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Stormwater Management Report.04.29.19886 • STORMWATER MANAGEMENT REPORT 10)14 OVERLOOK AT HILAND PARK TOWN OF QUEENSBURY, NEW YORK April 29, 1988 Prepared By: the LA group, p.c. 468 Broadway Saratoga Springs, New York 12866 • • HILAND OVERLOOK Stormwater computations for the proposed townhouse complex were conducted using the methods prescribed in the U.S.D.A. Soil Conservation Service Technical Release No. 55 (TR-55). A 25 year/24 hour type 2 event, having a 4.8" rainfall was the design storm used for the calculations. Existing Conditions The proposed townhouse site is located on the western side of Rockwell Road, along Hiland Park's eastern P.U.D. boundary. The site is primarily covered by meadow grasses with a narrow hedge row along the road frontage. The site is underlain by Plainfield and Oakville fine sandy loams, which have low runoff potential and high infiltration rates. These soils are in the SCS Hydrologic Soil Group A. Existing drainage divides are shown in Figure 1. Subarea 21 drains to the roadside swale on Rockwell Road. Subarea 20, the southern side of the project area, flows overland to the same drainage swale. Total peak predevelopment flow from both sources is 2.2 CFS; total volume is approximately .2 ac./ft., respectively, for the design event. Subarea 22, the west central portion of the site discharges over a broad 600' front west toward the golf course. Peak flow for the design event is 1.2 CFS, over the aforementioned slope. • Subarea 23, the northern end of the project area discharges 2.1 CFS at peak to an existing swale system on the edges of the golf course. Post Development The major post development drainage divides (see Figure 2) closely mirror the existing patterns just discussed. Total post development flow to the roadside swale (subareas 1,5,6,7,8 & 9) is 8.4 CFS. The additional runoff will be channeled to a controlled release basin which will be constructed as part of the abutting Fairway Court Subdivision. Peak outflow from this basin will be 4.8 CFS which approximates the total pre -development flow along this segment of Rockland Road. Outflow from the pond is controlled by a 12" Dia. CMP sloping at .007 ft./ft. At peak storage .19 ac.ft. of water will be retained. The inflow/outflow analysis for this pond is provided in the Appendix. Runoff from the west central portion of the site will be handled in two ways. Runoff from the rear lawns and roofs of the townhouses (labeled as Subcatchment #4) will be allowed to discharge naturally over a 540' segment of hillside. Runoff will be 1.4 CFS at peak, an increase of only .2 CFS. Runoff from the front of buildings and streets will be collected by 2 drain inlets (subcatchments #3 and #2) and piped (Reach 11) west to a shallow infiltration basin on the hillside above the golf course. Peak inflow to this basin will be 2.1 CFS. Runoff from streets and fronts of structures (subcatchments 10, 11, 12 and 14) in the north end of the project will be collected by a series of interconnected drain -inlets and piped (Reach 16) to a shallow swale which will discharge to a drainage ditch which flows west along the golf course. Runoff from Subarea 15 will be collected and discharged to the same drainage channel. • OTE ?OJECT:OVERLOOK -' STORAGE POND it 1 DATA --------------------------------------------------------------- ME INFLOW HR. CFS •--------------------------- OUTFLOW ELEVATION CFS STORAGE ACRE -FT. 10.0 0.0 0.0 347.6 0.01 10.2 0.1 0.0 347.6 0.01 10.4 0.1 0.0 347.6 0.01 10.6 0.2 0.0 347.6 0.01 10.8 0.2 0.1 348.1 0.01' 11.0 0.3 0.2 348.1 0.01 11.2 0.3 0.3 348.2 0.02 11.4 0.6 0.5 348.2 0.02 11.6 1.3 0.7 348.4 0.02 . 11.8 8.9 2,8 349.4 0.09 12.0 8.4 4.4 350.9 0.17 12.2 5.0 4.8 351.3 0.19 12.4 4.2 4.7 351.2 0.18 12.6 1.7 4.4 350.9 0.14 12.8 1.3 3.8 350.2 0.10 13.0 1.1 3.0 349.6 0.07 13.2 1.0 2.3 349.1 0.04 13.4 0.9 1.4 348.7 0.03 13.6 0.7 1.0 348.5 0.02 13.8 0.7 0.8 348.4 J.02 14.0 0.6 0.7 348.3 0.02 14.2 0.6 0.6 348.3 0.02 14.4 0.5 0.6 348.3 0.02 14.6 0.4 0.5 348.3 0.02 14.8 0.4 0.4 348.20.02 15.0 0.4 0.4 348.2 0.02 15.2 0.4 0.4 348.2 0.0:.• 15.4 0.3 0.4 348.2 0.02 /5.6 0.3 0.3 348.2• 0.05 15.8 0.3 0.3 348.2 0.02 16.0 0.3 0.3 348.2 0.02 16.2 0.3 0.3 348.2 0.02 16.4 0.3 0.3 348.2 0.02• 16.6 0.2 0.2 348.2 0.01 16.8 0.2 O.S. 348.1 0.01 17.0 0.2 0.2 348.1 0.01 17.2 0.2 0.7 348.1 0.01 17.4 0.2 0.2 343.1 0.01 17.E 0.2 0.2 348.1 0.01 17.8 0.2 J.'J 348.1 0.01 18.G 0.2 0.2 348.1 0.01 18.2 .3 0.2 348.1 0.01 18.4 0.2 0.2 348.1 0.01 18.6 J.2 0.2 348.1 0.01 18.E 0.2 0.2 340.1 0.0'_ 19.0 0.2 0.2 348.1 0.01 19.2 0.2 0.2 348.1 0.01 _9.4 J.2 3.2 348.1 0.01 19.6 0.2 J.=l 348.1 0.01 19.8 0.2 0.2 348.1 0.01 20.0 0.2 0.2 348.1 0.01 • •DATE: _/_/_ PROJECT:OVERLOOK SHEET: OF --------------------- EXISTING SUBCATCHMENT --------------------- SUBCAT # 1 AREA= 1.93 ACRES CN= 67.77 TC= 17 MIN PEAK FLOW= 3.4 CFS RAINFALL= 4.8 INCHES VOL= .25 AC.FT. SUBCAT # 3 AREA= .55 ACRES CN= 71.1 TC= 18 MIN PEAK FLOW= 1.1 CFS RAINFALL= 4.8 INCHES VOL= .06 AC.FT. SUBCAT # 5 AREA= .7200001 ACRES CN= 70.6 TC= 8 MIN PEAK FLOW= 1.8 CFS RAINFALL= 4.8 INCHES VOL= .1 AC.FT. SUBCAT # 7 AREA= .3 ACRES CN= 57.3 TC= 8 MIN PEAK FLOW= .4 CFS RAINFALL= 4.8 INCHES VOL= .01 AC.FT. SUBCAT # 9 AREA= .9399999 ACRES CN= 53.4 TC= 19 MIN PEAT{ F LOW= .7 CFS RAINFALL= 4.8 INCHES VOL= .04 AC.FT. SUBCAT # 11 AREA= .17 ACRES CN= 80.4 TC= 6 MIN PEAK FLOW= .7 CFS RAINFALL = 4.8 INCHES VOL= .02 AC.FT. DATA SUBCAT # 2 AREA= .65 ACRES CN= 66.2 TC= 22 MIN PEAK FLOW= 1 CFS RAINFALL= 4.8 INCHES VOL= .06 AC.FT. SUBCAT # 4 AREA= .8600001 ACRES CN= 57.3 TC= 6 MIN PEAK FLOW= 1.4 CFS RrAINFALL= 4.8 INCHES VOL= .05 AC.FT. SUBCAT # 6 AREA= .55 CN= 67.1 TC= 9 MIN PEAK FLOW= RAINFALL= VOL= .05 SUBCAT # 8 ACRES 1.1 CFS 4.8 INCHES AC.FT. AREA= .32 CN= 72 TC= 6 MIDI PEAK FLOW= RAINFALL= VOL= .03 ACRES 1 CFS 4.8 INCHES AC.FT SUBCAT # 10 AREA= .18 ACRES CN= 73.^ TC= 6 MIN PEAK FLOW= .6 CFS RAINFALL= 4.8 INCHES VOL= .01 AL.77. SUBCAT # 12 AREA= 18 ACRES CN= 76 TC= 6 MIN PEAK FLOW= .7 CFS RAINFALL= 4.3 INCHES VOL= .02 AC.FT. I SUBCAT # 13 AREA= 2 ACRES CN= 68.6 TC= 6 MIN PEAK FLOW= .5 CFS RAINFALL= 4.8 INCHES VOL= .01 AC.FT. SUBCAT # 15 AREA= .6600001 ACRES CN= 63.7 TC= 10 MIN PEAK FLOW= 1.1 CFS RAINFALL 4.8 INCHES VOL= .05 AC.FT_ SUBCAT # 20 AREA= 2.13 ACRES CN= 49 TC= 17 MIN PEAK FLOW= 1.2 CFS RAINFALL= 4.8 INCHES VOL= .08 AC.FT. SUBCAT d 22 AREA= 2.35 ACRES CN= 49 TC= 22 MIN PEAK FLOW= 1.2 CFS RAINFALL= 4.8 INCHES VOL= 9.000001E-02 AC.FT. SUBCAT 0 14 AREA= .3 ACRES CN= 72 TC= 6 MIN PEAK FLOW= .9 CFS RAINFALL= 4.8 INCHES VOL= .03 AC.FT. SUBCAT # 16 AREA= 1.06 ACRES CN= 57.8 TC= 18 MIN PEAK FLOW= 1.1 CFS RAINFALL= 4.8 INCHES UOT.- A A!r %�r SUBCAT # 21 AREA= 2.38 ACRES CN= 49 TC= 31 MIN PEAK FLOW= 1 CFS RAINFALL= 4.8 INCHES VOL= 9.000001E-02 AC.FT. SUBCAT 0 23 AREA= 3.11 ACRES CN= 49 TC= 12 MIN PEAK FLOW= 2.1 CFS RAINFALL= 4.8 INCHES VOL= .13 AC.FT. SUBCAT # 30 �-- �1-4 -rYd r�i-lD t2oM A?EA= 2.17 ACRES CN= 63.6 TC= 11_ MIN PEAK FLOW= 3. CFS .RAINFALL= 4.8 INCHES VOL= .23 AC.FT. L • --------------------- EXISTING ROOTING DATA --------------------- REACH # i PEAK FLOW= 3.1 CFS MAX. FLOW POSSIBLE= 3 CFS MAX. WATER DETAINED= .03 AC.FT. REACH # 3 PEAK FLOW= 1.1 CFS MAX. FLOW POSSIBLE= 3 CFS MAX. WATER DETAINED= 0 AC.FT. REACH # 10 PEAK FLOW= 1 CFS MAX. FLOW POSSIBLE= 3 CFS MAX. WATER DETAI,".rED= 0 AC.FT. REACH # 12 PEAK FLOW= 2.8 CFS MAX. FLOW POSSIBLE= 2 CFS MAX. WATER DETAINED= .05 AC.FT REACH # 15 PEAK FLOW= 2.1 CFS MAX. FLOW POSSIBLE= 45 CFS ?''.AX. WATER DETAINED= 0 AC.FT. REACH # 2 PEAK FLOW= 2.8 CFS MAX. FLOW POSSIBLE= 2 CFS MAX. WATER DETAINED= .05 AC.FT. REACH # 4 PEAK FLOW= 2.8 CFS MAX. FLOW POSSIBLE= 4 CFS MAX. WATER DETAINED= 0 AC.FT. REACH # 11 PEAK FLOW= 2.1 CFS MAX. FLOW POSSIBLE= 5 CFS MAX. 'WATER DETAINED= 0 AC.FT. REACH # 14 PEAK FLOW= 3.1 CFS MAX. FLOW POSSIBLE= 3 CFS MAX. 'WATER DETAINED= .05 AC.FT. -------------------- EXISTING MEMORY DATA -------------------- MEMORY 1 PEAK FLOW= 3.5 CFS MEMORY 3 PEAK FLOW= 6.3 CFS --------------------- EXISTING PONDING DATA --------------------- POND # 1 PEAK OUTFLOW=s 4.76 CFS MAX. WATER STORED= .19 AC.FT. MEMORY 2 PEAK FLOW= 10 CFS i -\�,. 15500 ` \. N. NNNN \ \ \ \ It \ sa \ / \ \ 1 \ �♦ \ \\ \� �` \ -f36Q \. \N. 7g� • i - Ord; - n\ \ i I \ ,I 1' • \ '--""'.e'er 1821�jj � �• '� � � i 1 �\ � � \ \ \ \ \ \ \ �-♦ r' `.'r I„� i/ vI » �. �� � i.� �� 1 • �. i.� �a Y� � ..ter.. � �. �r� � f+� �•.r � _ �t0 �i ^^. � — �— � 'ir"t Al'1 \ \ 16 cz 80 -,Ad�.�'1'ffeZYK.��`v+�C""��'�•r�r— �.�