YOLO COUNTY INTEGRATED REGIONAL WATER MANAGEMENT PLAN

Transcription

1 YOLO COUNTY INTEGRATED REGIONAL WATER MANAGEMENT PLAN CHAPTER 1 CHAPTER 2 CHAPTER 3 CHAPTER 4 CHAPTER 5 CHAPTER 6 APPENDIX A OVERVIEW OF IRWMP EFFORT GEOLOGY, HYDROGEOLOGY, AND GROUNDWATER IN YOLO COUNTY AND VICINITY SOILS OF YOLO COUNTY HYDROLOGY OF YOLO COUNTY LAND USE, WATER USE, AND WATER SUPPLIES OF YOLO COUNTY ENVIRONMENTAL WATER RESOURCES OF YOLO COUNTY CALIFORNIA WATER RIGHTS PERTAINING TO WATER RESOURCE MANAGEMENT IN YOLO COUNTY May 2005

2 TABLE OF CONTENTS CHAPTER 3. SOILS OF YOLO COUNTY Organization of Chapter General Soils Map Description Lowland Soils Yolo-Brentwood Association Rincon-Marvin-Tehama Association Capay-Clear Lake Association Sycamore-Tyndall Association Sacramento Association Willows-Pescadero Association Capay-Sacramento Association Upland Soils Corning-Hillgate Association Sehorn-Balcom Association Dibble-Millsholm Association Positas Association Rock land Association Soil Mapping Units Soil Characteristics Hydrologic Soil Groups Hydric Soils Yolo County Soil Summary REFERENCES LIST OF TABLES Table 3-1 Table 3-2 Table 3-3 Summary of Yolo County Soil Mapping Units of Yolo County Infiltration Rates for Hydrologic Soil Groups LIST OF MAPS Map 3-1 Map 3-2 Map 3-3 General Soils Map Hydrologic Soil Groups Hydric Soils Yolo County IRWMP 3-i May 2005

3 CHAPTER 3. SOILS OF YOLO COUNTY This chapter presents soils found within Yolo County and their characteristics. Understanding soils is an important part of integrated regional water management for the County and its planners. Some of the issues related to soils that must be considered include erosion, rainfall runoff, irrigation runoff, and sustainability of agriculture. Also if the County plans to perform active recharge of the groundwater by spreading water on the ground, they would need to look for more permeable soils. Most of the information provided in this chapter is derived from the soil survey of Yolo County conducted by the Natural Resources Conservation Service (NRCS). A more detailed description of the soils of Yolo County is available from the Soil Survey of Yolo County, California (NRCS, 1972). However, this chapter does provide a good synopsis of soils within the County and will be a good reference along with the other chapters contained in the. 3.1 ORGANIZATION OF CHAPTER This chapter first describes the General Soils Map and each soil association within Yolo County. A soil association is a landscape that has a distinctive proportional pattern of soils. It normally consists of one or more major soils and at least one minor soil, and it is named for the major soils. The soils in one association may occur in another, but in a different pattern. The chapter then goes on to explain various soil characteristics that are pertinent to water management in Yolo County. All the soils in the county are described with tables and maps using these characteristics. Yolo County IRWMP 3-1 May 2005

4 3.2 GENERAL SOILS MAP DESCRIPTION Soils within Yolo County can be separated into two classes, Lowland soils and Upland soils. Lowland soils, found on alluvial fans and in basins in eastern Yolo County, are generally well drained to poorly drained while Upland soils, found at higher elevations and terraces in the western portion of the county are somewhat excessively drained to well drained. Map 3.1 shows the distribution of these soil classes in Yolo County. Twelve soil associations exist within Yolo County, seven that belong to the Lowland class and five that belong to the Upland class. These associations are described below and summarized in Table Lowland Soils Soils belonging to this class of soils are found in lowland areas of Yolo County including alluvial fans, basin rims and terraces and in basins. These lowland soils are well drained to poorly drained sandy loams to clays formed in alluvium with relatively level slopes. Lowland Soils make up 63 percent of the county YOLO-BRENTWOOD ASSOCIATION Yolo-Brentwood soils are formed in stream-channel alluvium and are characterized by welldrained silt loams and silty clay loams. On surfacial layers, these soils are grayish-brown silt loam or clay loam and brown, pale brown and grayish-brown silt and silt loam on the subsurface. Slopes range from zero to two percent and elevation ranges from 25 to 400 feet. The Myers, Reiff, Sycamore and Zamora series are minor soils of the Yolo-Brentwood association RINCON-MARVIN-TEHAMA ASSOCIATION The Rincon-Marvin-Tehama association contains well-drained and somewhat poorly drained loams to silty clay loams. Rincon soils are somewhat poorly drained and have a surface layer of Yolo County IRWMP 3-2 May 2005

5 grayish-brown silty clay loam. These soils have a subsoil of grayish-brown silty clay loam and a substratum of light yellowish-brown and pale-brown clay loam. Marvin soils are somewhat poorly drained and have a surface layer of grayish-brown silty clay loam and light silty clay. These soils have a subsoil of dark grayish-brown and grayish-brown silty clay and a substratum of light-brownish-gray and pale-brown silty clay loam. Tehama soils are well drained and have a surface layer of pale-brown loam. These soils have a subsoil of brown, yellowish-brown, and light yellowish-brown clay loam and gravelly loam, and a substratum of light yellowish-brown sandy loam. This formation has slopes that range from zero to two percent and elevations that range from 20 to 500 feet. The Capay, Clear Lake and Hillgate series are minor soils of this association CAPAY-CLEAR LAKE ASSOCIATION The Capay-Clear Lake association consists of moderately well drained to poorly drained silty clays and arid clays found on basin rims and in basins. These soils were formed in alluvium derived from sedimentary rock. The Capay series is moderately well drained and has a surface layer of grayish-brown to dark grayish-brown silty clay and a substratum of pale-brown silty clay. The Clear Lake series is poorly drained, has a surface layer of dark-gray and very dark-gray clay and a substratum of olive-gray clay. Slopes range from zero to two percent and elevations range from ten to 400 feet. The Sycamore series is a minor soil to a small extent as are some recent deposits of coarser surface material SYCAMORE-TYNDALL ASSOCIATION Sycamore-Tyndall association consists of soils that are somewhat poorly drained very fine sandy loams to silty clay loams that are found on alluvial fans formed from mixed sources. The Yolo County IRWMP 3-3 May 2005

6 Sycamore series has a surface layer of grayish-brown silt or silty clay loam and a subsoil of mottled light yellowish-brown silt loam or silty clay loam with a substratum of mottled paleolive loam. Tyndall soils have a surface layer of grayish-brown and light brownish-gray very fine sandy loam. The subsoil is characterized by light brownish-gray to mottled dark to yellowish-brown prominently mottled pale-olive very fine sandy loam with a substratum of distinctly mottled light brownish-gray and mottled yellowish-brown stratified sandy loam to very fine sandy loam. Slopes are generally less than one percent and elevations range from sea level to 70 feet. Minor soils to this association are Lang soils plus small areas of affected alkali and areas that have a silty clay substratum SACRAMENTO ASSOCIATION The Sacramento association consists of poorly drained clays and silty clay loams found in basins. These soils were formed in alluvium from mixed sources. Sacramento soils have a surface layer consisting of mottled gray clay or silty clay loam with a substratum of mottled gray clay. Slopes are generally less than one percent and elevations range from five feet below sea level to 60 feet above sea level. Minor soils to this group include alkali soils found in depression an unnamed coarse-textured soil near sloughs WILLOWS-PESCADERO ASSOCIATION Soils in the Willows-Pescadero association are poorly drained saline-alkali silty clay loams to clays found in basins and were formed in alluvium from mixed and sedimentary rocks. Willows soils have a surface layer of mottled gray and olive-gray clay or silty clay loam with a substratum of mottled olive-gray clay. Pescadero soils have a surface layer of light-gray and olive-gray clay or silty clay loam and a substratum of mottled olive-gray clay. Pescadero soils Yolo County IRWMP 3-4 May 2005

7 have a surface layer consisting of light-gray silty clay loam or silty clay, a subsoil of gray, light olive-gray and pale brown silty clay and silty clay loam. Pescadero soils have a substratum of mottled pale-brown and very pale-brown clay loam and silty loam. Slopes for this association are generally less than one percent and elevations range from sea level to 100 feet. Lang, Laugenour and Sacramento soils are subsoils to this group CAPAY-SACRAMENTO ASSOCIATION The Capay-Sacramento association consists of moderately well drained to poorly drained silty clay loams to clays found in basins formed in alluvium from mixed sources. Capay soils are moderately well drained with a surface layer of grayish-brown and dark grayish-brown silty clay with a substratum of pale-brown silty clay. Sacramento soils are poorly drained with a surface layer of mottled gray clay or silty clay loam and a substratum of mottled gray clay. Slopes are less than one percent and elevations range from five feet below sea level to 60 feet above sea level. Lang, Laugenor and Sacramento soils are minor soils of this association Upland Soils Upland soils are somewhat excessively drained to well-drained loams or gravelly loams to clays. These soils form on uplands or on terraces, weathered from sandstone, shale, and siltstone. Slopes for this class range from two to 75 percent and elevations range from 15 to 3,000 feet. Five associations are classified as Upland soils, and they make up 37 percent of Yolo County CORNING-HILLGATE ASSOCIATION Soils of the Corning Hillgate association are well-drained gravelly loams or loams found on terraces that are formed in alluvium from sedimentary rock and mixed sources. Corning soils have a light-brown gravelly loam and loam surface layer and a sub-soil of red, reddish-yellow Yolo County IRWMP 3-5 May 2005

8 and yellowish-red clay and very gravelly clay. These soils have a substratum that is a reddishyellow very gravelly clay. Hillgate soils have a surface layer of brown loam, a subsoil of strongbrown clay and a substratum of yellowish-brown clay loam. Depth to the clay subsoil ranges from ten to 30 inches for both soils in this association. Slopes range from two to 30 percent and elevations range from 15 to 600 feet. Positas, San Ysidro and Sehron soils are minor soils of this association SEHORN-BALCOM ASSOCIATION The Sehorn-Balcom association consists of well-drained silty clay loams and clays over sandstone formed in softly consolidated sediment. Sehorn soils have a surface layer of palebrown and olive-gray clay or cobbley clay underlain by olive-gray clay. At a depth of 24 to 60 inches, an olive-gray soft, fine-grained sandstone exists. Balcom soils are well drained with a surface layer of pale-brown silty clay loam underlain with a mottled very pale brown silty clay loam. Pale-brown soft calcareous sandstone exists ten to 47 inches below this formation. Slopes generally range from two to 50 percent and elevations range from 100 to 2,000 feet. Corning, Millsholm and Positas soils are minor soils of this association DIBBLE-MILLSHOLM ASSOCIATION The Dibble-Millsholm association consists of well-drained loams to silty clay loams found on sandstone and shale on terraces and uplands. Dibble soils have a brown clay loam surface layer and a yellowish-brown and light olive-brown silty clay and clay subsoil. These soils are underlain by pale-olive very fine sandstone at 20 to 36 inches. Millsholm soils have a light brownish-gray loam surface layer, a subsoil of pale-brown loam and stony loam and are underlain by light-brownish gray shattered shale at ten to 25 inches. Exposed bedrock covers two Yolo County IRWMP 3-6 May 2005

9 to ten percent of Millsholm soils. Slopes for this association range from 30 to 75 percent and elevations range from 300 to 2500 feet. Minor soils of this association are the Balcom and Positas POSITAS ASSOCIATION Soils of the Positas association are well-drained gravelly loams found on old alluvium and dissected soils. These soils have a brown gravelly loam and gravelly sandy clay loam surface layer and a yellowish-red gravelly clay and reddish-brown very gravelly clay subsoil. Slopes range from 15 to 50 percent and elevations range from 400 to 1,500 feet. Balcom and Millsholm soils are minor soils to this association ROCK LAND ASSOCIATION The Rock Land association consists of bare rock and sandy loam to sandstone and shale. A very thin mantle of brown to light yellowish-brown sandy loam over sandstone, shale or serpentine bedrock exists in places. Slopes range from 30 to 75 percent and elevations range from 500 to 3,000 feet. Minor soils of this association are the Millsholm and Positas Soil Mapping Units For the purpose of detailed mapping of soils for site-specific management, the NRCS has created a number of mapping units for Yolo County. Mapping units are groupings of soils based on their shared characteristics. Some mapping units are made up of soils from different series, or different soil phases of the same series. NRCS has created 108 mapping units for Yolo County. Table 3.2 lists these mapping units along with the percentage of Yolo County comprised by each mapping unit. Yolo County IRWMP 3-7 May 2005

10 3.3 SOIL CHARACTERISTICS This section describes various soil characteristics that are pertinent to water management in Yolo County. The characteristics described will be hydrologic soil groups, capability units, storie index, vegetative soil groups, and hydric soils groups. These characteristics will address runoff potential, infiltration potential, erodibility, suitability for agriculture, and plant adaptation and use. Specific soils will be described using these characteristics with tables and maps Hydrologic Soil Groups The NRCS classifies soils into four hydrologic groups based intake of water on bare soil when thoroughly wetted. The four groups, A through D, are as follows: A Soils that have a high infiltration rate even when thoroughly wetted. These soils have a high rate of water transmission and low run off potential. They are deep, are well drained or excessively drained, and consist chiefly of sand, gravel, or both. B Soils that have a moderate infiltration rate when thoroughly wetted. These soils have a moderate rate of water transmission and moderate runoff potential. They are moderately deep or deep, are moderately well drained or well drained, and are medium textured to moderately coarse textured. C Soils that have a slow infiltration rate when thoroughly wetted. These soils have a slow rate of water transmission and high runoff potential. They have a layer that impedes downward movement of water, or they are moderately fine textured or fine textured and have a slow infiltration rate. Yolo County IRWMP 3-8 May 2005

11 D Soils that have a slow infiltration rate when thoroughly wetted. The rate of water transmission is very slow, and runoff potential is very high. In this group are (1) clay soils that have high shrink- swell potential; (2) soils that have a permanent high water table; (3) soils that have a claypan clay layer at or near the surface; and (4) soils that are shallow over nearly impervious material All four hydrologic soil types are present in Yolo County as shown in Map 3.2. Soil Group A, with the highest infiltration rate, is within Cache Creek, particularly where the creek flows eastward after exiting Capay Valley. Overbank deposits from the east-flowing sections of Cache and Putah Creeks are defined by soils with a moderate infiltration rate (Group B), as are the fan deposits from these same drainages where the drainages dissipate into the Sacramento River flood plain. The uplands surrounding the Hungry Hollow area, north of Cache Creek are also partially defined by the distribution of the Group B soils. The soils here are generated from the lower sections of the southerly and easterly dipping Tehama Formation, the porous alluvial and volcaniclastic deposits that comprise the primary aquifer underlying the southern, more populated half of Yolo County. Group C and Group D soils have slow and very slow infiltration rates, and both soil groups have high runoff potential. These soil groups are associated predominately with the western uplands where bedrock is exposed or covered with a soil veneer and with the broad floodplains of lower Cache and Putah Creeks and the Sacramento River, where fines are deposited by stagnated and receding flood waters. Yolo County IRWMP 3-9 May 2005

12 Soils that are excessively and very well-drained have potentially high infiltration rates if they are sufficiently thick and/or overlie other sufficiently porous media. The excessively and very welldrained soils are relatively thin and overlie bedrock. Infiltration is low here compared to the soils found in the more low-lying areas of the county. Table 3.3 shows representative infiltration rates for each soil group Hydric Soils The definition of a hydric soil is a soil that formed under conditions of saturation, flooding or ponding long enough during the growing season to develop anaerobic conditions in the upper part. The concept of hydric soils includes soils developed under sufficiently wet conditions to support the growth and regeneration of hydrophytic vegetation. Soils that are sufficiently wet because of artificial measures are included in the concept of hydric soils. Also, soils in which the hydrology has been artificially modified are hydric if the soil, in an unaltered state, was hydric. Some series, designated as hydric, have phases that are not hydric depending on water table elevation, flooding, and ponding characteristics ( Map 3.3 shows the areas in Yolo County that are hydric. 3.4 YOLO COUNTY SOIL SUMMARY Table 3.1 presents all the soils in Yolo County with all the characteristics that were described above. More detailed information of Yolo County soils may be obtained from the Soil Survey of Yolo County (NRCS, 1972) and the Soil Survey Geographic (SSURGO) database for Yolo County (NRCS, 2003). Yolo County IRWMP 3-10 May 2005

13 REFERENCES USDA/NRCS, Soil Survey of Yolo County, California, June 1972 USDA/NRCS, Urban Hydrology for Small Watersheds (Tech Release 55.), 1986 USDA/NRCS, Soil Survey Geographic (SSURGO) database for Yolo County, California, May 2003 USDA/NRCS website on Hydric Soils ( Yolo County IRWMP 3-11 May 2005

14 Tables

15 Table 3.1 Summary of Yolo County Soil Associations SOIL ASSOCIATION Yolo-Brentwood GEOGRAPHIC TERRAIN OF OCCURRENCE SOIL COMPOSITION Lowlands: Alluvial fans Silt and Silty Clay Loams Rincon-Martin-Tehama Lowlands: Alluvial fans and basin rims Capay-Clear Lake Sycamore-Tyndall Association Lowlands: Basins and basin rims Sacramento Lowlands: Basins Loam and Silty Clay loam SOIL SOURCE Alluvium from sedimentary rock Alluvium from sedimentary rock Silty Clay and Clay Alluvium from sedimentary rock Lowlands: Alluvial fans Fine-sandy loam to siltly clay loam Clays Willows-Pescadero Lowlands: Basins Saline-alkali silty clay loam and clays Capay-Sacramento Lowlands: Basins Silty clay loams, silty clays, and clays Alluvium from mixed sources Alluvium from mixed sources Alluvium from sedimentary rock, mixed sources Alluvium from mixed sources PERCENT OF YOLO COUNTY AREA (%) ELEVATION RANGE (feet above Mean Sea Level) SLOPE RANGE (%) RANGE OF ANNUAL RAINFALL (inches) NATIVE VEGETATION to to 2 16 to 22 Grasses and forbs to to 2 16 to 20 Grasses, forbs, scattered oaks to to 2 16 to 20 Grasses and forbs 5 0 to 70 < 1 16 to 18 Grasses and forbs 8-5 to 60 < 1 16 to 19 Grasses and forbs 4 0 to 100 < 1 16 to 20 Grasses, forbs, salt grass, pickleweed, other salttolerant plants 9-5 to 60 < 1 16 to 20 Grasses and forbs CULTIVATION Irrigated orchards, row crops, field crops, truck crops, and pasture; dryfarmed grain Irrigated orchards, row crops, field crops; dryfarmed grain Irrigated row crops, field crops; dryfarmed field crops and pasture Irrigated row crops, hay, orchards, and pasture; dryfarmed grain. Irrigated row crops, truck crops; dryfarmed field crops Alkali-tolerant irrigated row crops, field crops, and pasture Summer-irrigated row crops, field crops, and pasture; dryfarmed field crops and grain ANNUAL RANGE OF FROST-FREE DAYS (days) PREDOMINATE WILDLIFE MINOR SOILS 230 to 280 Upland game birds Myers, Reiff, Sycamore, Zamora 265 to 280 Upland game birds Capay, Clear Lake, Hillgate 280 Upland game birds and waterfowl 230 Waterfowl Sycamore Lang 275 Upland game birds Unnamed 280 Waterfowl 275 to 280 Upland game birds and waterfowl Lang, Laugenour, Sacramento Lang, Laugenour, Sacramento Corning-Hillgate Uplands: Terraces Gravelly loams, loams Sehorn-Balcom Dibble-Millsholm Positas Rock Land Uplands: Dissected Uplands underlain by fine-grained sandstone Uplands: Dissected alluvial terraces and uplands underlain by sandstone and shale Uplands: Dissected alluvial terraces Uplands: Rock outcroppings Silty clay loams, clays Silty clay loams, and clay loams Gravelly loams, loams Rock outcrops and areas of sandy loam over rock Alluvium from sedimentary rock, mixed sources Sediment weathered from fine-grained sandstone Sediment weathered from sedimentary bedrock Sediment weathered from sedimentary bedrock 7 15 to to to 20 Grasses, forbs, scattered oaks and brush to 2,000 2 to to 24 Grasses and forbs to 2, to to 24 Grasses, forbs, scattered oaks to 1, to to 24 Grasses, forbs, scattered oaks, brush Not applicable to 3, to to 24 Chamise (where soil is present) Dryfarmed grain, pasture 265 to 280 Upland game birds Positas, San Ysidro, Sehorn Dryfarmed field crops, pasture 250 Upland game birds Corning, Millsholm, Positas Rangeland 230 to 250 Deer Balcom, Positas Rangeland 230 Deer Balcom, Millsholm Not applicable 230 Deer Millsholm, Positas

16 Table 3.2 Mapping Units of Yolo County Mapping Unit Soil name Percentage of Yolo County AaA Arbuckle Gravelly Loam, 0 To 2 Percent Slopes 0.4 AaB Arbuckle Gravelly Loam, 2 To 5 Percent Slopes 0.2 BaD3 Balcom Silty Clay Loam, 5 To 15 Percent Slopes, Severely Eroded < 0.1 BaE2 Balcom Silty Clay Loam, 15 To 30 Percent Slopes, Eroded 0.8 BaF2 Balcom Silty Clay Loam, 30 To 50 Percent Slopes, Eroded 1.9 BaG3 Balcom Silty Clay Loam, 50 To 75 Percent Slopes, Severely Eroded < 0.1 BdF2 Balcom-Dibble Complex, 30 To 50 Percent Slopes, Eroded 2.5 BrA Brentwood Silty Clay Loam, 0 To 2 Percent Slopes 3.6 Ca Capay Silty Clay 5.3 Cb Capay Silty Clay, Flooded 0.4 Cc Capay Soils, Flooded 1.7 Ch Clear Lake Silty Clay Loam < 0.1 Ck Clear Lake Clay 1.1 Cn Clear Lake Soils, Flooded 1.8 CrE2 Climara Clay, 2 To 30 Percent Slopes, Eroded < 0.1 CtD2 Corning Gravelly Loam, 2 To 15 Percent Slopes, Eroded 3.4 CtE2 Corning Gravelly Loam, 15 To 30 Percent Slopes, Eroded 0.2 DaF2 Dibble Clay Loam, 30 To 50 Percent Slopes, Eroded 2.8 DaG2 Dibble Clay Loam, 50 To 75 Percent Slopes, Eroded 0.4 DbE2 Dibble-Millsholm Complex, 9 To 30 Percent Slopes, Eroded 0.1 DbF2 Dibble-Millsholm Complex, 30 To 50 Percent Slopes, Eroded 0.3 DbG2 Dibble-Millsholm Complex, 50 To 75 Percent Slopes, Eroded 0.9 GP Gravel Pits < 0.1 HcA Hillgate Loam, 0 To 2 Percent Slopes 0.6 HcC2 Hillgate Loam, 2 To 9 Percent Slopes, Eroded 0.2 HdA Hillgate Loam, Moderately Deep, 0 To 2 Percent Slopes 0.4 HdC Hillgate Loam, Moderately Deep, 2 To 9 Percent Slopes 0.2 La Lang Sandy Loam 0.5 Lb Lang Sandy Loam, Deep 0.3 Lc Lang Sandy Loam, Deep, Flooded < 0.1 Ld Lang Silt Loam 0.1 Lg Laugenour Very Fine Sandy Loam 0.3 Lh Laugenour Very Fine Sandy Loam, Flooded 0.2 Lk Laugenour Very Fine Sandy Loam, Deep, Flooded 0.2 Lm Loamy Alluvial Land 0.3 M-W Miscellaneous Water < 0.1 Ma Made Land 0.7 Mb Maria Silt Loam 0.3 Mc Maria Silt Loam, Flooded 0.1 Md Maria Silt Loam, Deep 0.3 Mf Marvin Silty Clay Loam 3.2 Mk Merritt Silty Clay Loam 0.4 Mn Merritt Silty Clay Loam, Deep 0.3 Mo Merritt Silty Clay Loam, Deep, Drained 0.3 Mp Merritt Complex, SalineAlkali 0.1 MrG2 Millsholm Rocky Loam, 15 To 75 Percent Slopes, Eroded 4.7 Ms Myers Clay 1.4

17 Mapping Unit Soil name Percentage of Yolo County Oa Omni Silty Clay Loam < 0.1 Ob Omni Silty Clay 0.5 Pa Pescadero Silty Clay 0.1 Pb Pescadero Silty Clay, SalineAlkali 0.8 Pc Pescadero Soils, Flooded 0.5 PfE2 Positas Gravelly Loam, 15 To 30 Percent Slopes, Eroded 0.3 PfF2 Positas Gravelly Loam, 30 To 50 Percent Slopes, Eroded 1.2 PfF3 Positas Gravelly Loam, 30 To 50 Percent Slopes, Severely Eroded 0.7 Ra Reiff Very Fine Sandy Loam 1 Rb Reiff Gravelly Loam 0.3 Rg Rincon Silty Clay Loam 3.8 Rh Riverwash 0.7 Rk Riz Loam 0.2 Rn Riz Loam, Flooded 0.1 RoG Rock Land 4.9 Sa Sacramento Silty Clay Loam 0.9 Sb Sacramento Silty Clay Loam, Drained 0.4 Sc Sacramento Clay 5.5 Sd Sacramento Clay, Drained 0.4 Se Sacramento Clay, Flooded < 0.1 Sf Sacramento Clay, Deep < 0.1 Sg Sacramento Soils, Flooded 1.9 Sh San Ysidro Loam 0.7 SkD Sehorn Clay, 2 To 15 Percent Slopes 0.9 SkE2 Sehorn Clay, 15 To 30 Percent Slopes, Eroded 0.3 SkF2 Sehorn Clay, 30 To 50 Percent Slopes, Eroded 0.3 SlD Sehorn Cobbly Clay, 2 To 15 Percent Slopes 0.3 SmD SehornBalcom Complex, 2 To 15 Percent Slopes 2.5 SmE2 SehornBalcom Complex, 15 To 30 Percent Slopes, Eroded 2.7 SmF2 SehornBalcom Complex, 30 To 50 Percent Slopes, Eroded 1.7 Sn Soboba Gravelly Sandy Loam 0.3 So Sycamore Silt Loam 0.7 Sp Sycamore Silt Loam, Drained 0.9 Sr Sycamore Silt Loam, Flooded 0.3 Ss Sycamore Silty Clay Loam 0.8 St Sycamore Silty Clay Loam, Drained 1.2 Su Sycamore Complex 0.5 Sv Sycamore Complex, Drained 1.4 Sw Sycamore Complex, Flooded 0.8 TaA Tehama Loam, 0 To 2 Percent Slopes 2.5 TaB Tehama Loam, 2 To 5 Percent Slopes 0.2 Tb Tyndall Very Fine Sandy Loam 0.6 Tc Tyndall Very Fine Sandy Loam, Drained 0.3 Td Tyndall Very Fine Sandy Loam, Flooded 0.1 Te Tyndall Very Fine Sandy Loam, Deep 0.4 Tf Tyndall Silty Clay Loam 0.1 Va Valdez Silt Loam < 0.1 Vb Valdez Silt Loam, Deep 0.3 Vc Valdez Complex, Flooded < 0.1 W Water 1.2

18 Mapping Unit Soil name Percentage of Yolo County Wa Willows Silty Clay Loam 0.2 Wb Willows Clay 0.9 Wc Willows Clay, Alkali 0.4 Wd Willows Clay, Alkali, Drained < 0.1 Wf Willows Clay, Alkali, Flooded 0.4 Wg Willows Soils, Flooded 0.2 Wm Willows Clay, Marly Variant 0.2 Wn Willows Clay, Marly Variant, SalineAlkali < 0.1 Ya Yolo Silt Loam 6.2 Yb Yolo Silty Clay Loam 0.8 Za Zamora Loam 0.5 Total = 100%

19 Table 3.3 Infiltration Rates for Hydrologic Soil Groups Group Minimum Infiltration Texture Rate (in/hr) A Sand, loamy sand or sandy loam B Silt loam or loam C Sandy clay loam D Clay loam, silty clay loam, sandy clay, silty clay or clay Adapted from Urban Hydrology for Small Watersheds Tech. Release 55. Soil Conservation Service, 1986.

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