A Stream Restoration Case Study in the California Central Coast

Transcription

1 International Erosion Control Association Annual Conference 2009, Reno, Nevada Case Study Technical Presentation A Stream Restoration Case Study in the California Central Coast Justin S. Rogers, P.E., CFM; Water Resources Project Engineer HDR Engineering, Inc., 8690 Balboa Avenue, Suite 200, San Diego, California, Ph , Fax , justin.rogers@hdrinc.com Brian J. Doeing, P.E., CPESC; National Technical Advisor for Sediment Transport and Scour HDR Engineering, Inc., 8690 Balboa Avenue, Suite 200, San Diego, California, Ph , Fax , brian.doeing@hdrinc.com Biographical Sketches: Justin Rogers is currently a Water Resources Engineer at HDR Engineering in San Diego, and is a Certified Floodplain Manager (CFM) and a registered professional Civil Engineer in California. He received his masters in Environmental Fluid Mechanics from the University of Wisconsin-Madison and his primary interests include hydrology, hydraulic modeling, fluvial geomorphology and stream restoration. He is the author of several publications on the hydrology, and sediment transport in wetlands. Brian Doeing is the National Technical Advisor for Sediment Transport and Scour for HDR Engineering. He brings over 25 years of experience in water resources engineering, and specializes in the areas of sediment transport, stream stability and scour countermeasure design. He is the author of several papers on hydrology, hydraulics, sedimentation, and the evaluation of scour at pipeline stream crossings. He is a Certified Professional in Erosion and Sediment Control (CPESC), a registered professional Civil Engineer in the states of California and Nevada, and received a Masters in Civil Engineering from San Diego State. Abstract: San Antonio Creek is located in the California central coast area within Vandenberg Air Force Base. The creek is actively adjusting its profile and channel geometry and has experienced significant erosion (degradation), deposition (aggradation), channel widening, and bend migration during the recent past. The results of several studies indicate that this trend is expected to continue. The effects of this instability have led to a degraded stream channel environment and hydrologic disconnection of the stream from the surrounding floodplain. In addition to the loss of habitat and wetlands, local infrastructure, such as utilities and highways, and cultural resources are threatened. The purpose of this project was to design scour protection for the infrastructure and to restore form and function to San Antonio Creek within the project area. HDR worked in conjunction with the U.S. Air Force, U.S. Army Corps of Engineers, David Derrick (USACE Waterways Experiment Station), John McCullah (Salix Earthcare), and others to develop a proposed design. The proposed design incorporates seven rock riffle grade control structures that will mitigate the lowering of the channel, provide pool and riffle features, and also provide for fish passage. Additionally, bank toe and slope protection will be provided at key areas. Habitat will be restored with the use of environmentally sensitive streambank stabilization and restoration methods. This is expected to provide enhanced habitat for several endangered species within the creek as well as other species. Additionally, cutting point bars and reshaping the channel will allow for a more natural channel shape with a restored flood terrace. Key Words: Stream Restoration, Bank Revetment, Bioengineering, Grade Control, Scour Marketing Paragraph: This case study presentation will focus on the stream restoration design methods used for a severely degraded stream in the Central Coast of California. Design of rock grade control structures, bank revetments and habitat restoration will be discussed.

2 Synopsis 1.0 Introduction San Antonio Creek is located in the California central coast area within Vandenberg Air Force Base (Figure 1). The creek is actively adjusting its profile and channel geometry (Figure 2) and has experienced significant erosion (degradation), deposition (aggradation), channel widening, and bend migration during the recent past. The results of several studies indicate that this trend is expected to continue. The effects of this instability have led to a degraded stream channel environment and hydrologic disconnection of the stream from the surrounding floodplain. In addition to the loss of habitat and wetlands, local infrastructure, such as utilities and highways, and cultural resources are threatened at 3 sites (Figure 3). The key concerns at the site were over-steepened banks and severe head cuts in the channel. Additionally there were environmental concerns with California red legged frog, three-spine stickleback fish, and steelhead trout. Figure 1: Project Location The purpose of this project was to design scour protection for the infrastructure and to restore form and function to San Antonio Creek within the project area. HDR worked in conjunction with the U.S. Air Force, U.S. Army Corps of Engineers, David Derrick (USACE Waterways Experiment Station), John McCullah (Salix Earthcare), and others to develop a proposed design. The project approach was to first conduct a field investigation and to compare current and historical topography. Geomorphic, hydrology, and hydraulic analyses were also conducted. The geomorphic analysis indicated that the channel could be expected to continue degrading, and the channel would at some point transition to a widening phase. The hydraulic analysis indicated that flow depths for the 100- year event were in the range of 10 to 22 feet deep, flowing at 9 to 24 feet per second. The 100-year discharge is completely confined within the main channel in the project reach. Based on this collection of site information, the restoration design was initiated.

3 Figure 2: Profile in 1993 (green), 2005 (black) and 2007 (red) Figure 3: Project Overview 2.0 Design The overall design approach was to mitigate the channel degradation using rock grade control structures. The general (bend) scour at the three sites where local infrastructure was threatened would be mitigated using bank revetment. The grade control structures and revetments would all be designed for the 100- year event. The project would incorporate bioengineering, including pole plantings and seeding, into the design to restore habitat in the stream as much as possible. The overall goal was to restore the form and function to the creek. The rock riffle design was the key protection feature. Fish passage needed to be maintained within the system, so hand-formed step pools will be constructed on the 20:1 slope on the grade control. Sizing of the rock for the grade control structures was conducted using several design methods. These included: Isbash (1937), USBR (Peterka, 1958), ARS Rock Chute (Robinson et al., 1998), Abt and Johnson (1991), USACE Steep Slope (EM 1601). These methods are all summarized in Rock Ramp Design Guidelines

4 (USBR, 2007). The methods were compared and the average of the methods times a factor of safety was used for design. Alternately, the maximum method could be selected. The results indicated 2-ton and 4- ton rock for some structures, with 8-ton rock used for the highest energy locations (Caltrans riprap specification). Calculation of the local scour at the toe of grade control structures was based on Clark County (1999) guidelines. This manual recommends using the Simons and Li (1986) for the submerged weir crest case, and the minimum of Simons and Li (1986) or the Veronese (1937) for un-submerged case. Additionally the long term scour was based on a profile analysis. To accommodate this expected scour, launching rock was placed at the toe of the structure with an equivalent volume to launch to the scour depth. The overall detail is shown in Figure 4. Cross Section Plan Profile Figure 4: Grade Control Detail The design of the bank protection incorporated a terraced floodplain concept to widen the incised channel and reduce some of the hydraulic energy. A variety of protection methods were used including vegetated rock riprap, vegetated mechanically stabilized earth, longitudinal peak stone toe, and brush layering. Bend scour was estimated using the Maynord (1996) method, and long term scour was estimated by profile analysis. Toe launching rock was designed to accommodate the calculated scour depths. Rock sizing was conducted using the USACE Engineering Manual 1601 (USACE, 1994). This method was found to be most reliable for revetment design in recent research from the Transportation Research Board (NCHRP, 2006). Site 1 design included rock protection to the 100-year event, launching rock, willow plantings, and a terraced floodplain on the inside of the bend (Figure 5). Site 2 included a launching rock toe, upper protection using vegetated mechanically stabilized earth, and a two-level terraced floodplain on the inside of the bend (Figure 6). Site 3 included longitudinal peak stone toe protection with backfill and willow plantings (Figure 7). Bioengineering for the site primarily consisted of willow plantings into the designed riprap protection. These willows will be harvested onsite, and the primary design guideline is that they must have a moisture source and available soil. The disturbed soil areas will be reseeded with a specific seed mix for

5 the creek side and the upper slope areas using local native seeds. Additional references for design can be found in Fischenich (2001), and ESSenS (2004). Figure 5: Site 1 Design Figure 6: Site 2 Design Figure 7: Site 3 Design

6 3.0 Conclusions The proposed design incorporates seven rock riffle grade control structures that will mitigate the lowering of the channel, provide pool and riffle features, and also provide for fish passage. Additionally, bank toe and slope protection will be provided at key areas. Habitat will be restored with the use of environmentally sensitive streambank stabilization and restoration methods. This is expected to provide enhanced habitat for several endangered species within the creek as well as other species. Additionally, cutting point bars and reshaping the channel will allow for a more natural channel shape with a restored flood terrace. A key point is that the design is for 100-year level of protection for the infrastructure but also includes bioengineering features to improve habitat. One of the key lessons learned during this project was that engineering and environmental goals can both be achieved. However, this is only possible if frequent and direct communication is kept open between the design team, client, and regulators. A second key lesson is that bioengineering design methods are currently not well known especially for high energy conditions. More research is needed in this area. A third lesson is that designing with rock under high energy conditions requires careful consideration of failure mechanisms. And finally, good designers must consider constructibility and apply general concepts to site-specific characteristics Acknowledgments Michael Bird, U.S. Air Force, Vandenberg Air Force Base; David Derrick, U.S. Army Corps of Engineers Waterways Experiment Station; John McCullah, Salix Earthcare, Inc.; Jon Blanchard, Fugro West, Inc.; Sunit Deo, HDR Engineering, Inc.; Garrett Higerd, Mono County (formerly w/ HDR Engineering, Inc.) 5.0 References Abt, S.R., and T.L. Johnson Riprap design for overtopping flow. J. of Hydraulic Eng., Amer. Soc. of Civil Eng. 117(8): Clark County Flood Control Manual, for Clark County, Nevada. Fischenich, Stability Thresholds for Stream Restoration Materials, ERDC. Isbash, S Construction of dams by depositing rock in running water, Communication No. 3, 2nd Congress on Large Dams. Washington, DC. pp Maynord, S.T Toe-Scour Estimation in Stabilized Bendways, J. of Hydraulic Engineering, p National Cooperative Highway Research Program (NCHRP), Riprap Design Criteria, Recommended Specifications, and Quality Control. Report 568. Peterka, A.J Hydraulic design of stilling basins and energy dissipators. U.S. Dept. of the Interior, Bureau of Reclamation, Engineering Monograph No. 25. Robinson, K.M., C.E. Rice, and K.C. Kadavy Design of rock chutes. Trans. of the Amer. Soc. of Agric. Eng. 41(3): Salix, Inc., ESSenS Environmentally Sensitive Streambank Stabilization, 2004 Simons, Li and Associates Hydraulic Model Study of Local Scour Downstream of Rigid Grade- Control Structures. Pima County, Arizona. U.S. Army Corps of Engineers (USACE) EM Hydraulic Design of Flood Control Channels. Veronese, A Erosioni di fondo a valle di uno scarico. Annali dei Lavori Publicci. 75(9), (in Italian). U.S. Bureau of Reclamation (USBR) 2007, Rock Ramp Design Guidelines.