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HomeMy WebLinkAboutDrainage Reports - 10/23/2003 (4)June 20, 2003 ' Revised August 20, 2003 1 Mr. Wes Lamarque City of Fort Collins Storm Water Utility 700 Wood Street Fort Collins, CO 80522 Re: Pioneer Charter School — Storm Drainage Report CO-03-03-1 Dear Wes, Please accept the following revised letter report on behalf of the Pioneer Charter School to ' demonstrate the site's compliance with the previously approved Final Drainage Reports for Rigden Farm Filing One and Filing Six, as prepared by JR Engineering. ' INTRODUCTION This site is legally known as Tract E of Rigden Farm Filing One. It contains 4.27 acres and is bounded on all four sides by existing city roadways, namely being Custer Drive, Kansas Drive, Limon Drive and Minnesota Drive. The site is bisected by a previously constructed storm drainage channel/detention pond which is referred to as Pond 217. The design for this pond was ' included as part of the Filing One Drainage Report and was constructed with that Filing. The original stage -storage table is attached for reference. There are three ponds in series which drain from west to east (Ponds 216, 217 and 218) which were modeled using EXTRAN and SVRAM. All detention and water quality requirements for this site have been met by the overall Ridgen Farm development. Rigden Farm Filing Six updated the basins in the vicinity of this pond based upon anticipated ultimate development; however, the original pond sizing (stage -storage) was not altered. Filing Six did update the SWMM model using the updated basin information; however, the EXTRAN model was not re -run with that Filing. Excerpts from the Filing Six report are attached for reference. The Filing Six updated SWMM model shows that the peak storage of Pond 217 during a 100- year storm event is 2.2 acre-feet. By interpolating from the original stage -storage curve, it was determined that the new 100-year water surface elevation for the pond during ultimate 1 development is 4924.0. This was discussed previously with Basil Hamdan. We have shown a 30-foot wide emergency spillway into the parking lot at elevation 4924.3 by turning down the proposed 6-inch curb, and a minimum top of pond elevation of 4925.0 in order to comply with 1 minimum freeboard criteria. 1235 HONEYSUCKLE CT. • WINDSOR, CO 80550 TEL. 970.222.9133 • FAX. 970.686.9576 I Mr. Wes Lamarque Revised August 20, 2003 Page 2 of 4 EXISTING CONDITIONS The site is currently vacant and contains a high stand of grasses. A drainage channel/ pond exists through the middle of the site as do the inlet and outlet culverts. The eastern (lower) end of the pond was over excavated with the Filing One construction to serve as a temporary sediment 1 basin. This basin will continue to function during the proposed construction. The site drains in three distinct directions and these general basin lines have been maintained with the proposed development and in conformance with the Ultimate Development basin delineations as shown in the Rigden Farm Filing Six Final Drainage Report. PROPOSED DEVELOPMENT Portions of the existing pond are to be re -graded with this development. The northwest corner of the pond has been re -graded in order to contain the 100-year WSEL within the recorded Drainage Easement. The southwest corner has been re -graded to incorporate a small amphitheatre into the embankment. A proposed Drainage Easement is shown for this area to contain the 100-year WSEL. The southeast corner of the pond has been steepened to a 3:1 slope, in accordance with the previously approved variance made part of the Filing One Final Drainage Report, in order to accommodate the proposed improvements adjacent to the pond Attached are the previously approved stage -storage calculations and the calculations with the proposed improvements. At each critical stage the storage is shown to be equal to or greater than the previously approved design. Therefore, we request that the pond volume be deemed in substantial conformance with the approved design. A pedestrian bridge is proposed to cross the drainage channel/pond. The bottom chord of the bridge is to be set at a minimum elevation of 4924.0 in order to free span the proposed 100-year WSEL. While the abutments will reduce the overall width of the channel the pond functions in a backwater condition; therefore, the constraint will not impact the function of the pond. BASIN DESCRIPTIONS The site is divided into three basins, the southern (Basin 1), the middle (Basin 2) and the northern (Basin 3). Basin 1 is comprised of the southern half of the school building and the entire parking area south of the channel. This basin drains to the south toward Custer Drive where it is intercepted and conveyed via curb, gutter and storm drainage pipes to the Water Quality ponds located north of the Foothills Regional Channel. Portions of this basin sheet flow over the existing Custer Drive sidewalk in accordance with the LCUASS. The remaining concentrated areas are conveyed under the sidewalk via proposed channels and/or sidewalk chases to the flow line of Custer Drive. 1 '1 Mr. Wes Lamarque Revised August 20, 2003 Page 3 of 4 Basin 2 is comprised mainly of the existing drainage channel, or Pond 217. The northern half of the proposed school building and a small area north of the channel will also drain into this basin. Pond 217 discharges to the east under Minnesota Drive via an existing storm culvert and into Extended Detention (Water Quality) Pond 218 prior to being released into the Foothills Regional Channel. Basin 3 drains to the north via sheet flow toward Limon Drive and runoff is conveyed in the existing storm drainage system to pond 218 which is just east of this site. This basin is proposed to remain undisturbed; however, this area has the potential to be developed in the future with additional parking and another building. Therefore, the runoff calculations provided have assumed this ultimate development. A note on the Utility Plans requires that future development of this basin requires review by the affected city agencies. Filing Six similarly utilized an "Ultimate Development" condition for the basins that make up the School site. All the area contained within the site were assumed to be Commercial or Multi - Family with an imperviousness of 70% used for the middle basin (SWMM Sub basin 583) and 90% for both the north and south basins (SWMM Sub basins 584 and 58) for an average site imperviousness of 0.79. The actual imperviousness of the site, including the future parking and building site to the north of the channel, is 0.53, with a composite C Factor of 0.63. Therefore, it is requested that the site be deemed in substantial conformance with the previously approved Final Drainage Reports. EROSION CONTROL Erosion and sedimentation will be controlled on -site by use of silt fences, culvert inlet protection, a gravel construction entrance, the existing sediment basin and seeding and mulch. The measures are designed to limit the overall sediment yield increase due to construction as required by the City of Fort Collins. During overlot and final grading the soil will be roughened and furrowed perpendicular to the prevailing winds. During the performance of the work required by these specifications or any operations appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the contractor shall furnish all labor, equipment, materials, and means required. The Contractor shall carry out proper efficient measures wherever and as necessary to reduce dust nuisance, and to prevent dust nuisance that has originated from his operations from damaging crops, orchards, cultivated fields, and dwellings, or causing naissance to persons. The Contractor will be held liable for any damage resulting from dust originating from his operations under these specifications on right- of-way or elsewhere. It is unlawful to track or cause to be tracked mud or other debris onto city streets or rights -of - way unless so approved by the Director of Engineering in writing. Wherever construction vehicles access routes or intersect paved public roads, previsions must be made to minimize the transport of sediment by runoff or vehicles tracking onto the paved surface. Stabilized construction entrances are required with base material consisting of 6" coarse aggregate. The contractor will be responsible for clearing mud tracked onto city streets on a daily basis. Mr. Wes Lamarque Revised August 20, 2003 Page 4 of 4 All temporary and permanent erosion and sediment control practices must be maintained and repaired as needed to assure continued performance of their intended function. Silt fence will require periodic replacement. The existing sediment trap located at the east end of the drainage channel shall remain during the construction period of this project and shall be cleaned when accumulated sediments equal approximately one-half of trap storage capacity. Maintenance is the responsibility of the contractor. All disturbed areas must be seeded and mulched within 30 days of project start. Vegetation shall not be considered established until a ground cover is achieved which is demonstrated to be mature enough to control soil erosion to the satisfaction of the City Inspector and to survive severe weather condition. I trust that I have been able to address your concerns. If you have any questions or comments please contact me at (970) 222-9133. Sincerely, oQ,PDO RS%S Uov : t At�y/�.:F-per crr �� , O 33441 Robert Almirall, P.E. per Colorado Professional Engineer 33441 0 �s9/ONALEN�\� Attachments APPENDIX PREVIOUS REPORT EXCERPTS, DRAINAGE AND EROSION CONTROL CALCULATIONS K = headloss coefficient V = average velocity (ft/s) g = gravitational constant (32.2 ft/sz) The storm pipe design was performed for the ultimate build -out of Rigden II in all three parcels and is included in Appendix E of this report. 5. REGIONAL HYDROLOGY 5.1 Methods and Approach The hydrology for Rigden II, as in the O.D.P., was evaluated using an integrated UDS WMM2PC, MODSWMM. The original Master Plan SWMM model was developed by Resource Consultants Inc. in 1981. An updated Master Plan model was completed by Faucett Engineering in 1997 using the then -current 100-year rainfall depth (2.89" of rain for the 100-year, 2-hour storm). An update to the Master Plan SWMM model was completed by Anderson Consulting Engineers, Inc. (ACE) in July 1999. The "Overall Drainage Report for the Rigden Farm O.D.P." (Feb. 1999) was developed concurently with the ACE model and includes Rigden Farms ultimate conditions. The Rigden O.D.P. model was used as abasis for the SWMM model for this study because it incorporates the most up to date information for the Foothills Basin and Rigden Farm. 5.2 Development of SWMM Model The SWMM model for Rigden II revises the basin parameters to match the proposed improvements. Minor changes were made to sub -basins 58, 65, 66, 67, 68, 69,581, 582, 584, and 681 of the Rigden O.D.P. model. Sub -basins 671, 691, and 682 were added. The conceptual storage -discharge rating curve for Detention Pond 216 was modified to reflect proposed grading and Detention Pond 269 was added in Basin 69. The total basin area for Rigden Farm in the Rigden II model is 315.9 acres, 0.7 acres less than the Filing One model. This difference is due to changes in basin boundaries along Drake Road and Timberline Road. A copy of the SWMM Model Sub -basin Delineation is included in Appendix F of this report. Drainage and Erosion Control Report Rigden Farm — Filing Six Page 17 December 5, 2001 I 1 � 1 1 The values recommended by the City of Fort Collins were used for the percent imperviousness. These values were also close to the estimated values for the Rigden Farm development. For commercial areas, a percent impervious value of 90% was used and for multifamily areas, 70% of the area was assumed impervious. For single family residential sub -basins, 45% of the area was assumed impervious. Basin widths were calculated based on an average overland flow path length that varies according to land use. For undeveloped basins, the overland flow path is estimated to be between 100 ft and 500 ft depending on the topography. For developed basins, the overland flow path is estimated to be between 50 to 300 ft. The following table summarizes the basin parameters for the Rigden H model. Table 5.1 - SWMM Suhhasin Paramatarc fnr 111fi-1n ne.,e1.,r...,. # SWMM Subbasin Basin Width W (if) Area (ac.) Overland flow Path, L (ft) % Impervious Slope (%) Basin Description 58 1.0% 6000 41.1 298 90% Commercial 581 3450 22.4 283 90% 0.8% Commercial 582 1700 11.5 295 80% 2.0% Multi -family & Commercial 583 400 2.5 267 70% 2.0% Multi -family 584 2900 _ 19.7 _ _2_96 _ 90% 1.5% _ Dense mule -family & commercial 65 1200 4.0 145 10% 3.0% Adjacent to Regional Channel 66 4900 15.1 134 12% 2.0% Adjacent to Regional Channel 67 10400 99.2 415 45% 2.0% Single Family 671 2300 8.3 157 19% 10.0% Adjacent to FCRID 68 2400 25.2 457 45% 2.0% Single Family 681 640 6.0 408 45% 1.5% Single Family 682 500 3.5 305 45% 1.5% Single Family 69 5800 53.5 402 45% 1.9% Sin le Famil 691 1 1700 1 3.9 1 100 31% 10.00/6 Adjacent to FCRID ' 5.3 Pond Description Six ponds will be provided for Rigden II. Two primary water quality/detention ponds will be located in the northeast and southeast comers of the site. Three water quality ponds will be located south of the Foothills Regional Channel. A detention pond will be located in the Northwest Roads area. 1 1 Water quality/detention Pond 216 will be north and east of the improved Drake and Ziegler Roads and water quality/detention Pond 269 will be south of Rigden Parkway and west of Ziegler Road. Both Ponds 216 and 269 will be large wet ponds with detention volume available above the permanent water surface elevation. The detention ponds will have water Drainage and Erosion Control Report Page 18 Rigden Farm — Filing Six December 5, 2001 I 1 1 97:1 133.0 1.5 2 44. 98:4 90.0 .6 0 36. 102:2 5.5 .1 20.3:0 4 14. 104:2 5.1 .1 .9:0 1 10. 109:2 132.8 .1 3.0:D 0 43. 115:3 429.9 (DIRECT FLOW) 0 48. 116:1 347.5 4.9 1 S. 129:5 320.8 5.3 0 37. 133:5 178.9 3.2 0 38. 134:4 906.2 5.9 0 38. 142:1 455.0 4.7 2 14. 144:1 114.9 .9 1 1. 1S0:2 5.1 1.0 1 12. 152:5 78.2 3.5 0 37. 153:5 6.8 1.4 4 32. 154:5 5.5 1.4 4 19. 156:5 57.7 1.8 0 44. 157:2 428.0 .1 3.3:D 3 35. 159:2 B.4 .1 2.7:D 2 2. 162:3 182.6 (DIRECT FLOW) 0 36. 163:4 109.8 1.0 0 51. 172:2 58.8 .1 6.6:D 1 16. 173:5 53.2 4.1 1 29. 178:4 537.0 4.1 0 51. 184:5 173.3 4.9 0 40. 185:1 84.6 2.0 2 30. 188:1 870.3 3.0 0 46. 193:2 73.3 .1 12.6:D 1 32. 194:1 922.8 7.1 0 55. 201:2 22.9 .1 1.1:D 0 44. 207:2 20.0 .1 9.7:D 2 14. 208:2 20.0 .1 9.5:D 2 6. 209:2 9.0 .1 5.5:0 2 15. 210:2 25.4 .1 1.2:D 0 50. 211:2 9.9 .1 3.1:D 2 3. 212:2 40.3 .1 .8:D 0 42. 213:2 - .2 .1 11.4:D 2 1. 214:2 23.3 .1 11.5:D 2 10. 215:2 8S.1 .1 33.2:D 2 19. 216:2 134.0 .1 28.7:D 2 27. 217:2 19.7 .1 2.2:D 218:2 109.5 .1 1.6:D 0 39. 244:2 6.0 .8 2 18. 251:2 5.4 .1 .6:D 1 27. 257:1 463.1 3.7 3 33. 269:2 129.7 .1 4.4:0 0 47. 273.3 88.8 (DIRECT FLOW) 0 51. 288:3 922.9 (DIRECT FLM 0 41. 303:2 5.6 .1 1.4:D 1 55. 306:2 35.2 .1 .2:D 0 36. 307:5 31.5 2.0 0 39. 313:2 1.7 .1 .6:D 1 37. 338:2 64.1 .1 5.6:D 1 16. 351:3 315.3 (DIRECT FLOW) 0 36. 361:4 315.3 1.0 0 36. 400:4 60.5 .6 0 40. 401:4 132.5 .8 0 41. 410:2 2.8 .1 2.9:D 2 15. 413:2 1.5 .1 1.9:D 2 7. 444:3 127.1 WIFE= FLOW) 0 55. 466:3 617.2 (DIRECT FLLW) 0 40. 471:3 248.0 (DIRECT FLOW) 0 38. S00:3 1118.2 (DINT FLOW) 0 59. 544:3 6.0 (DIRECT FUW) 2 14. 562:3 30.0 (DIRECT FLCW) 0 29. 600:4 327.0 1.3 0 36. 644:3 121.1 (DIRECT FLM 0 55. 662.3 152.6 (DIRECT FUYA) 0 36. 849:3 14.2 (DIREST FT-M 0 16. 916:3 S28.3 (DIRECT FLOW) 0 41. Rigden Farm- Filing Six SWMM output File: 9164-PRO.out, 09/17/01 Page 21 of 22 _ ... NORTH TRI. 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Rigden Farm Pond 217 Proposed Detention Pond - Stage/Storage As Proposed June 16, 2003 LOCATION: PIONEER SCHOOL PROJECT NO: CO-03-03-1 COMPUTATIONS BY: R. ALMIRALL SUBMITTED BY: INTERWEST CONSULTING GROUP DATE: 6/ 16/2003 V = 1/3 d ( A + B + sgrt(A`B)) where V = volume between contours, ft3 d = depth between contours, ft A = surface area of contour 100-yr WSEL top of berm - POND 217 Stage (ft) Surface Area Incremental Storage (ac-ft) Total Storage (ac-ft) 4917.25 0 4918.00 5850 0.03 0.03 4919.00 9352 0.17 0.21 4920.00 12637 0.25 0.46 4921.00 15486 0.32 0.78 4922.00 19014 0.40 1.18 4923.00 22786 0.48 1.65 4924.00 25666 0.56 2.21 4925.00 Proposed Pond Volume RUNOFF COEFFICIENTS & % IMPERVIOUS LOCATION: Pioneer Charter School PROJECT NO: CO-03-03-1 COMPUTATIONS BY: R. Almirall DATE: 812012003 Recommended Runoff Coefficients from Table 3-3 of City of Fort Collins Design Criteria Recommended % Impervious from Urban Storm Drainage Criteria Manual Runoff 0/0 coefficient Impervious Strei SUBBASIN DESIGNATION TOTAL AREA (ac ) 1 1.59 2 1 79 3 1 34 Total 4.72 Equations - Calculated C coefficients C=Z(Ci Cval and Imperviousness Interwest Consulting Group Cl) 0 C14 0 \ � 7 � � < \_ 2 \ 3 \ 2 / z / S \ \ en r4 o R \ \ 1.6 j \ $ / & 3 / - � 0 c _ Q eq ¥ � < � \ � � � _ S ) / w 3 2 - / ] C, n / \ \ \ \ k ƒ \ \]\ � � Q « & �5z ƒ\$ e @ { \ © \ � k \\ cc 0 &< Asa cc/ \ 3 & \ cz � § { k & § $ \ ca ( E.\ 2 @ cn z > > < < _ a ) / § / ƒ f : k \ E / CL / \ E k _ s I PAGE ?3 1 I f� �i I O I O- O,% O O C I O v , ctntnt.n to I co co q q co I 1 I C I Ql ON c7N C C C O C C I C I "Cr vc,Zr tntnLr.tntntn 1 c I C CC CO CC 00 CC (^ CO q CO I 1 1 C I ccclON mCT.CTCN011O�01.01G1COC 1 c I ccC-cvvcccccctntntr. 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N N N .-r am r+ r-+ 0 0 = 1 0 O O O C O O O O O C O 0 0 C) 0 0 0 0 C) 0 0 0 0 O C-0 F- I O O C O O O C O O O O O O O O O O O O O O O C O 0 0 JZLL 1 Ncn-=-Ln1.0r� W (7)CD C')cLntDr�CJG1Ou")OLnCCLnCD L.t_ liJ N N M en Lt') N TABLE S.1 Interwest Consulting Group 8/19/2003 EFFECTIVENESS CALCULATIONS PROJECT: PRESTON 3RD STANDARD FORM B COMPLETED BY: ALR DATE: 19-Aug-03 EROSION CONTROL C-FACTOR P-FACTOR METHOD VALUE VALUE COMMENT BARE SOIL 1.00 1.00 SMOOTH CONDITION ROUGHENED GROUND 1.00 0.90 ROADS/WALKS 0.01 1.00 GRAVEL FILTERS 1.00 0.80 PLACED AT INLETS SILT FENCE 1.00 0.50 SEDIMENT TRAP 1.00 0.50 STRAW MULCH (S = 1-5%) 0.06 1.00 FROM TABLE 8B STRAW BARRIERS 1.00 0.80 EFF = (1-C* P)* 100 MAJOR SUB BASIN AREA EROSION CONTROL METHODS BASIN BASIN (Ac) I 1.59 ROADS/WALKS 0.94 Ac. ROUGHENED GR. 0.40 Ac- STRAW/MULCH 0.25 Ac. SILT FENCE NET C-FACTOR 0.27 NET P-FACTOR 0.49 EFF = (I-C*P)* 100 = 87.0% 2 1.79 ROADS/WALKS 0.39 Ac. ROUGHENED GR. 0.30 Ac. STRAW/MULCH 0.80 Ac. GRAVEL FILTER NET C-FACTOR 0.20 NET P-FACTOR 0.65 EFF = (I-C*P)* 100 = 87.2% 3 1.34 ROADSIWALKS 0.08 Ac. NET C-FACTOR 0.00 NET P-FACTOR 0.06 EFF = (I-C*P)* 100 = 100.0% TOTAL AREA = 4.72 Ac TOTAL EFF = 90.8% ( E (basin area * eff) / total area REQUIRED PS = 78.9% Since 90.8% > 78.9%, the proposed plan is o.k. C:\documents\pr\03\Pioneer\design\erosion control PIONEER CHARTER SCHOOL EROSION CONTROL COST ESTIMATE JOB NO. CO-03-03-1 EROSION CONTROL MEASURES COMPLETED BY: RA ITEM I DESCRIPTION UNITS I UNIT COST lQUANTITY I TOTAL COST TEMPORARY SEED & MULCH ACRE $ 655.00 1.86 $ 1,218.30 2 SILT FENCE LF $ 3.00 525 $ 1,575.00 3 GRAVEL CONSTRUCTION ENTRANCE EACH $ 550.00 1 $ 550.00 4 INLET PROTECTION EACH $ 150.00 1 $ 150.00 COST $ 3,493.30 CITY RESEEDING COST FOR TOTAL SITE AREA ITEM DESCRIPTION UNITS I UNIT COST IQUANTITY I TOTAL COST 1 RESEED/MULCH ACRE S 655.00 4.27 $ 2,796.85 COST $ 2,796.85 SECURITY DEPOSIT $ 3,493.30 REQUIRED EROSION CONTROL SECURITY DEPOSIT WITH FACTOR OF 150% $ 5,239.95