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Home My WebLink AboutCT 08-07; TEMPORARY DESILTING BASIN REPORT; 2011-12-27LA COSTA TOWN SQUARRE ED i4AR3o2o12 LAND LVELOpMENT CT 08-07 ENGINEERING TEMPORARY DESILTING BASIN REPORT JOB NO. 101290 December 27, 2011 Prepared For: PROPERTY DEVELOPMENT CENTERS 5918 Stoneridge Mall Road Pleasanton, CA 94588 (925)738-1232 Prepared by: O'DAY CONSULTANTS, INC. A. 2710 Loker Avenue West Suite 100 C 7003 r% ((( Carlsbad, California 92008-6603 Tel: (760) 931-7700 EXP Fax: (760)931-8680 FC ! Nichole A. Fine RCE 70035 DATE EXP. 09/30/12 Temporary Desilting Basin Calculations Desilting Basin Sizing Desilting basins were sized based on the 10-year, 6-hour storm event. The design particle size used is .01 mm. (fine silt) The equation used to size the basins is: As= 1.2*Qavg/ Vs Qavg C*Iavg*A C= 0.35 Iavg=1.8"I6 hr = 0.30 in/hr 10-year, 6-hour storm event= 1.8" A= area of basin Vs= 0.00024 ft's (.01mm sized particle) where As is the appropriate surface area for trapping particles of a certain size and Vs is the settling velocity for that size particle. In this case, Vs= .00024 ft/s. Qavg is the average runoff from each basin during a 10-year, 6-hour storm. Temporary Desiltation Basin Capacity per DS-3 Desiltation basin sizes were also checked per the capacity table in the City of Carlsbad Standard Drawing DS-3. All of the basins' capacity is significantly greater than that required by DS-3. Sediment Storage Volume Required The amount of sediment that the temporary desilting basins are designed to store is the amount generated by 5 years worth of 2-year, 24-hour storm events. The two-year storm event was used per City standards. (Chapter 7-Grading and Erosion Control Standards) The universal soil loss equation was used to estimate sediment volumes entering the desilting basins. A= R x K x LS x C x P A= soil loss, tons/(acre)(year) R= rainfall erosion index, 100 ft. tons/acre x in/hr K= soil erodibility factor, tons/acre per unit of R LS= slope length and steepness factor, dimensionless P= erosion control practice factor, dimensionless Rainfall Erosion Index, R For a Type I Storm: R=16.55 p22 = 16.55*(1.3)22 = 29.48 P=1.3" (2-year, 6-hour storm event) Soil Erosion Factor K Values for the Soil Erosion Factor, K, were determined from the USDA Natural Resources Conservation Service (NRCS) Web Soil Survey. There are three soil types identified on site, the value's for K are as follows: K Factor, Rock Free— Summary by Map Unit.— San Diego County Area, California (CA638) Map unit symbol Map unit name Rating Acres in AOl Percent of AOl AtE Mornont cisy, 15 to 30 percent .20 3.6 48.3% I-rD2 Huerhuerotoam, 9 to 15 percent opes. ended .37 3.8 50.6% SnG San Miguel-Exchequer rocky sift toams, 9 to 70 percent slopes .64 Totals for Area of Interest 7,5 100.0% See attached for a map of each soil type. Slope Length and Steepness Factor LS See attached Table 5.5 taken from Erosion Control Handbook for LS equation used. Cover Factor C Graded Pad: C=1.0 Erosion Control Practice Factor P Pads will be compacted and smooth (P = 1.3) Dewatering Orifice Sizing Calculations The dewatering holes on the standpipes for each basin are designed to allow sediment to settle for 40 hours before outletting through the standpipe. The following equation was used to size the dewatering holes. Ao= As (2h)5 / 3600*T*Cd*(g)5 Ao= Surface area of orifice (sO As= Basin area (sO h= Head of water (ft) T= Time (hrs) Cd= 0.6 (sharp edged orifice) g= Acceleration of gravity= 32.2 ft/s2 Standpipe Riser Sizing Calculations The standpipe risers are sized to allow the 100-year storm event to outlet from the basin without completely filling it. The following equation was used to size the standpipe risers: Ao= Q/ Cd*(2gh)5 Ao= Surface area of orifice (sO Q= 100-year flow entering basin h= Head of water (ft) Cd 0.67 (sharp edged orifice) g= Acceleration of gravity= 32.2 ft/s2 I I I - Temporary Desilting Basin Calculations 10-Year Storm Event P0 = 1.8 in Basin Area (ac.) C L0 (in/hr) 1 1.56 0.35 0.3 2 2.33 0.35 0.3 3 0.91 0.35 0.3 As= (1 .2Qavg)NS Q (cfs) Vs (ftls) As regd (sf) Width Length As used 0.16 0.00024 819 15 60 900 0.24 0.00024 1,223 20 65 - 1300 0.10 0.00024 478 1330 Storage Slope Soil Volume C P Length Gradient LS Est. Soil Loss Tons CV 1 1.3 310 2 0.29 4.11 32.07 19.32 1 1.3 475 2 0.33 2.53 29.47 17.75 1 1.3 300 10 2.37 18.17 82.65 49.78 Basin Area S K 1 1.56 29.48 0.37 2 2.33 29.48 0.2 3 0.91 29.48 0.2 Sediment Storage Volume Required 2-Year, 24-Hour Storm Event, 5 Years of Sediment Basin Soil Loss (cy/5yr) Soil Storage Depth (if) 1 19.32 0.6 2 17.75 0.4 3 49.78 1.0 The settling depth minimum is 2' which is greater than the rut Water Basin Qa (in) Area (ac.) Volume (cf) Depth (if) 1 0.11 1.56 649 0.7 2 0.17 2.33 1,448 1.1 3 0.07 0.91 221 0.2 Qa=C*Ia*A la= 2yr, 6 hour = 1.3/ 6hours= 0.22 in/hr 'olume required for 2 year storm event. Basin As (A 1 900 2 1300 3 1330 1pipe Riser Sizing Calcul 0yr.240r) (in.) Tc (min. 2.8 5 Basin Q1 (W MAX 2 6.02 111111 I.flifl Cd G (ftl"2) Ao (sf) Ao (in2) 0.7 40 0.6 32.2 0.002 0.32 Use 8- 1/4 dia. holes 1.1 40 0.6 32.2 0.004 0.57 Use 12- 1/4° dia. holes 0.2 40 0.6 32.2 0.002 0.23 Use 4- 1/4° dia. holes For Q too (inJhr.) Area (Basin 1) (AC.)T C 0100 (cfs) 7.38 2.33 0.35 6.02 0.67 1 1.12 2.24 1.69 Use 24° CMP Riser I:\001017\_Office\Stormwater\DesiltBasins.xls 33 4'52" 33'4'45" 33' 4'53" .J 4 40 - - - - - - - - - - - - - - - - - - - K Factor, Rock Free—San Diego County Area, California (La Costa Town Square - Office) N- N- a, Map Scale: 1:1,540 if printed on A size (8.5" X II") sheet N .Meters A 0 20 40 00 120 .Feet 0 50 100 200 300 USDA Natural Resniircs Web Soil Survey 12/9/2011 Conservation Service National Cooperative Soil Survey Page 1 of 3 - - - - - - - - - M - - - - M - _ - - K Factor, Rock Free—San Diego County Area, California (La Costa Town Square - Office) MAP LEGEND Area of Interest (AOl) Area of Interest (AOl) Sujib Soil Map Units Soil Ratings LI 05 LI .10 LI.15 F-1 .17 F--J.20 F-1 .24 LI .28 LI .32 .37 • .43 .49 • .55 • .64 Not rated or not available Political Features • Cities Water Features - Streams and Canals Transportation .i-i-+. Rails MAP INFORMATION Interstate Highways Map Scale: 1:1,540 if printed on A size (8.5" x 11") sheet. US Routes The soil surveys that comprise your AOl were mapped at 1:24,000. Major Roads Warning: Soil Map may not be valid at this scale. Local Roads Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for accurate map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: UTM Zone uN NAD83 This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: San Diego County Area, California Survey Area Data: Version 6, Dec 17, 2007 Date(s) aerial images were photographed: 6/7/2005 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. USDA Natural Resources Web Soil Survey 12/9/2011 AM Conservation Service National Cooperative Soil Survey Page 2 of 3 K Factor, Rock Free—San Diego County Area, California La Costa Town Square - Office K Factor, Rock Free K Factor, Rock Free— Summary by Map Unit - San Diego County Area, California (CA638) Map unit symbol Map unit name Rating Acres in AOl Percent of AOl AtE Altaniont clay, 15 to 30 percent slopes .20 3.6 48.3% I-IrD2 Huerhuero loam, 9 to 15 percent slopes, eroded .37 3.8 50.6% SnG San Miguel-Exchequer rocky silt barns, 9 to 70 percent slopes .64 0.1 1.1% Totals for Area of interest 7.5 100.0% Description Erosion factor K indicates the susceptibility of a soil to sheet and rill erosion by water. Factor K is one of six factors used in the Universal Soil Loss Equation (USIE) and the Revised Universal Soil Loss Equation (RUSLE) to predict the average annual rate of soil loss by sheet and rill erosion in tons per acre per year. The estimates are based primarily on percentage of silt, sand, and organic matter and on soil structure and saturated hydraulic conductivity (Ksat). Values of K range from 0.02 to 0.69. Other factors being equal, the higher the value, the more susceptible the soil is to sheet and rill erosion by water. 'Erosion factor Kf (rock free)' indicates the erodibility of the fine-earth fraction, or I the material less than 2 millimeters in size. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff None Specified Tie-break Rule: Higher Layer Options: Surface Layer 1 I I I I USDA Natural Resources aiiiiiiiiiiii Conservation Service Web Soil Survey National Cooperative Soil Survey 12/9/2011 Page 3 of 3 I I I I I I I I I I I) Estimating Soil Loss 5.23 TABLE 5.6 C Values for Soil Loss Equation* Soil loss I Type of cover C factor reduction, % None " 1.0 0 Native vegetation (undisturbed) 0.01 99 Temporary seedings: 90% cover, annual grasses, no mulch I 0.1 90 Wood fiber mulch, % ton/acre (1.7 t/ha), with seedt 0.5 50 Excelsior mat, jutet 0.3 70 Straw mulchf 1.5 tons/acre (3.4 t/ha), tacked down I 0.2 80 4 tons/acre (9.0 t/ha), tacked down 0.05 95 *Adapted from Refs. 11, 15, and 20 tFor slopes up to 2:1. I I if a complete cover of newly seeded annual grasses is well established before the onset of rains. In many areas, seed and wood fiber mulch are applied hydraulically shortly before the rainy season. The early rains cause the seeds to germinate, but a com- plete grass cover is not established until at least 4 weeks later. During the ger- mination and early growth period, the wood fiber mulch provides only marginal protection. A C value of 0.5 is an appropriate average representing little protec- tion initially and more thorough protection when the grass is well established. I )On bare soils mulch can provide immediate reduction in soil loss, and it per- forms better than temporary seedings in some cases. Straw mulch is more effec- tive than wood fiber mulch; it reduces loss about 80 percent (C value, 0.2) when I it is applied at the rate of 3000 lb/acre (3.4 t/ha) and tacked down. Additional reduction is obtained with 8000 lb/acre (90 t/ha) of straw, but this rate may not be cost-effective. Wood fiber mulch alone (without seed) provides very little soil loss reduction; I it primarily helps seeds to become established so that the new grass can provide the erosion control. Other products, such as jute, excelsior, and paper matting, provide an intermediate level of protection; the C value equals approximately 0.3. Test results of various mulch treatments are presented in Chap. 6. I 5.2f Erosion Control Practice Factor P I The erosion control practice factor P is defined as the ratio of soil loss with a given surface condition to soil loss with up-and-down-hill plowing. Practices that reduce the velocity of runoff and the tendency of runoff to flow directly down- slope reduce the P factor. In agricultural uses of the USLE, P is used to describe plowing and tillage practices. In construction site applications, P reflects the roughening of the soil surface by tractor treads or by rough grading, raking, or disking. I I) I I 5.24 Erosion and Sediment Control Handbook TABLE 5.7 P Factors for Construction Sites (Adapted from Ref. 15) Surface condition P value Compacted and smooth 1.3 4— Trackwalked along contour* 1.2 Trackwalked up and down slopet 0.9 Punched straw 0.9 Rough, irregular cut 0.9 Loose to 12-in (30-cm) depth 0.8 *Tread marks oriented up and down elope. tTread marks oriented parallel to contours, as in Figs. 6.9 and 6.10. P values appropriate for construction sites are listed in Table 5.7. A surface that is compacted and smoothed by grading equipment is highly sus- ceptible to sheet runoff and is assigned a P value of 1.3. Trackwalking is given a value of 1.2 if the vehicle traverses along the contour. The P value is relatively high because the depressions left by cross-slope track- ing resemble up-and-down furrows and worsen runoff conditions. Trackwalking up and down slope reduces P to 0.9. The tread marks act as slope benches; they reduce runoff velocity and trap soil particles (see Fig. 6.10). Punched straw is assigned a P value of 0.9 because the action of punching the straw into the soil roughens the surface and creates a trackwalking effect. When the soil surface is disked or otherwise loosened to a depth of 1 ft, a slightly lower P value of 0.8 may be used. This condition is unlikely to occur on a construction site because compaction, not loosening, is required when fill slopes are constructed. Clearly, changing the surface condition does not provide much direct reduc- tion in soil loss; all the P values are close to 1.0. However, roughening the soil surface is essential before seeding because it greatly increases plant establish- ment (see Chap. 6) and thus also reduces the C factor. Vegetation, mulch, slope length, and gradient have far more significant effects on the erosion process and provide greater opportunities to reduce soil loss. 5.2g Combined Effects of LS, C, and P Of the five factors in the USLE, the R, LS, and C factors have the widest range. Although R for a site is constant and K is essentially a constant, slope .length and gradient, cover, and, to a limited extent, surface condition can be manipu- lated. Slope length and vegetative cover are the most effective and easily imple- mented measures. Table 5.8 compares the effect on the soil loss estimates of varying LS, C, and P. For example, a building pad with a 1 percent slope, smooth surface, and no cover has a fractional soil loss potential. A 2:1 slope, common between terraced 5.10 Erosion and Sediment Control Handbook control practices than construction in areas with low R values. If a more precise value for R is needed, other references (10, 20, 21) that explain how to calculate R for individual storms and years from local data should be consulted. An 'isoerodent" map, prepared by Wischmeier for the USDA (20) and shown in Fig. 5.2, is used to find the R value for sites east of the Rocky Mountains (approximately 104° west longitude). R can be interpolated for points between the lines. Contact local soil conservation service offices for more detailed infor- mation on R values in areas covered by this map. West of the 104th west merid- ian, irregular topography makes use of a generalized map impractical. For the western states, R is calculated by using rainfall data. Results of investigations at Fig. 5.3 Distribution of storm types in the western United States. (4) Type II storms occur in Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, and Wyoming also. Erosion and Sediment Control Handbook 14 \Ibo __/ 7 _ C The differences in peak intensity are reflected in the coefficients of the equa- tions for the rainfall factor. Figure 5.5 is a graphical representation of the equa- tions. The equations, also shown on the curves for each individual storm type, are: R = 27p22 type II R = 16.55p22 type I R = 10.2p 2.2 type IA where p is the 2-year, 6-hr rainfall in inches. (If p is in millimeters, the equations become: R = 0.0219p22, type II; R = 0.0134 p2.2, type I; R = 0.00828p22, type IA.) The R value is rounded to the nearest whole number. When the tainfall time distribution curves (Fig. 5.4) and the corresponding R' value. equations are cm. pared, it is evident that the stronger the peak intensity of the typical storm, the- higher the rainfall erosion index. 5.12 7CC 6CC SOC 0 4CC a 300 200 100 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 p = 2-year. 6-hr rain, in I I I 25 50 75 100 o = 2-year. 6-hr rain, mm Fig. 5.5 Relations between average annual erosion index and 2-year, 6-hr rainfall in California. (14) County of San Diego Hydrology Manual a Rainfall Isopluvials 2 Year Ra&ulall Event - 6 Hours )sopiuvial (inches) 4) - Orange _ - - L.oufltyj - Riverside Coun iL.1if - J. 0 EjC1MTAS 133W i If •i-'.. $OANAeEA. ' Q OEI MAR - .. - iv - IL 6 345 ct4 +Ei4 A / - J7 I - - - - 301 - 4 Ent 33°3O * ... - H1. - t - 77 5 i t '-c 300 2 - -.- ..c DPW - T T3230' Li........:- - ....._ 3 0 3MIes 1 I I Rversu1 roLrlty - 1c;r L County of San Diego Hydrology Manual Rainfall Isopluvials — —. — - - - - - - - - - - - tJ U D County of San Diego Hydrology Manual Ruinjall Isopluvials 10 Year Rainfall Event -24 Hours Isopluvial (inches) P~,, ;,- ~,,2,, GIS -.- - - MeXc -- -- ----------------------------------------. - 323O 3230 - -3 0 3 Miles Li 0 - --- TABLE 5.5 LS Values* (10) LS values for following slope lengths 1, ft (m) LS values for following slope lengths 1, ft (m) Slope - - Slope gradient 10 20 30 40 50 60 70 80 90 100 150 200 250 300 350 400 450 500 600 700 800 900 1000 ratio s, (3.0) (6.1) (9.1) (12.2) (15.2) (18.3) (21.3) (24.4) (27.4) (305) (46) (61) (76) (91) (107) (122) (137) (152) (18:3) (213) (244) (274) (305) 0.5 0.06 0.07 0.07 0.08 0.08 0.09 0.09 0.09 0.09 0.10 0.10 0.11 0.11 0.12 0.12 0.13 0.13 0.13 0.14 0.14 014 0.15 0.15 100:1 1 008 0.09 0.10 0.10 0.11 0.11 0.12 0.12 0.12 0.12 014 0.14 0.15 0.16 0.16 0.16 0.17 0.17 0.18 0.18 0.19 0.19 0.20 2 o.10 0.12 0.14 0.15 0.16 0.17 0.18 0.19 0.19 0.20 0.23 0.25 0.26 0.28 0.29 0.30 0.32 0.33 0.34 0.36 0.37 0.39 0.40 3 0.14 0.18 0.20 0.22 0.23 0.25 0.26 0.27 0.28 0.29 0.32 0.35 0.38 0.40 0.42 0.43 0.45 0.46 0.49 0.51 0.54 0.55 0.57 4 0.16 0.21 0.25 0.28 0.30 0.33 0.35 0.37 0.38 0.40 0.47 0.53 0.58 0.62 0.66 0.70 0.73 0.76 0.82 0.87 0.92 0.96 1.00 20:1 5 0.17 0.24 0.29 0.34 0.38 0.41 0.45 0.48 0.51 0.53 0.66 0.76 0.85 0.93 1.00 1.07 1.13 1.20 1.31 1.42 1.51 1.60 1.69 6 0.21 0.30 0.37 0.43 0.48 0.52 0.56 0.60 0.64 0.67 0.82 0.95 1.06 1.16 1.26 1.34 1.43 1.50 1.65 1.78 1.90 2.02 2.13 7 0.26 0.37 0.45 0.52 0.58 0.64 0.69 0.74 0.78 0.82 1.01 1.17 1.30 1.43 1.54 1.65 1.75 1.84 2.02 2.18 2.33 2.47 2.61 12:1 8 0.31 0.44 0.54 0.63 0.70 0.77 0.83 0.89 0.94 0.99 1.21 1.40 1.57 1.72 1.85 1.98 2.10 2.22 2.43 2.62 2.80 2.97 3.13 9 0.37 0.52 0.64 0.74 0.83 0.91 0.98 1.05 1.11 1.17 1.44 1.66 1.85 2.03 2.19 2.35 2.49 2.62 2.87 3.10 3.32 3.52 3.71 10:1 10 0.43 0.61 0.75 0.87 0.97 1.06 1.15 1.22 1.30 1.37 1.68 1.94 2.16 2.37 2.56 2.74 2.90 3.06 3.35 3.62387 4.11 4.33 11 0.50 0.71 0.86 1.00 1.12 1.22 1.32 1.41 1.50 1.58 1.93 2.23 2.50 2.74 2.95 3.16 3.35 3.53 3.87 4.18 4.47 4.74 4.99 8:1 12.5 0.61 0.86 1.05 1.22 1.36 1.49 1.61 1.72 1.82 1.92 2.35 2.72 3.04 3.33 359 3.84 4.08 4.30 4.71 5.08 5.43 5.76 6.08 15 0.81 1.14 1.40 1.62 1.81 1.98 2.14 2.29 2.43 2.56 3.13 3.62 4.05 4.43 4.79 5.12 5.43 5.72 6.27 6.77 7.24 7.68 8.09 6:1 16.7 0.96 1.36 1.67 1.92 2.15 2.36 2.54 2.72 2.88 3.04 3.72 4.30 4.81 5.27 5.69 6.08 6.45 6.80 7.45 8.04 8.60 9.12 9.62 5:1 20 1.29 1.82 2.23 2.58 2.88 3.16 3.41 3.65 3.87 4.08 5.00 5.77 6.45 7.06 7.63 8.16 8.65 9.12 9.99 10.79 11.54 12.24 12.90 43:1 22 1.51 2.13 2.61 3.02 3.37 3.69 3.99 4.27 4.53 4.77 5.84 6.75 7.54 8.26 8.92 9.54 10.12 10.67 11.68 12.62 13.49 14.31 15.08 4:1 25 1.86 2.63 3.23 3.73 4.16 4.56 4.93 5.27 5.59 5.89 7.21 8.33 9.31 10.20 11.02 11.78 12.49 13.17 14.43 15.58 16.66 17.67 18.63 30 2.51 3.56 4.36 5.03 5.62 6.16 6.65 7.11 7.54 7.95 9.74 11.25 12.57 13.77 14.88 15.91 16.87 17.78 19.48 21.04 22.49 23.86 25.15 3:1 33.3 2.98 4.22 5.17 5.96 6.67 7.30 7.89 8.43 8.95 9.43 11.55 13.34 14.91 16.33 17.64 18.86 20.00 21.09 23.10 24.95 26.67 28.29 29.82 35 3.23 4.57 5.60 6.46 7.23 7.92 8.55 9.14 9.10 10.22 12.52 14.46 16.16 17.70 19.12 20.44 21.68 22.86 25.04 27.04 28.91 30.67 32.32 23:1 40 4.00 5.66 6.93 8.00 8.95 9.80 10.59 11.32 12.00 12.65 15.50 17.89 20.01 21.91 23.67 25.30 26.84 28.29 30.99 33.48 35.79 37.96 40.01 45 4.81 6.80 8.33 9.61 10.75 11.77 12.72 13.60 14.42 15.20 18.62 21.50 24.03 26.33 28.44 30.40 32.24 33.99 37.23 40.22 42.99 45.60 48.07 2:1 50 5.64 7.97 9.76 11.27 12.60 13.81 14.91 15.94 16.91 17.82 21.83 25.21 28.18 30.87 33.34 35.65 37.81 39.85 43.66 47.16 50.41 53.47 56.36 55 6.48 9.16 11.22 12.96 14.48 15.87 17.14 18.32 19.43 20.48 25.09 28.97 32.39 35.48 38.32 40.97 43.45 45.80 50.18 54.20 57.94 61.45 64.78 13:1 57 6.82 9.64 11.80 13.63 15.24 16.69 18.03 19.28 20.45 21.55 26.40 30.48 34.08 37.33 40.32 43.10 45.72 48.19 52.79 57.02 60.96 64.66 68.15 60 7.32 10.35 12.68 14.64 16.37 17.93 19.37 20.71 21.96 23.15 28.35 32.74 36.60 40.10 43.31 46.30 49.11 51.77 56.71 61.25 65.48 69.45 73.21 13:1 66.7 8.44 11.93 14.61 16.88 18.87 20.67 22.32 23.87 25.31 26.68 32.68 37.74 42.19 46.22 49.92 53.37 56.60 59.66 65.36 70.60 75.47 80.05 84.38 70 8.98 12.70 15.55 17.96 20.08 21.99 23.75 25.39 26.93 28.39 34.77 40.15 44.89 49.17 53.11 56.78 60.23 63.48 69.54 75.12 80.30 85.17 89.78 75 9.78 13.83 16.94 19.56 21.87 23.95 25.87 27.66 29.34 30.92 37.87 43.73 48.89 53.56 57.85 61.85 65.60 69.15 75.75 81.82 87.46 92.77 97.79 13:1 80 10.55 14.93 18.28 21.11 23.60 25.85 27.93 29.85 31.66 33.38 40.88 47.20 52.77 57.81 62.44 66.75 70.80 74.63 81.76 88.31 94.41 100.13 105.55 85 11:30 15.98 19.58 22.61 25.27 27.69 29.90 31.97 33.91 35.74 43,78 50.55 56.51 61.91 66.87 71.48 75.82 79.92 87.55 94.57 101.09 107.23 113.03 90 12.02 17.00 20.82 24.04 26.88 29.44 31.80 34.00 36.06 38.01 46.55 53.76 60.10 65.84 71.11 76.02 80.63 84.99 93.11 100.57 107.51 114.03 120.20 95 12.71 17.97 22.01 25.41 28.41 31.12 33.62 35.94 38.12 40.18 49.21 56.82 63.53 69.59 75.17 80.36 85.23 89.84 98.42 106.30 113.64 120.54 127.06 1:1 100 13.36 18.89 23.14 26.72 29.87 32.72 35.34 37.78 40.08 42.24 51.74 59.74 66.79 73.17 79.03 84.49 89.61 94.46 103.48 111.77 119.48 126.73 133.59 Calculated from 65.41 X S2 4.56 X S £ ( + 10,000 + \'+1O,000 + 0.065 , )(721.5) LS = topographic factor = slope length, ft (m X 0.3048) s = slope steepness, in = exponent dependent upon slope steepness (0.2 for slopes < 1 "c, 0.3 for slopes I to 3 0.4 for slopes 3.5 to 4,5" , and 0.5 for slopes > N i \/ t '>''\\'\ 'N N \ \ \• \\ // ' - 29 '/' I - // / / / \ R/// 7 91 -'sq, NN 'N/'N 9''_• // -. " ' -. __// •//;//j / N' 7 • / / - / I N. - / / / / 26 // 280 270 0' 15' 60' LCTS- OFFICE 30 BASIN AREA SCALE: 1" = 60' FOR DESILTATION CALCULATIONS \001017\_offlce\Exhibits\1090desiit.dwq Feb 22, 2012 2:22pm Xrefs: 1017701; 10177UTL; 1017KMAP; 1090KGRD; 1090KUTL