Science Direct Geomorphology. Sediment Deposition in the Flood
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ARTICLE IN PRESS Geomorphology xx (2004) xxx–xxx www.elsevier.com/locate/geomorph Sediment deposition in the flood plain of Stemple Creek Watershed, northern California Jerry C. Ritchiea,*, Vernon L. Finneyb, Kenneth J. Osterc, Carole A. Ritchied a USDA ARS Hydrology and Remote Sensing Laboratory, Beltsville, MD 20705, USA b USDA NRCS California State Office, Davis, CA 95616, USA c USDA NRCS Templeton Service Center, Templeton, CA 93465, USA d Botanical Consultant, Laurel, MD 20708, USA Received 16 July 2003; received in revised form 27 January 2004; accepted 30 January 2004 Abstract Over the past 150 years, major land use changes have occurred in the Stemple Creek Watershed in northern California that have caused erosion to move soils from the upland to the flood plain, stream channels, and the bay. The purpose of this study is to document the recent (1954 to present) sediment deposition patterns in the flood plain area adjacent to Stemple Creek using the 137Cesium technique. Sediment deposition ranged from 0.26 to 1.84 cm yearÀ 1 for the period from 1964 to 2002 with an average of 0.85 F 0.41 cm yearÀ 1. Sediment deposition rates were higher for the 1954 to 1964 period with a range of 0.31– 3.50 cm yearÀ 1 and an average of 1.29 F 1.04 cm yearÀ 1. These data indicate that sediment deposition in the flood plain has decreased since the middle 1950s, probably related to reduction in row crop agriculture and an increase in pasturelands. This study shows that the flood plains in the Stemple Creek Watershed are a significant sink for the soils being eroded from the upland area. Given the significance of the flood plain for trapping eroded materials before they reach the stream channels or the bay, efforts need to be made to manage these flood plain areas to insure that they do not change and become a source rather than a sink for eroded materials as improved management practices on the upland areas reduce sediment input to the flood plain. D 2004 Elsevier B.V. All rights reserved. Keywords: Flood plain; Deposition; Erosion; 137Cesium; California 1. Introduction Stemple Creek Watershed. Much of these lower slopes and bottomlands were cleared and drained for agri- Over the past 150 years, major changes have culture in the 1860s. Erosion accelerated under these occurred in the land use patterns in the Stemple Creek conditions and stream channels and bays filled with Watershed in northern California. Riparian forests and sediment, further reducing the area occupied by ripar- marshes are believed to have been more widespread in ian forests and marshes (Harvey, 1990). the areas adjacent to the stream channel of the Stemple Creek is part of the coastal lands in the Bodega Bay–Tomales Bay area that has a long * Corresponding author. Tel.: +1-301-504-7940; fax: 1-301- history of erosion and sedimentation problems. Geo- 504-8930. logically, the California coastal range is young and E-mail address: [email protected] (J.C. Ritchie). still uplifting. A coastal uplift rate of 0.07–0.08 cm 0169-555X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2004.01.009 GEOMOR-01511; No of Pages 14 ARTICLE IN PRESS 2 J.C. Ritchie et al. / Geomorphology xx (2004) xxx–xxx yearÀ 1 has been calculated for the Point Reyes nuske-Chatham, 1994). The present low gradient Peninsula, CA (K. Grove, Department of Geoscience, stream system (0.000415 m mÀ 1) is conducive to San Francisco University, personal communication, deposition, confirmed by sediment in-filled stream 2001). The hills are therefore prone to landslides, channels in the upper watershed. As Stemple Creek slumping, and erosion contributing to high naturally flows coastward, the fjord-like qualities of steep and occurring erosion rates. In addition, historically the twisting uplands become the dominating character of combination of row crop agriculture, cultivation, and the landscape. year-round grazing on moderately erodible Steinbeck Finney (2002) used the AGricultural NonPoint (Mollic Haploxeralfs), Sebastopol (Typic Haploxer- Source (AGNPS) model to estimate soil loss for four ults), and Tomales (Ultic Paleustalfs) soils has land use scenarios and estimated that 11% of the resulted in erosion on the watershed with subsequent eroded material from the uplands reached the bay. sediment deposition in the flood plains, stream chan- The purpose of this study is to document the recent nels, and bays causing loss of open water. In the late (1954 to present) sediment deposition patterns in the 19th and early 20th century, Estero Americano, north flood plain area adjacent to Stemple Creek using the of Estero de San Antonio, was a navigable waterway radioactive fallout 137Cesium (137Cs) dating tech- used to ship produce from the area. Today, the Estero nique. Using 137Cs, sediment layers deposited in is too shallow for large boats. 1954 and 1964 can be determined and sedimentation During the middle to late 1880s, the land was used rates and patterns can be determined (Ritchie and for growing a wide variety of crops. In the early to McHenry, 1990; Walling and He, 1993; Walling et mid-1900s, potatoes were grown extensively. Farming al., 1999). over the last 50 years has evolved to primarily dairy operations and grazing of sheep, beef cattle, and replacement dairy heifers. Grazing pressure has been 2. Study area reduced from historic high levels; but where animals are concentrated for extended periods or where soils 2.1. Setting and landscape are wet, livestock continue to cause erosion problems. This is more prominent in the upper flood plain Stemple Creek Watershed is located in Marin and reaches of the watershed. Restoration and conserva- Sonoma Counties on the northern California coast and tion efforts are underway by landowners on the covers 134 km2. Stemple Creek flows from east to watershed. The Marin and Southern Sonoma County west into the Estero de San Antonio and ultimately Resource Conservation Districts and landowners have flows into Bodega Bay and the Pacific Ocean. Stem- completed 13 km of riparian restoration projects in the ple Creek Watershed is characterized by rolling coast- last 10 years along the waterways. The U.S. Depart- al hills with slopes averaging about 30%. Elevations ment of Agriculture (USDA), National Resource range from sea level at the mouth of the Estero de San Conservation Service (NRCS) approved 24 Environ- Antonio to 100 m at the eastern end of the watershed, mental Quality Incentives Program (EQIP) contracts 200 m along the northern boundary, and 260 m along to improve conservation of the land within the water- the southern boundary. shed between 1997 and 2002. Two geologic formations, the Franciscan and Wil- This history of land use impacting erosion is son Grove, underlie the watershed. The Franciscan superimposed on the geological controls of erosion formation of Mesozoic age is the older and consists of and sedimentation. The Stemple Creek Watershed is a a mixture of rock masses in a sheared, shaley matrix truncated watershed. Travis (1952) reported that the and is fractured and faulted. These rocks are found watershed of Stemple Creek formerly extended to mostly at lower elevations and in the western end of Santa Rosa Mountain. As a larger stream, Stemple the watershed. The Wilson Grove formation is of Creek was able to keep pace with tectonic uplift and Pliocene age and is mostly marine sediments consist- incised a deep sinuous canyon in the coastal hills ing of sandstones, conglomerates, limestone concre- before discharging to the Pacific Ocean. Later tectonic tions, and tuffs. These rocks make up the largest part uplift occurring inland truncated the drainage (Pru- of the watershed. They are found at higher elevations ARTICLE IN PRESS J.C. Ritchie et al. / Geomorphology xx (2004) xxx–xxx 3 and are generally in the eastern end of the watershed fescue [Festuca rubra L. subsp. rubra]. The major (NRCS, 2002). shrub species are coyote brush [Baccharis pilularis Upland hillsides bordering Stemple Creek to a DC.] with significant amounts of poison oak [Toxico- point roughly 2 km from the mouth of the Estero odendron diversilobum (Torr. & A. Gray) Greene], de San Antonio provide a combination of varied and lupine [Lupinus spp.], and blackberry [Rubus spp.]. relatively undisturbed landscape. The stream in this Native woodlands are confined to the upper water- area has fjord-like qualities of steep and twisting shed, especially the north-facing slopes, and along uplands as the dominating characteristic. The inter- streams as riparian zones. These vegetation types spersion of coastal prairie, coastal scrub, riparian formed a mosaic, which was very stable over time ravines and seeps, coastal strand, and grassland in until agriculture was introduced. Several native plant the area creates high habitat value for wildlife. In species that are uncommon or that reach the southern addition, restricted public access has left these areas most limit of their distribution in this area are locally relatively undisturbed, further enhancing their attrac- common in the coastal prairie. These include the tiveness to wildlife. Numerous freshwater seeps oc- native perennial grasses: California fescue [Festuca cur along the hillsides of Estero de San Antonio. californica Vasey], Pacific reed grass [Calamagrostis Along with the numerous riparian ravines, these nutkaensis (J. Presl & C. Presl) Steud.], tufted hair- moist areas increase vegetational diversity and bio- grass [Deschampsia cespitosa (L.) P. Beauv.], Oregon mass and provide valuable wildlife habitat in the dry gentian [Gentiana affinis Griseb. var. ovata A. Gray] upland areas. The watershed includes 1860 ha of and pickleweed [Salicornia europaea L.]. Swamp farmland located in the valley bottoms near the thistle [Cirsium douglasii DC. var. breweri (A. Gray) streams (NRCS, 2002). Keil & C. Turner], known from only one other spot in Mean annual precipitation ranges from 710 mm in Marin County, occurs in the seep areas along the the east to 915 mm in the west, with an average of 760 lower parts of the watershed (CAFG, 1977).