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Home My WebLink AboutWPO200400007 Calculations 2004-02-11 New Nowt TEMPORARY SEDIMENT BASIN PROJECT Hollymead Town Center PROJ NO. 1132 BASIN # SEDIMENT BASIN DATE 4/1/2004 LOCATION SWM #3 BY JDB INPUT DRAINAGE AREA 46.10 ac BASIN VOLUME DESIGN WET STORAGE 1. MINIMUM REQUIRED VOLUME 3088.70 cy 2. AVAILABLE BASIN VOLUME AVFRAGF FNf) ARFA - BASIN VOl I lME FSTIMATFS ELEVATION AREA VOLUME ` VOLUME TOTAL ft sf cf I cy cy 471 20,260.00 21,815.00 807.96 472 23,370.00 807.96 54,174.00 2,006.44 474 30,804.00 2,814.41 68,909.00 2,552.19 476 38,105.00 5,366.59 91,491.00 3,388.56 478 45,632.00 8,755.15 99,018.00 3,667.33 480 53,386.00 12,422.48 114,752.00 4,250.07 482 61,366.00 16,672.56 130,942.00 4,849.70 484 68,576.00 21,522.26 147,581.00 5,465.96 486 78,005.00 26,988.22 REQUIRED WET STORAGE VOLUME 3,088.70 cy APPROX. ELEVATION 474.01 3. EXCAVATE CUBIC YARDS 4. AVAILABLE VOLUME BEFORE CLEANOUT REQUIRED 1544.35 cy 5. ELEVATION CORRESPONDING TO CLEANOUT LEVEL 472.97 6. DISTANCE FROM DEWATERING ORIFICE TO C/O LEVEL INVERT DEWATERING ORIFICE R'QD 474.01 INVERT DEWATERING ORIFICE USED 478.50 APPROX. VOLUME AT INVERT USED 9679.54 cy DISTANCE FROM INVERT TO C/O LEVEL 5.53 ft DISTANCE ACCEPTABLE WET STORAGE VOLUME ACCEPTABLE DRY STORAGE 7. MINIMUM REQUIRED VOLUME 3088.70 cy 8. TOTAL AVAILABLE VOLUME AT CREST OF RISER CREST OF RISER 484.00 APPROX. AVAILABLE TOTAL VOLUME 17701.23 cy ADEQUATE DRY STORAGE VOLUME 9. DIAMETER OF DEWATERING ORIFICE 0 10.03 cfs d(1ST ITERATION) 15.18 in d(2nd ITERATION) 16.20 in d(3rd ITERATION) 16.29 in d(4th ITERATION) 16.29 in USE d 24 In 10. DIAMETER OF FLEXIBLE TUBING 26 in NOT A STANDARD SIZE Page 1 SWM3 Sediment Basin.xls TEMPORARY SEDIMENT BASIN PROJECT Hollymead Town Center PROJ NO. 1132 BASIN # SEDIMENT BASIN DATE 4/1/2004 LOCATION SWM #3 BY JDB PRELIMINARY DESIGN 11. PRELIMINARY DESIGN ELEVATIONS: CREST OF RISER 484.00 It 1 TOP OF DAM 486.90 ft DESIGN HIGH WATER 478.50 ft _ UPSTREAM TOE OF DAM 475.00 ft BASIN SHAPE 12. LENGTH OF FLOW / EFFECTIVE WIDTH: SURFACE AREA OF NORMAL POOL 47570 sf LENGTH OF FLOW PATH 290 ft EFFECTIVE WIDTH 164 ft LIWe 1.77 BAFFLES REOUIRED RUNOFF (RATIONAL METHOD CALCULATION) USE MAXIMUM C VALUE DURING CONSTRUCTION AND MINIMUM Tc VALUE 13. FLOW FROM 2 -YEAR STORM C: 0.50 Tc: 5.0 I: 5.5 in/hr 0= 126.8 cfs 14. FLOW FROM 25 -YEAR STORM C: 0.50 Tc: 5.0 I: 8.1 in/hr Q= 186.7 cfs PRINCIPAL SPILLWAY DESIGN 15. REQUIRED SPILLWAY CAPACITY: EMERGENCY SPILLWAY? (Y /N) N REQUIRED SPILLWAY CAPACITY: 186.7 CFS 16. ASSUMED AVAILABLE HEAD: ELEV. OF CREST OF E.S. IF USED: 485.00 ASSUMED AVAILABLE HEAD= -5.50 ft 17. RISER DIMENSIONS: 1 RISER DIAMETER: 72.00 in (From Plate 3.14 -8 or Calcs) ACTUAL MAX. ELEV.: 478.50 ft (From Calcs if appropriate) ACTUAL HEAD: -5.50 ft (From Plate 3.14 -8 or Cates) 18. BARREL LENGTH: 1 BARREL LENGTH: 100.00 ft BARREL INVERT OUT: 475.00 ft HEAD H ON BARREL: 3.50 ft (From Plate 3.14 -7) 19. BARREL DIAMETER: BARREL DIAMETER: 48 in (From Plate 3.14A or 3.148) 20. TRASH RACK AND ANTI - VORTEX DEVICE: DIAMETER: 102 in (From Plate 3.14D) HEIGHT: 36 in EMERGENCY SPILLWAY DESIGN 21. REQUIRED SPILLWAY CAPACITY: Qe = 0(25) -Qp = N/A CFS 22. DIMENSIONS: BOTTOM WIDTH (b): 10.00 ft (From Table 3.14 -C) SLOPE OF EXIT CHANNEL (s): 2.60 ft/ft (From Table 3.14 -C) MIN. LENGTH EXIT CHANNEL (x): 70.00 ft (From Table 3.14 -C) FINAL DESIGN ELEVATIONS 25. ELEVATIONS: TOP OF DAM: 486.90 ft DESIGN HIGH WATER: 478.50 ft EMERGENCY SPILLWAY CREST: N/A ft PRINCIPAL SPILLWAY CREST: 484.00 ft DEWATERING ORIFICE INVERT: 478.50 ft CLEANOUT ELEVATION: 472.97 ft Page 2 SWM3 Sediment Basin.xls New NW' Hollymead Town Center Regional Service area `B" Max Greene March 17, 2004 The submittal dated March 12, 2004 is not a complete package. Official E &SC review is not possible without the narrative. Please refer to VESCH. Please note: "Areas of disturbance must include all previous /currently disturbed areas. When the E &SC plan and Narrative are approved the Rough Grading permit for the entire site will become null and void." The following comments are cursory and not complete due to the lack of required information. Plan sheet: 1. The proposed disturbed area doesn't match the current site conditions. Much more of the site is currently disturbed than is depicted on this submittal. 2. Proposed sediment basin #3 computations do not include the disturbed area above the proposed cleanwater diversions. The basin shall be designed to capture the entire drainage area, pre -, during or post- development (whatever's the larger). 3. The proposed cleanwater diversions shall be removed from E &SC plan sheet. They are shown through the current disturbed area. 4. Plan sheet match lines for sheet ES3 are incorrect. Both match line references refer to the same sheet ES3. 5. Match lines are not correct. When the sheets are cut and pasted together they overlap significantly. Please correct the E &SC plans match lines. 6. The variance request for 3.5 -acre sediment traps is denied. The site conditions appear to allow for substantially smaller sediment traps in order to remove the existing sediment basins. 7. E &SC plan submittal appears to require more phasing sheets to clarify how the site progression shall proceed within all local, State and federal laws.