Tijuana River Valley Needs and Opportunities Assessment – Sediment Technical Memorandum San Diego, California March 13, 2020 Tijuana River Valley Needs and Opportunities Assessment – Sediment Technical Memorandum This page is intentionally blank. March 13, 2020 Tijuana River Valley Needs and Opportunities Assessment – Sediment Technical Memorandum Contents 1 Introduction .......................................................................................................................................... 1 1.1 Background ............................................................................................................................... 1 1.2 Purpose ..................................................................................................................................... 3 2 Review of Existing Projects and Information ....................................................................................... 3 2.1 Tijuana River ............................................................................................................................. 3 2.2 Smuggler’s Gulch ...................................................................................................................... 4 2.3 Goat Canyon ............................................................................................................................. 4 2.4 Yogurt Canyon .......................................................................................................................... 5 3 Priority Issues ...................................................................................................................................... 5 3.1 Sediment Characteristics .......................................................................................................... 6 3.1.1 Tijuana River ................................................................................................................ 6 3.1.2 Smuggler’s Gulch ......................................................................................................... 7 3.1.3 Yogurt Canyon ............................................................................................................. 8 3.2 Contaminants ............................................................................................................................ 8 3.3 Residual Sediments .................................................................................................................. 8 4 Development of Potential Projects ...................................................................................................... 9 4.1 Tijuana River ............................................................................................................................. 9 4.1.1 Projects ...................................................................................................................... 11 4.1.2 Cost ............................................................................................................................ 15 4.2 Smuggler’s Gulch .................................................................................................................... 15 4.2.1 Projects ...................................................................................................................... 20 4.2.2 Cost ............................................................................................................................ 23 4.3 Goat Canyon ........................................................................................................................... 24 4.3.1 Projects ...................................................................................................................... 25 4.3.2 Cost ............................................................................................................................ 26 4.4 Yogurt Canyon ........................................................................................................................ 26 4.4.1 Projects ...................................................................................................................... 28 4.4.2 Cost ............................................................................................................................ 29 4.5 Sediment Management Projects ............................................................................................. 29 4.5.1 Goat Canyon Sediment Management Project ........................................................... 29 4.5.2 Nelson Sloan Management and Operations Plan ...................................................... 33 4.5.3 Tijuana River Watershed Hydraulics and Hydrology Studies – Phase 2 ................... 35 5 Emergency Action Plan ..................................................................................................................... 36 6 Summary of Project Recommendations ............................................................................................ 36 7 References ........................................................................................................................................ 43 March 13, 2020 | i Tijuana River Valley Needs and Opportunities Assessment – Sediment Technical Memorandum Tables Table 1. Tijuana River Sediment Inflow Load ............................................................................................... 6 Table 2. Smuggler’s Gulch Representative Grain Size Distribution ............................................................. 7 Table 3. Smuggler’s Gulch Peak Discharges ............................................................................................. 16 Table 4. Smuggler’s Gulch Sediment Transport Results ............................................................................ 21 Table 5. Historical Sediment Excavation .................................................................................................... 23 Table 6. Smuggler’s Gulch Proposed Alternative Cost Estimates .............................................................. 23 Table 7. Grain Size Distribution – Goat Canyon Studies ............................................................................ 25 Table 8. Yogurt Canyon Peak Discharges .................................................................................................. 27 Table 9. Yogurt Canyon Proposed Alternative Cost Estimate .................................................................... 29 Table 10. Unit Cost of Nelson Sloan Quarry Operation .............................................................................. 35 Table 11. Proposed Implementation Projects ............................................................................................. 37 Figures Figure 1. Dry-weather Flow Infrastructure in the Tijuana River .................................................................... 2 Figure 2. Smuggler’s Gulch Sediment Load Rating Curvea .......................................................................... 7 Figure 3. Tijuana River Watershed ............................................................................................................. 10 Figure 4. Tijuana River Study Area ............................................................................................................. 12 Figure 5. Alternative A – In-channel Sedimentation Basins ........................................................................ 13 Figure 6. Alternative B – Off-channel Sedimentation Basin ........................................................................ 14 Figure 7. Alternative C – Combination of In-channel and Off-channel Sedimentation Basins ................... 15 Figure 8. Tijuana River Tributary Canyons ................................................................................................. 16 Figure 9. Smuggler’s Gulch Hydrographs ................................................................................................... 17 Figure 10. Smuggler’s Gulch Field Photos ................................................................................................. 18 Figure 11. Smuggler’s Gulch 5-year Floodplain.......................................................................................... 19 Figure 12. Smuggler’s Gulch HEC-RAS Model Schematic ........................................................................ 20 Figure 13. Goat Canyon Sedimentation Basins .......................................................................................... 26 Figure 14. Yogurt Canyon 5-year Floodplain .............................................................................................. 27 Figure 15. Yogurt Canyon HEC-RAS Model Schematic ............................................................................. 28 Figure 16. Yogurt Canyon Pilot Channel .................................................................................................... 29 Figure 17. Goat Canyon Sediment Management Plan ............................................................................... 30 Figure 18. Proposed Deposited Sand Beach Work Zone ........................................................................... 32 Figure 19. Nelson Sloan Quarry Location ................................................................................................... 34 Appendices Appendix A. Hydraulic Results ................................................................................................................... A-1 Appendix B. Sediment Transport Results .................................................................................................