA✓ .ONO FCcbIIfCFiN W JbKEN Fran �� v E 3, FLucto�N t %UdG VS/S FO? 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