Santa Maria Valley Watershed Characterization for Hydromodification Management Within the City of Santa Maria September 7, 2010 Tetra Tech City of Santa Maria Utilities Department 3201 Airpark Dr. Suite 108 2065 E. Main St. Santa Maria, CA 93455 Santa Maria, CA 93454 Santa Maria Valley Watershed Characterization for Hydromodification Management within the City of Santa Maria Contents 1. INTRODUCTION ................................................................................................................... 1 1.1. Problem Statement ......................................................................................................... 1 1.2. City of Santa Maria Goals and Objectives ...................................................................... 1 1.3. Scope of Report.............................................................................................................. 2 1.4. Hydromodification Management Plan Background ........................................................ 2 1.4.1. Regulatory Background .......................................................................................... 2 1.4.2. Hydromodification Management Requirements ...................................................... 3 1.4.3. Joint Effort Process and Participation ..................................................................... 5 2. LITERATURE REVIEW AND DATA AVAILABILITY ........................................................... 6 2.1. Data Inventory ................................................................................................................ 6 2.2. Hydromodification Control Criteria Development ........................................................... 7 3. WATERSHED CHARACTERIZATION ................................................................................. 9 3.1. General Information ........................................................................................................ 9 3.1.1. Study Area ........................................................................................................................... 10 3.1.2. Topography ........................................................................................................... 11 3.1.3. Land Use .............................................................................................................. 13 3.1.4. Soils ...................................................................................................................... 16 3.1.5. Climate .................................................................................................................. 18 3.1.6. Groundwater ......................................................................................................... 22 3.1.7. Surface Waters and Subwatersheds .................................................................... 29 3.1.8. Runoff Flow ........................................................................................................... 37 3.2. Water Quality Challenges ............................................................................................. 39 3.2.1. Surface Water Impairments .................................................................................. 39 3.2.2. Groundwater Impairments .................................................................................... 40 4. CONCLUSIONS .................................................................................................................. 41 4.1. Summary of Observations ............................................................................................ 41 4.2. Recommendations ........................................................................................................ 42 4.2.1. Monitoring ............................................................................................................. 42 4.2.2. Quantify Basin Impacts ......................................................................................... 43 4.2.3. Possible Joint Effort Support ................................................................................ 43 5. REFERENCES .................................................................................................................... 44 APPENDICES A Field Reconnaissance of Channels in the City of Santa Maria i Santa Maria Valley Watershed Characterization for Hydromodification Management within the City of Santa Maria Tables Table 1. Summary of Data Types and Source .............................................................................................. 6 Table 2. Summary of Land Use within Study Area ...................................................................................... 14 Table 3. Characteristics of the USDA-NRCS soil groups ............................................................................ 17 Table 4. Percent Breakdown of Soil Groups in Study Area......................................................................... 17 Table 5. Monthly Average Evapotranspiration Rates (inches) .................................................................... 21 Table 6. Average Monthly Evaporation Rates (inches/day) ........................................................................ 22 Table 7. Summary of Water Requirements and Supplies for the City (AFY) .............................................. 24 Table 8. USGS DTW Measurements (February 2010) ............................................................................... 27 Table 9. City of Santa Maria Landfill Min. and Max. .................................................................................... 28 Table 10. USGS Gauging Stations in the Santa Maria Watershed ............................................................. 38 Table 11. CCAMP Monitoring Sites ............................................................................................................. 39 Table 12. Summary of Waterbody Impairments in the City of Santa Maria and the Santa Maria River ..... 39 Figures Figure 1. Santa Maria River Watershed. ..................................................................................... 10 Figure 2. Study Area. .................................................................................................................. 11 Figure 3. Santa Maria Watershed Topography (Hillshade). ........................................................ 12 Figure 4. Parcel Land Use Within Study Area. ........................................................................... 15 Figure 5. Percent Impervious Cover. .......................................................................................... 16 Figure 6. Hydrologic Soil Groups Within Study Area. ................................................................. 18 Figure 7. NCDC Weather Stations and SBC Rain Gauges. ....................................................... 19 Figure 8. Monthly Average Evaporation Rates. .......................................................................... 22 Figure 9. City of Santa Maria Domestic Supply Wells and USGS Monitoring Wells. .................. 25 Figure 10. Landfill Groundwater Monitoring Wells. ..................................................................... 26 Figure 11. Natural Drainages and Susceptibility to Hydromodification ....................................... 31 Figure 12. Surveyed Riparian Habitat. ........................................................................................ 32 Figure 13. City Watersheds and Discharge Points. .................................................................... 33 Figure 14. Retention and Detention Basins. ............................................................................... 36 Figure 15. USGS Gauging Station Locations. ............................................................................ 38 ii Santa Maria Valley Watershed Characterization for Hydromodification Management within the City of Santa Maria 1. INTRODUCTION 1.1. Problem Statement As urban and agricultural development occur throughout the Central Coast, local landscapes and hydrology are altered by buildings, roads, lawns, landscaping, and parking lots. Those development activities can substantially change site hydrology by covering pervious surfaces (e.g., vegetated areas, natural soils) with impervious surfaces (e.g., roofs, pavement). Additionally, the ability of the landscape to absorb water during storms is reduced by soil compaction during construction and landscaping. As a result, the volume, rate, and frequency of storm water runoff from these sites can increase dramatically, greatly altering key natural hydrologic processes, such as surface runoff, sediment and pollutant transport, groundwater recharge, and evapotranspiration. Such changes in hydrologic process resulting from land development collectively are called hydrologic modification, or hydromodification, which the U.S. Environmental Protection Agency (EPA) defines as, “The alteration of the natural circulation or distribution of water by the placement of structures or other activities” (USEPA 1992). Hydromodification is also an umbrella term for those modifications of the natural water cycle resulting from urbanization, agriculture, and altered drainage patterns that have the potential to affect surface and groundwater resources adversely in a number of ways, such as increasing pollutant loads, reducing groundwater infiltration, or physically altering receiving waters and drainages. Although the hydrologic contributions of an individual site might seem insignificant