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Auburn Ravine-Hemphill Diversion Assessment Sediment Transport Study

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Auburn Ravine-Hemphill Diversion Assessment Sediment Transport Study Auburn Ravine-Hemphill Diversion Assessment Sediment Transport Study Prepared for: Nevada Irrigation District Prepared by: June 2020 AUBURN RAVINE-HEMPHILL DIVERSION ASSESSMENT SEDIMENT TRANSPORT STUDY June 1, 2020 A REPORT PREPARED FOR: Tonia M. Tabucchi Herrera, P.E. Nevada Irrigation District 1036 West Main Street Grass Valley, California 95945 [email protected] by Kealie Pretzlav, PhD Geomorphologist/Hydrologist Exp. 8/31/20 David Shaw, P.G. Principal Geomorphologist/Hydrologist © 2020 Balance Hydrologics, Inc. Project Assignment: 220031 800 Bancroft Way, Suite 101 ~ Berkeley, California 94710-2251 ~ (510) 704-1000 ~ [email protected] Balance Hydrologics, Inc. i AUBURN RAVINE-HEMPHILL DIVERSION ASSESSMENT SEDIMENT TRANSPORT STUDY < This page intentionally left blank > ii Balance Hydrologics, Inc. AUBURN RAVINE-HEMPHILL DIVERSION ASSESSMENT SEDIMENT TRANSPORT STUDY TABLE OF CONTENTS 1 INTRODUCTION 1 2 SITE BACKGROUND 3 2.1 Site Location 3 2.2 Soils 4 2.3 Geology 5 2.4 Geomorphic Observations 5 3 MODELING METHODOLOGY 10 3.1 Input Design Storm Hydrographs 10 3.1.1 Design Storms and Rainfall 10 3.1.2 Watershed Characteristics 11 3.1.3 Hydrograph Parameterization and Model Calibration 11 3.2 Model Domain Mesh 13 3.3 Bedload Transport Function 14 3.4 Channel Grain Size Distributions 15 3.5 Channel Bed Erodibility 16 3.6 Channel Roughness 16 3.7 Active Layer Depth 17 3.8 Upstream Boundary Conditions 17 3.9 Downstream Boundary Conditions 18 3.10 Model Representation of Alternatives 18 3.10.1 No Action 19 3.10.2 Alternative 1: Dam Removal and No Sediment Management 19 3.10.3 Alternative 2: Dam Removal and Sediment Management 19 3.10.4 Alternative 3: Incremental Dam Removal and No Sediment Management 20 4 MODELING RESULTS 21 4.1 No Action 21 4.2 Alternative 1: Dam Removal and No Sediment Management 22 4.3 Alternative 2: Dam Removal and Sediment Management 22 4.4 Alternative 3: Incremental Dam Removal 23 5 NEXT STEPS 25 5.1 Model Refinement 25 5.2 Use of Design Storms for Understanding Geomorphic Response Times 25 Balance Hydrologics, Inc. iii AUBURN RAVINE-HEMPHILL DIVERSION ASSESSMENT SEDIMENT TRANSPORT STUDY 5.3 Upstream Bank Stability Assessment 25 5.4 Fish Habitat Impacts 26 6 LIMITATIONS 27 7 REFERENCES 28 iv Balance Hydrologics, Inc. AUBURN RAVINE-HEMPHILL DIVERSION ASSESSMENT SEDIMENT TRANSPORT STUDY LIST OF TABLES Table 3-1 Precipitation depths scaled to 800 feet elevation 10 Table 3-2 Peak design flows (Gotvald, 2012) and calibrated lag time values 12 LIST OF FIGURES Figure 2-1 Site location overview map. 3 Figure 2-2 Contributing watershed for Auburn Ravine at Hemphill Diversion Dam. 4 Figure 2-3 Geomorphic units. 6 Figure 2-4 Example of outcropping bedrock and sand and gravel bar, located upstream of Hemphill Dam, looking upstream. 7 Figure 2-5 Channel thalweg elevation within the model domain. 8 Figure 2-6 Aerial images of upstream model boundary comparing May 2002, June 2011, September 2019. 9 Figure 3-1 Design storms for the 2-, 10-, and 25-year event. 12 Figure 3-2 Preliminary pilot channel orientation used in the Sediment Management Alternative (Alt. 2). 14 Figure 3-3 Modeled surface and subsurface grain size distributions (GSD) (left), and modeled grain size bins (right). 15 Figure 3-4 Erodible and non-erodible areas in the No Sediment Management alternative (Alternative 1). 16 Figure 3-5 Input sediment rating curves for each grain size bin. 18 Figure 3-6 Downstream hydraulic rating curve. 19 APPENDICES Appendix A Modeling Results Balance Hydrologics, Inc. v AUBURN RAVINE-HEMPHILL DIVERSION ASSESSMENT SEDIMENT TRANSPORT STUDY < This page intentionally left blank > vi Balance Hydrologics, Inc. AUBURN RAVINE-HEMPHILL DIVERSION ASSESSMENT SEDIMENT TRANSPORT STUDY 1 INTRODUCTION The Hemphill Diversion Dam provides infrastructure for maintaining agricultural irrigation delivery of Nevada Irrigation District (NID) imported water from Auburn Ravine. Auburn Ravine is one of the many tributaries to the Feather River, and subsequently the Sacramento River, which has been identified by the Central Valley Steelhead Draft Recovery Plan (NMFS, 2009) as a good candidate for habitat restoration. Additionally, Auburn Ravine supports chinook salmon as indicated in recent studies by California Department of Fish and Wildlife, Placer County and NMFS. The current Hemphill Diversion Dam is a fish passage barrier and removing it would add approximately 6 additional miles of headwater habitat for Steelhead and Chinook Salmon. Nevada Irrigation District (NID) has requested that Balance Hydrologics (‘Balance’) characterize the nature of channel bed evolution and sediment transport, as associated with different dam removal alternatives. We understand that NID is still in the process of evaluating and selecting a preferred alternative, a process which involves many components including diversion replacement alternatives, fish count surveys, and evaluation and documentation of environmental impacts, as required under CEQA. This report is limited to a sediment transport modeling study, intended to characterize how sediment transport and channel evolution may be affected by three general dam removal alternatives. The modeled alternatives are not necessarily those that will ultimately be considered through CEQA, but are developed to represent the range of probable sediment transport response associated with different dam removal scenarios: . Alternative 1: Dam removal and no active sediment management . Alternative 2: Dam removal and active sediment management . Alternative 3: Incremental dam removal and no active sediment management At this time, we understand that the general project alternatives being considered fall into one of these categories with respect to sediment transport and we have limited our analysis to these three alternatives for clarity and simplicity. Each sediment transport alternative can ultimately be compared to the “No Action” scenario which is run as an existing conditions scenario, which was also used to help parameterize the sediment transport model. Balance Hydrologics, Inc. 1 AUBURN RAVINE-HEMPHILL DIVERSION ASSESSMENT SEDIMENT TRANSPORT STUDY For the purposes of this study, “Dam removal” means complete removal of hardened structures within the active channel area, including the bed and bank protection rip rap around the dam. “Incremental dam removal” refers to removal of the dam incrementally over three different construction seasons. Due to the nature of the numerical model as outlined below, we have modeled incremental dam removal of the approximately 8-foot-high dam as follows: - Step 1: Removal of 2 feet of dam - Step 2: Removal of 5 total feet of dam - Step 3: Removal of all 8 feet of the dam; this is the same as Alt. 1 and so not modeled separate (see below) “Active sediment management” refers to excavating and grading the impounded deposits into a designed quasi-stable position to limit the total volume of sediment released to downstream areas. We have modeled one generalized channel configuration for this purpose, but more detailed design work would be required before implementing that alternative, especially in light of the unstable streambanks upstream of the dam. Alternatives 1 and 3 (no active sediment management) involve removing all or part of the dam and letting natural sediment production and transport processes evolve the channel as flow capacity allows. This study was carried out to evaluate each alternative in terms of the following questions and geomorphological impacts: 1. What flow magnitudes and durations are required for the channel to return to a state of quasi-stable equilibrium after implementing each alternative? 2. What is the potential for erosion and deposition within the model domain? The general benefits and limitations of each alternative are discussed from a geomorphological perspective, but we have not included potential short- or long-term impacts to fish habitat as a result of the introduction of the impounded sediment downstream. 2 Balance Hydrologics, Inc. AUBURN RAVINE-HEMPHILL DIVERSION ASSESSMENT SEDIMENT TRANSPORT STUDY 2 SITE BACKGROUND 2.1 Site Location The Hemphill Diversion Dam is located on Auburn Ravine approximately 2 miles east of Lincoln, California in Placer County (Figure 2-1). The project site is located just north of the Turkey Creek Golf Club and accessed from Virginiatown Road. The contributing watershed is approximately 25.9 square miles with the headwaters originating at elevation 1687 feet 1 and the project site at 207 feet (Stream Stats, 2020). Average watershed elevation is approximately 840 feet (Figure 2-2). Figure 2-1 Site location overview map. 1 Unless otherwise specified, all elevations in this report are relative to the NAVD 88 vertical datum. Balance Hydrologics, Inc. 3 AUBURN RAVINE-HEMPHILL DIVERSION ASSESSMENT SEDIMENT TRANSPORT STUDY Figure 2-2 Contributing watershed for Auburn Ravine at Hemphill Diversion Dam. The Hemphill Diversion Dam is approximately 8 feet high and constructed out of concrete. During the diversion season, 3-foot flashboards can be installed to increase ponding depths in the impoundment area and direct flow into the Hemphill Canal. An approximately 5-foot-deep scour pool is present on the downstream side of the dam, which is partially armored with placed boulders. The channel banks immediately adjacent to the dam are hardened with boulder rip rap or concrete. 2.2 Soils Soils in the Auburn Ravine watershed are primarily comprised of coarse sandy loam, and silt loam, with approximately 18 percent rock outcrop coverage (NRCS, 2020). The NRCS classifies all soils into one of four Hydrologic Soil Groups (HSG) which denote soil permeability and infiltration rate, ranging from Group A soils with high potential infiltration rates to Group D soils with the lowest potential for infiltration. The Hemphill Diversion Dam 4 Balance Hydrologics, Inc. AUBURN RAVINE-HEMPHILL DIVERSION ASSESSMENT SEDIMENT TRANSPORT STUDY contributing watershed is dominated by type C soils (45%), followed by type D soils (25%), and type B soils (15%). Approximately 15% of the watershed is mapped as Xerorthents, or cut and fill material which has been displaced primarily as the result of mining activity.
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