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HomeMy WebLinkAboutSouthridge Development Flood Flow Bulking Factor for DeClez ChannelSOUTHRIDGE VILLAGE DEVELOPMENT FONTANA, CALIFORNIA FLOOD FLOW BULKING FACTOR EVALUATION DECLEZ CHANNEL AND TRIBUTARIES PREPARED FOR CREATIVE COMMUNITIES PREPARED BY BOYLE ENGINEERING CORPORATION SAN DIEGO, CALIFORNIA TABLE OF CONTENTS INTRODUCTION DESCRIPTION OF THE WATERSHED ESTIMATED SEDIMENT PRODUCTION AND TRANSPORT WITHIN THE WATERSHED CONCLUSIONS FIGURES No. 1 Declez Channel Watershed Showing Declez Channel Alignment APPENDIX Sediment Production Computations Revised Flaxman Method Universal Soil Loss Equation Page No. 1 3 7 12 6 INTRODUCTION The Southridge Village project being planned by Creative Communities will require the installation of flood control and drainage facilities. These facilities will include a trapezoidal section concrete lined main channel (Declez Channel); a tributary channel to drain the low area between the main channel and the Jurupa Mountains; and storm drain facilities to collect local runoff and deliver to the main channel. The planned layout for these facil- ities is shown on Figure 1. The locations of the storm drain facilities indicated on this figure are subject to change. In areas where large amounts of sediment are produced by major storms and delivered to the channel system the sediment content of the flood flows becomes a significant part of the flood volume that is transported by the channel system. Consequently, the required channel capacities have to be increased to contain this additional bulking caused by the sediment content. The purpose of this study is to estimate the amounts of sediment that will be produced and transported to the channel system during the period of runoff of a major storm (100 -year return period). This volume of sediment will be con- sidered in relationship to the estimated volume of water runoff to determine the need for additional capacity to contain the sediment content. The required additional capacity is expressed as a bulking factor to be applied to the estimated capacity required for water runoff. - 1 - ............ 69 Traile" Jl t"dustrialsle . ....... . Park• a P�pds Well n Q J4---- ------- PA CIFIC 960 smum-Kaiser.' Ifoo AVE ! r /094 P W .Ziij CRes,--_: ........ 4,1 W------- 2000 4000 FEET. ch Jurupa Hills ..... all: Well -950 1049 '064— Wet: t ifo ------------ 930 41 7: -------------- -- ----- - ------- --3Z 5�_ - -- ---- ------------------ 7 0 Well I too .&;fton MAPLAY 33 AVE Weil - _870 - Ea. q A R C 41 RIVE DE CO YtiOD -7 t f 0 % ....... ... h 9 IZ NE R I FIGURE I . SOUTHRIDGE VILLAGE DECLEZ CHANNEL ALIGNMENT ALTERNATIVE I raf3o4*-- mrxWjeorr4 Carr� . consumnQ enqlnews 1 a9rchitacts MAY IS, 1981 r k, DESCRIPTION OF THE WATERSHED The total drainage area into the channel system is about 7,000 acres (10.91 square miles). It is bounded on the north by the San Bernardino Freeway, on the east by Palmetto Avenue, on the south by the ridge of the Jurupa Moun- tains, and on the west by the slope break east of the San Sevaine Channel. The major drainageway through this area is the Declez Channel which extends from Palmetto Avenue to the junction with the Fontana Channel, which is a continuation of the Declez Channel in Riverside County. The area south of Jurupa Avenue is characterized by a variety of land uses including agricultural but is primarily open space and fallow land. Low- density residential development is presently underway within the northwest portion with clusters of residential development and agricultural uses north of Jurupa Avenue. The Southridge Village development being planned by Creative Communities will occupy approximately 2560 acres in the southern portion of the area. This development will be bounded on the north by Jurupa Avenue, on the west by Mulberry Avenue, on the south by the San Bernardino/Riverside County line and on the east by Sierra Avenue. The city of Fontana anticipates that the total drainage area except the Jurupa Mountain area will be in urban development ultimately. The land slopes within the area are generally within the range of one to two percent except for the Jurupa Mountain area where slopes are generally 25 to 35 percent. - 3 - The soils in the valley area with gentle slopes are predominantly Delhi fine sand (Db) and Tujunga loamy sand (Tu B). Small areas of other sandy soil types are included in the area with similar characteristics. These soils are generally described for this slope category as somewhat excessively drained to excessively drained, very deep soils on alluvial fans or alluvial valley floors. The Soil Survey of San Bernardino County Southwestern Part, California, pre- pared by the USDA Soil Conservation Service, et al, describes these soils in part as follows: Delhi fine sand (Db) - This nearly level to strongly sloping soil is on alluvial fans that have been reworked by wind action. Runoff is very slow, and the hazard of soil blowing is generally moderate. Estimated soil properties: Depth to bedrock or hardpan - greater than 5 feet Depth from surface of typical profile - 0-18 inches -fine sand 18-60 inches -sand Percentage passing sieve No. 4 (4.7 mm) - 100 No. 10 (2.0 mm) - 90-100 No. 40 (0.42 mm) - 50-70 No. 200 (0.074 mm) - 5-10 Permeability - 6.0 to 20.0 inches/hour Hydrologic Soil Group - B (above average infiltration rate) - 4 - Tujunga loamy sand (TUB) - This nearly level to gently sloping soil is on broad, long alluvial fans. Runoff is slow to very slow. The hazard of water erosion is slight, but the soil will blow if left unprotected. The hazard to soil blowing is moderate to high on bare soil. Estimated soil properties: Depth to bedrock or hardpan - greater than 5 feet Depth from surface of typical profile 0-60" loamy sand and coarse sand Coarse fraction greater than 3 inches - 0-5 percent Percentage less than 3 inches passing sieve No. 4 (4.7mm) - 100 No. 10 (2.0 mm) - 55-100 No. 40 (0.42 mm) - 25-50 No. 200 (0.074 mm) - 5-20 The soils in the Jurupa Mountain area are predominantly Cieneba-Rock outcrop complex (Cr). This steep complex is described as occupying areas on uplands. It is about 60 percent Cieneba sandy loam, and has 30 to 50 percent slopes and 30 percent granitic rock outcrops. The Cieneba soil has the profile described as representative of the series. Included with this complex in mapping are small areas of soils that have moderate sheet and rill erosion, places where slopes exceed 50 percent, and small areas where slopes are 15 to 25 percent. Also included are small areas that consist mainly of rock outcrop. - 5 - Runoff is rapid and the hazard of erosion is moderate if soils are burned over or overgrazed. Estimated soil properties: Depth to rock or hardpan - 1-1/2 feet Depth from surface of typical profile 0-14 inches - sandy loam 14 inches - weathered granitic rock Coarse fraction greater than 3 inches - 0-10 percent Percentage less than 3 inches passing sieve No. 4 (4.7 mm) - 90-100 No. 10 (2.0 mm) - 90-100 No. 40 (0.42 mm) - 50-65 No. 200 (0.074 mm) - 25-35 - 6 - ESTIMATED SEDIMENT PRODUCTION AND TRANSPORT WITHIN THE WATERSHED Eroded materials from a drainage area may be transported through the flood channels and compose a large percentage of the volume of the total flow. Under these conditions the estimated peak flood flows of clear water determined in the hydrologic analysis must be increased by a bulking factor because of the transported sediment to determine the required capacity of flood channels. A large percentage of the gross erosion from a watershed may be transported to the channel location if the grades are sufficiently steep to transport the materials in the flood flows. The transport capability of the flood flows is dependent on the velocity of the flow and the characteristics of the eroded materials including size, shape, density, etc. Various methods have been used to estimate sediment bulking factors for flood flows. These methods are largely based on the gross erosion characteristics of a watershed. The Los Angeles County Flood Control District (LACFCD) procedure for estimating bulking factors is based on runoff and sediment produced by a major storm on a recently burned watershed. The bulking factor was determined as 100 percent with a sediment production rate of 120,000 cubic yards per square mile. The formula used for estimating bulking factor for a particular watershed is: 1/2 j mass debris potential - cu. yds./sq. mi. + 1) x 100 120,000 If the rate of sediment production is 120,000 cu.yds/sq.mi. the bulking factor would be 100 percent which is the case on which the formula is based. - 7 - This formula includes a large safety factor for watersheds with low sediment production rates. If the watershed is determined as having no sediment produc- tion the computed bulking factor would still be 50 percent. However, it is stated in their procedures that "This percentage increase is applied to the peak flow rate, where the entire watershed area is considered to be debris productive, and on a proportionate basis with respect to produc- tive and non-productive areas where debris control structures or developments within the watershed would cause a decrease in transportable debris quantities." The Declez Channel watershed has two portions having different characteristics. The alluvial valley area with slopes generally in the range of one to two percent has an area of about 5700 acres (8.9 square miles). The Jurupa Mountain area with slopes generally in the range of 25 to 35 percent has an area of about 1300 acres (2.0 square miles). The alluvial valley area has soils that are very erosion resistant on the prevailing slopes with slow rates of runoff. The soil particle sizes tend to be primarily coarse sand with very small percentages that would be classified as silt. with the slow rates of runoff and low velocities sheet and rill erosion will not dislodge large amounts of sediment and the sand particles would not be transported in large quantities to the stream system. The Jurupa Mountain area has soils that are moderately erosion resistant even on the prevailing steep slopes. The subdrainage areas are very small and large concentrations of runoff do not occur. There are no.raw gullies in the area. Shallow rills in the drainageways are checked from eroding deeper by rock outcrops. There is no evidence of sediment discharge and deposition onto the flatter areas at the base of the hills. It is not planned that this area will be developed or used in a way that will cause soil disturbance. The only significant soil disturbance in the area at present in from roads and motorcycle tracks at the base of the hills. Several methods are available for estimating the mass debris potential or sediment yields from natural watersheds. Of these Elliott M. Flaxman's revised method is considered appropriate for southern California as it was developed from data compiled from 11 western states; Arizona, California, Colorado, Idaho; Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. Applying the revised Flaxman method, the estimated mean annual sediment yield for the 5700 acre alluvial plain portion of the watershed was estimated as 26 cu. yds./square mile (see Appendix). The 100 -year return period flood generally produces from 8 to 10 times the mean annual sediment production. Assuming a multiple of 10, the sediment yield would be 260 cu. yds./square mile. For the total 5700 acre.(8.9 sq. mi.) drainage area, the 100 -year, return period flood is estimated to produce a total of 2314 cu. yds., or 1.43 acre-feet. For the 1300 acre Jurupa Mountain area the estimated mean annual sediment yield was estimated as 645 cu. yds./square mile. The 100 -year return period flood would produce 6450 cu. yds./sq. mi. (10 x 6450). For the total 1300 acre (2.0 sq. mi.) drainage area the 100 -year return period flood is estimated to produce 12,900 cu. yds., or 8.0 acre-feet. - 9 - On the basis of these estimates the total drainage area (10.9 sq. mi.) would produce 9.4 acre-feet of sediment during a storm having a 100 -year return period. The estimated volume of runoff that is estimated to occur with a 6 - hour duration, 100 -year return period flood is 690 acre-feet. The estimated total gross sediment production is 1.36 percent of the estimated runoff volume (9.4/690). A large part of the sediment produced, especially from the Jurupa Mountain area will be deposited within the area and will not be transported to the channel system. Using the LACFCD bulking factor formula, the required bulking factor would be: 1%2 1.391.6 + 1� x 100 = 50.58 percent. 120,000 Without the factor of safety, the bulking factor would be: 1396 x 100 - 1.08 percent. 120,000 This would be reduced to insignificance when the low delivery rates over the alluvial plain are considered. The Universal Soil Loss Equation is a method for predicting rainfall erosion losses with consideration of the various parameters which affect erosion on a particular watershed. This procedure is explained in a publication "Pre- dicting Rainfall Erosion Losses" developed by the USDA in cooperation with Purdue Agriculture Experiment Station, December, 1978. - 10 - This procedure may be used for predicting gross erosion from a storm of specified return period but is considered more accurate for prediction of longtime averages. For conditions affecting the equation parameters for the alluvial plain por- tion of this watershed the estimated average annual rate of sediment produc-. tion is 74 tons/sq. mi., or 659 tons/yr. for 8.9 sq. mi. area. For the Jurupa Mountain portion of the area the estimated average annual rate of. sediment production is 426 tons/sq. mi. or 852 tons per year for the 2.0 square mile area. The total estimated sediment production per year for the total drainage area of 10.9 square miles is 1511 tons/year, or about 0.94 acre-feet. Assuming that the 100 -year return period storm produces 10 times the average annual amounts a total of 9.4 acre-feet would be produced. , CONCLUSIONS Gross sediment production in the drainage area of the Declez Channel is estimated to be very small as compared to the volume of runoff produced by the 6 -hour duration 100 -year return period flood flow (volume of sediment produced is about 1.4 percent of the runoff volume). The major portion of this sediment is produced by the Jurupa Mountain area included in the drainage area. However, sediment produced by the mountain area must be transported over considerable lengths of relatively flat alluvial plain area before it can enter the channel system. The particle size distribution of all soils in the drainage area into Declez Channel indicates that all but a small portion is relatively coarse sand that could not be transported effectively over the alluvial plain with the velocities of flow that would prevail. Consequently, these analyses have indicated that an extremely small amount of sediment in relationship to the flood volume will enter the channel system, thus adding an insignificant amount of volume to the flood flows. Furthermore, as the land use in this area is changed from agriculture and open space to urban use even the small amounts of sediment produced at present will be greatly reduced. Studies have indicated that with mature urban development sediment production rates will be reduced by about 90 percent of that produced by land uses now current in this area. The hydrologic analyses for this area have indicated that peak flood flows that will occur with full urban development will be about 20 percent greater than occur under existing land use. The channel system will be constructed to contain capacities required for these ultimate development conditions. On the basis that these channels will have excess capacities of 20 percent for - 12 - present land use, and as urban development occurs sediment production will be reduced progressively, it appears inappropriate to provide any additional capacity because of possible bulking by the sediment content of the flood flows. The velocities of overland flows with the more frequently occurring storm runoff will be very low and these flows will be able to transport only very fine sand or silt particles. When these particles enter the storm drain system very low velocities will continue to transport the particles entering the system. Providing a minimum velocity of 5 feet/sec. with the more frequently occurring flows appears to be more than sufficient. - 13 - APPENDIX SEDIMENT PRODUCTION COMPUTATIONS ALLUVIAL PLAIN AREA 5700 ACRES (8.9 SQ. MI.) (EXCLUDING JURUPA MOUNTAIN AREA) Revised Flaxman Method The equation used in the revised Flaxman method is: log (Y+100) = 524.37231 - 270.65625 log (X1 + 100) + 6.41730 log (X2 + 100) - 1.70177 log (X3 + 100) + 4.03317 log (X4 + 100) + 0.99248 log (X5 + 100) in which Y = mean annual sediment production - tons/sm X1= ay. an. precip. (in.)/ay. an. temp. (°F) X2= weighted average slope X3= percentage of soil particles coarser than 1.0 mm X4= 0 (when more than 25 percent of soil particles are coarser than 1.0 mm) X5= 50% chance of occurrence flood flow-csm For the Shay Meadow watershed the following values of the variable parameters were determined as follows: X1= 22"/64°F = 0.344 X2= 1.25% X3= 40% X4= 0 X5= 50 csm Using these parameters sediment production was computed: log (Y + 100) = 524.37231 -270.65625 log (0.344 + 100) -541.71616 +6.41730 log (1.25 + 100) +12.86922 -1.70177 log (40 + 100) -3.65222 +4.03317 log (0 + 100) +8.06634 +0.99248 log (50 + 100) +2.15973 2.51935 Y + 100 = 126 Y = 26 tons/sm = 26 cu. yds./sm (approx.) - mean annual sediment production SEDIMENT PRODUCTION COMPUTATIONS JURUPA MOUNTAIN AREA - 1300 ACRES (2.0 SQ. MI.) Revised Flaxman Method The equation used in the revised Flaxman method is: log (Y+100) = 524.37231 - 270.65625 log (X1 + 100) + 6.41730 log (X2 + 100) - 1.70177 log (X3 + 100) + 4.03317 log (X4 + 100) + 0.99248 log (X5 + 100) in which Y = mean annual sediment production - tons/sm X1= ay. an. precip. (in.)/ay. an. temp. (°F) X2= weighted average slope X3= percentage of soil particles coarser than 1.0 mm X4= 0 (when more than 25 percent of soil particles are coarser than 1.0 mm) X5= 50% chance of occurrence flood flow-csm For the Shay Meadow watershed the following values of the variable parameters were determined as follows: X1= 22"/64°F = 0..344 X2= 30% X3= 40% X4= 0 X5= 55 csm Using these parameters sediment production was computed: log (Y + 100) = 524.37231 -270.65625 log (0.344 + 100) -541.71616 +6.41730 log (30 + 100) +13.56581 -1.70177 log (40 + 100) -3.65222 +4.03317 log (0 + 100) +8.06634 +0.99248 log (55 + 100) +2.17386 2.80994 Y + 100 = 330 Y = 645 tons/sm = 645 cu. yds./sm (approx.) = mean annual sediment production 1 SEDIMENT PRODUCTION COMPUTATIONS ALLUVIAL PLAIN AREA - 5700 ACRES (8.9 SQ. MI.) (EXCLUDING JURUPA MOUNTAIN AREA) Universal Soil Loss Equation The Universal Soil Loss Equation is: A = RKLSCP in which the parameters for Shay Meadow watershed were determined as follows: A = Computed soil loss - tons/ac./yr. R = Rainfall factor = 50 K = Soil erodibility factor = 0.24 LS = Topographic factor = 0.23 Slope length assumed - 500 feet Slope steepness = 1.25 percent. C = Cover and management factor = 0.042 Idle land with 60% ground cover P = Support practice factor = 1 A = 50 x 0.24 x 0.23 x 0.042 x 1 = 0.11592 tons/ac./yr. = 0.11572 x 640 = 74 tons/sm/yr. (estimated average annual rate) Assume 100 -year flood produces 10 times the average annual sediment production Estimated sediment yield for 100 -year flood = 10 x 74 = 740 tons/sm 740 cu. yds./sm (approx.) SEDIMENT PRODUCTION COMPUTATIONS JURUPA MOUNTAIN AREA - 1300 ACRES (2.0 SQ. MI.) Universal Soil Loss Eauation The Universal Soil Loss Equation is: A = RKLSCP in which the parameters for Shay Meadow watershed were determined as follows: A = Computed soil loss - tons/ac./yr. R = Rainfall factor = 50 K = Soil erodibility factor = 0.24 LS = Topographic factor = 18.5 r Slope length assumed - 500 feet Slope steepness = 30 percent C = Cover and management factor = 0.003 Range with 95+% ground cover P = Support practice factor = 1 A = 50 x 0.24 x 18.5 x 0.003 x 1 = 0.666 tons/ac./yr. = 0.666 x 640 = 426 tons/sm/yr. (estimated average annual rate) Assume 100 year flood produces 10 times the average annual sediment production Estimated sediment yield for 100 -year flood = 10 x 426 = 4260 tons/sm 4260 cu. yds./sm (approx.)