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HomeMy WebLinkAbout601324001 Drainage Reportwww. n ti4u. com NORTHWESTERN' TERRITORIES, INC. 717 SOUTH PEABODY STREET, PORT ANGELES, WA 98362 _ Engineers · Land Surveyors · Geologists Construction Inspection · Materials Testing (360) 452-8491 1-800-654-5545 FAX 452-8498 E-Mail: info@nti4u.com DRAINAGE & EROSION CONTROL REPORT FOR A RESIDENTIAL PARCEL LOCATED IN SECTION 32, TOWNSHIP 26 NORTH, RANGE t WEST, W.M'i Prepared for ' Ron &'Monika Shepard Prepared by Robert A... Leach, 'P.E: a n d NoAhwestern Territories, Inc. 717 South Peabody PoA Angeles, WA 98362 NOVEMBER 4, 2001 I. INTRODUCTION Northwestern Territories, Inc. (NTI) was hired by Ron & Monika Shepard t° develop a drainage plan for their proposed home. site. As part:of this.analysis,~a stormwater collection and infiltration system design was' created to simulate the collection of stormwater runoff from the roof of-the propoSed buildings, the gravel driveway and open area. II. DESCRIPTION OF SITE Recently approximately one acre of wooded area has been cleared for the access driveway and the proposed home site. The_site is located on TOandos Peninsula and is bordered by Dabob Bay on the west: The site is accessed via Sierra Trail from the east. The site slopes down to the west and east. The bluff line is located approximately 900 feet east of the high tideline. The westerly Portion ranges in slope from 30 to 55% down to the beach. While the easterly portion rangesin slope from 5 to 15%. The home site is in the northwest corner of the easterly portion. The US Department of Agriculture Soil Conservation Service clasSifies the soil in the home site area and access driveway as Hoypus (HUD) gravelly loamy sand, a hydrologic group A soil. II1. METHODOLOGY & CALCULATIONS Jefferson County requires the use of the Department of Ecology (DOE) Stormwater Manual which uses a 2, 10 & 100 year.storm frequency, 24 hour storm-duration and the Santa Barbara Urban Hydrograph (SBUH) method of simulation to apProximate the increase in storm drainage runoff resulting' from a development. The site has been modeled using the Water Works Versio'n 4.13i Computersoftware from Engenious Systems. This program uses the (SBUH) Method of simulation as required by the DOE Manual. The design is based on land use and_size of drainage collection area. The recommended drainage system for this site is infiltratiOn due to the soil type. A drainage plan and full simulation report created by Water Works are included in the appendix. The following parameters were used for the primary variable's input, values thatwere used in this analysis. · 2 year, 24 hour rainfall for Toandos Peninsula - 3.50" per NOAAPrecipitation atlas 10 year, 24 hour rainfall for Toandos Peninsula = 5.00" per NOAA precipitation atlas 100 year, .24 hour rainfall fOr Toandos Peninsula - 7.00" per NOAA precipitation . atlas Impervious Areas: Roof Curve Number = 98 Gravel Roadway = 76 Pervious Areas: Lawn (Good Condition) Curve' Number = 68 Wooded = 42 Storm Type = SBUH Type lA; duration - 24 hoUrs Time of Concentration calculated by software based .upon .existing drainage collection facilities. land assumed · Infiltration Rate = 4.56 minutes / inches - mid range for SOil type. Pre-development site is 9.09 acres of pervious and O,00acres of impervious. Developed site is 8.09-acres of undeveloped wooded area, 0.6i acres of. pervious and 0.39-acres of impervious. · Collection Devices - gutters,~ down spouts & drainage ditches. Disposal Device = drywells corresponding to the 2, 10 and 100 year pre- development 24 hour storms. Due to the topography, the driveway will need to be graded to drain-into the ditch. IV. EROSION &'SEDIMENT CONTROL The siltfence to be placed along the easterly .boundary of new constrUctiOn 'prior to breaking ground. Also haybales are to be placed.in ditch line every .100 feet. prior t© the removal of the siltfence and haybales, the ditch needs-to be hydroseeded. V. CONCLUSIONS Due to the limited downhill one space and the setback requirements from structures and drainfields, all of the runoff from the buildings, open area. and driveway Will be drained into the driveway ditch line. To dispose of the runoff, d~rywells Will be placed in. the ditch line. Since, the grade of the driveway is approximately 15 percent and drywells must be installed level, the drywells willbe placed intermittently along the length of the driveway. Check dams will be placed eVery 30 feet, in front of each drywell, to minimize runoff velOcity. A total of 50, 2 feet wide'by 3' feet deep by 1-1 'feet long drywells, will be installed to provide the required infiltration of runoff caused by the change in land use from wooded to gravel roadway. Roof runoff will be collected, .stored, treated and used as drinking water on the site. Even though this will dispose of the-majority of the additional runoff created bythe .3 development, an emergency overflow system is reqUired assuming the drinking water storage system is full when the 100 year storm event Occurs. The 6". HDPE emergency overflow pipe will drain into the driveway ditch line. VI. LIMITATIONS This report has been prepared for the exclusive use of Ron-& Monika Shepard for their proposed design of the Alaska Power and Telephone Expansion site. The recommendations in the report aPply only to the property that was examined, and they are not applicable to other areas. The investigation and recommendations contained in this report are based upon site conditions as they existed at the time of our site inspections. During construction, if subsurface or other conditions are discOvered that are significantly different from those' described in'the report, NTI should be .advised at once so that we can review the conditions and reconSider our recommendations, where necessary. Unanticipated soil Conditions are commonly encountered on construction sites, especially when the topography has been altered years ago. SUch Unexpected conditions frequently require that additional expenditures be made' to attain a .properly constructed project. We recommend that a contingencY be established in the project budget and schedule to .cover unexpected conditions. Within the limitations of scope, schedule and 'budget, our services have been executed in accordance with generally accepted professional engineering principles and practice: This warranty is in lieu of all others, either expressed orim'plied. NORTHWESTERN TERRITORIES, INC. Robert A. Leach, P.E. Principal Design Engineer Kate Waddell, B.S.C.E., E.I.T. Engineering Technician EXPIRES 12/30/2002 11/4/01 . . APPENDIX . oo '-x 40 .... ..35 ._~.30 2520 50N I 4o\ 55 45 40 15 2f S~_AT ., /-B [ t,~ , 35 30 - CENt 25 61 45 40' fRIDAY I-~AR ')OR STANL i ! 17.5 ',,,,,, 25 · g SEAT TACOMA ABER! 50 NI .. :55 .": 35' 15; ~075 _ __70 15 8O 85... 90 100", 100 ' O0 --,90 II IOO ~jr I00 Preconstruction Post Construction 6 mo Basin ID = 6m Basin ID = 6m+ Ap = CN= Ap = CN= Ai = CN= Ai = CN= Rain = Rain = Tnp= Tnp = Tni = Tni = 2 yr Basin ID = 2y Basin ID = 2y+ Ap = I .oo CN= ~,2 Ap = o. ~-, I CN= Ai = ON= Ai = ~ .'~t ON= Rain = 3, ~c:, Rain = '~,'~-'-c~ Tnp= I ~2- 5' Tnp = ~.9. ~5~ 2. Tni= Tni= ~0,~ 10 yr Basin ID = 10y Basin ID = 10y+ Ap =' I.oo ON= ~/2- Ap = o,c0 t ON= Ai = CN= Ai = o o~ CN= Rain = 6ooo Rain = ,~. oo Tnp= /'g ;z., 5" Tnp = ,A~. e~5-~- Tni = Tni = /o ~ '~ G'~ 25 yr Basin ID = 25y Basin ID = 25y+ Ap= ~ CN= Ap= CN= Ai = CN= Ai = CN= Rain = ~ Rain = Tnp= Tnp = Tni = Tni = 100 yr Basin ID = 100y Basin ID = 100y+ Ap = ~o c,o CN= ~ 2. Ap = ~)o~ / CN= Ai = CN= Ai = ,~-'~,~/ ON= Rain = '1 ,~o Rain = ?. Tnp= /~, 7..,d' Tnp= Tni = Tni = /o. b"~,? _ Other: Type lA Storm SBUH method G:\GEN~BOB\Storm table.wpd 11/4/01 11:25:30 am Shareware Release DRAINAGE AND EROSION CONTROL PLAN RESIDENTIAL LOT FOR: RON & MONIKA SHEPARD page 1 BASIN SUMMARY BASIN ID: 100yr SBU}{ METHODOLOGY TOTAL AREA ....... : RAINFALL TYPE .... : PRECIPITATION .... : TIME INTERVAL .... : ABSTRACTION COEFF: TcReach - Sheet TcReach - Sheet PEAK RATE: 0.07 NAME: 100 year pre construction 1.00 Acres BASEFLOWS: 0.00 cfs TYPE1A PERV 7.00 inches AREA..: 1.00 Acres 10.00 min CN .... : 42.00 TC .... : 182.50 min 0.20 L: 200.00 ns:0.8000 p2yr: 3.50 s:0.0500 L:1500.00 ns:0.8000 p2yr: 3.50 s:0.1500 cfs VOL: 0.08 Ac-ft TIME: 1320 min IMP 0.00 Acres 0.00 0.00 min BASIN ID: 100yr+ SBUH METHODOLOGY TOTAL AREA ....... : RAINFALL TYPE .... : PRECIPITATION .... : TIME INTERVAL .... : ABSTRACTION COEFF: TcReach - Sheet TcReach - Sheet impTcReach - impTcReach - PEAK RATE: NAME: 100 year post construction 1.00 Acres BASEFLOWS: 0.00 cfs TYPE1A PERV 7.00 inches AREA..: 0.61 Acres 10.00 min CN .... : 68.00 TC .... : 28.85 min 0.20 L: 200.00 ns:0.1500 p2yr: 3.50 L:1500.00 ns:0.0600 p2yr: 3.50 Sheet L: 50.00 ns:0.0110 p2yr: 3. Sheet L: 750.00 ns:0.0600 p2yr: 3. 0.69 cfs VOL: 0.32 Ac-ft TIME: IMP 0.39 Acres 78.82 10.54 min s:0.0500 s:0.1500 50 s:0.0500 50 s:0.1500 480 min BASIN ID: 10yr SBUH METHODOLOGY TOTAL AREA ....... : RAINFALL TYPE .... : PRECIPITATION .... : TIME INTERVAL .... : NAME: 10 year pre construction 1.00 Acres BASEFLOWS: 0.00 cfs TYPE1A PERV 5.00 inches AREA..: 1.00 Acres 10.00 min CN .... : 42.00 TC .... : 182.50 min 0.20 200.00 ns:0.800 ABSTRACTION COEFF: TcReach - Sheet L: 0 p2yr: TcReach - Sheet L:1500.00 ns:0.8000 p2yr: 3.50 PEAK RATE: 0.03 cfs VOL: 0.03 Ac-ft TIME: 3.50 s:0.0500 s:0.1500 1330 min IMP 0.00 Acres 0.00 0.00 min 11/4/01 11:25:30 am Shareware Release DRAINAGE AND EROSION CONTROL PLAN RESIDENTIAL LOT FOR: RON & MONIKA SHEPARD page 2 BASIN SUMMARY BASIN ID: 10yr+ SBUH METHODOLOGY TOTAL AREA ....... : RAINFALL TYPE .... : PRECIPITATION .... : TIME INTERVAL .... : NAME: 10 year 1.00 Acres TYPE1A 5.00 inches 10.00 min ABSTRACTION COEFF: 0.20 TcReach - Sheet L: 200.00 ns:0.150 TcReach - Sheet L:1500.00 ns:0.060 impTcReach - Sheet L: 50.00 ns:0. impTcReach - PEAK RATE: post construction BASEFLOWS: 0.00 cfs PERV AREA..: 0.61 Acres CN .... : 68.00 TC .... : 28.85 min Sheet L: 0.37 cfs 0 p2yr: 3.50 s:0.0500 0 p2yr: 3.50 s:0.1500 0110 p2yr: 3.50 s:0.0500 750.00 ns:0.0600 p2yr: 3.50 s:0.1500 VOL: 0.19 Ac-ft TIME: 480 min BASIN ID: 2yr SBUH METHODOLOGY TOTAL AREA ....... : RAINFALL TYPE .... : PRECIPITATION .... : TIME INTERVAL .... : ABSTRACTION COEFF: TcReach - Sheet TcReach - Sheet PEAK RATE: NAME: 2 year pre construction 1.00 Acres TYPE1A 3.50 inches 10.00 min 0.20 BASEFLOWS: AREA..: CN .... : TC .... : L: 200.00 ns:0.8000 p2yr: L:1500.00 ns:0.8000 p2yr: 0.01 cfs VOL: 0.00 cfs PERV 1.00 Acres 42.00 182.50 min 0.00 Ac-ft 3.50 s:0.0500 3.50 s:0.1500 TIME: 1440 min BASIN ID: 2yr+ SBU}{ METHODOLOGY TOTAL AREA ....... : RAINFALL TYPE .... : PRECIPITATION .... : TIME INTERVAL .... : NAME: 2 year post construction 1.00 Acres TYPE1A 3.50 inches 10.00 min BASEFLOWS: 0.00 cfs PERV AREA..: 0.61 Acres CN .... : 68.00 TC .... : 28.85 min ABSTRACTION COEFF: 0.20 TcReach - Sheet L: 200.00 ns:0.1500 p2yr: 3.50 s:0.0500 TcReach - Sheet L:1500.00 ns:0.0600 p2yr: 3.50 s:0.1500 impTcReach - Sheet L: 50.00 ns:0.0110 p2yr: 3.50 s:0.0500 impTcReach - Sheet L: 750.00 ns:0.0600 p2yr: 3.50 s:0.1500 PEAK RATE: 0.16 cfs VOL: 0.10 Ac-ft TIME: 480 min IMP 0.39 Acres 78.82 10.54 min IMP 0.00 Acres 0.00 0.00 min IMP 0.39 Acres 78.82 10.54 min 11/4/01 11:25:30 am Shareware Release DRAINAGE AND EROSION CONTROL PLAN RESIDENTIAL LOT FOR: RON & MONIKA SHEPARD page HYDROGRAPH SUMMARY PEAK TIME VOLUME HYD RUNOFF OF OF Contrib NUM RATE PEAK HYDRO Area cfs min. cf~AcFt Acres 1 0.005 1440 136 cf 1.00 2 0.026 1330 1133 cf 1.00 3 0.065 1320 3613 cf 1.00 4 0.159 480 4195 cf 1.00 5 0.368 480 8105 cf 1.00 6 0.693 480 14013 cf 1.00 10 0.132 510 4195 cf 1.00 11 0.240, 530 8105 cf 1.00 12 0.435 530 14013 cf 1.00 11/4/01 11:25:31 am Shareware Release DRAINAGE AND EROSION CONTROL PLAN RESIDENTIAL LOT FOR: RON & MONIKA SHEPARD page STORAGE STRUCTURE LIST TRAPEZOIDAL BASIN Description: DRYWELL Length: 182.00 ft. Side Slope 1: 0 Side Slope 2: 0 Infiltration Rate: ID No. Ti Width: 2.00 ft. Side Slope 3: 0 Side Slope 4: 0 4.56 min/inch 11/4/01 11:25:31 am Shareware Release DRAINAGE AND EROSION CONTROL PLAN RESIDENTIAL LOT FOR: RON & MONIKA SHEPARD page DISCHARGE STRUCTURE LIST RISER DISCHARGE Description: RISER Riser Diameter (in): Weir Coefficient...: Orif Coefficient...: ID No. RI 6.00 elev: 103.00 ft 9.739 height: 104.00 ft 3.782 increm: 0.10 ft