Climate Change and Groundwater Sustainability in a Mixed Agriculture/Urban Basin

Transcription

1 Amec Foster Wheeler 2017

2 Climate Change and Groundwater Sustainability in a Mixed Agriculture/Urban Basin Isabella Polenghi-Gross, PhD; Matt Baillie, CHg, and Les Chau, BCES Amec Foster Wheeler Environment and Infrastructure, Inc. 09/19/17 Amec Foster Wheeler 2017

3 Background Our team has been working on groundwater sustainability projects in Monterey County for 15+ years: Monitoring network sufficiency study: 1999 Hydrogeologic assessment of the northern part of the county: 2004 State of the Basin report: 2015 Hydrogeologic modeling for the Interlake Tunnel Construction Project for MCWRA: 2017 Monterey County Image Source: Wikipedia

4 Outline 1. Objectives of the Project 2. Agricultural Resiliency 3. Salinas Basin 4. Salinas Basin Issues 5. Approach to Address Issues (SVIHM) 6. Incorporation of climate change variables in SVIHM 7. Conclusions

5 Project Objectives To determine whether or not current water supplies are sufficient to meet water demand To investigate the effects of climate change on the County water supplies To evaluate the ability of various County projects and initiatives to increase water supplies. Image Source: Monterey County Farm Bureau

6 Ag Resiliency Uncertainty in future climate conditions affect agriculture. How will future conditions affect agricultural demand? If demand increases, and storage decreases, how will that demand be met? Agriculture needs to be resilient to ensure future sustenance California has the 7th largest economy in the world Ag is a $54 billion industry Image Source: Monterey County Farm Bureau

7 Sustainable Groundwater Management Act Long over due senate bills passed in 2014 by California Legislature, mandating that groundwater basins must reach sustainable management by 2042 Gives responsibility for planning and managing for sustainability to local agencies Sustainability is defined based on avoiding undesirable results : 1. Lowering of groundwater levels 2. Reductions in groundwater storage 3. Seawater intrusion 4. Degradation of water quality 5. Land subsidence 6. Depletion of surface water impacting beneficial uses

8 Climate Change Effects on Ag Demand Increased temperature; lengthened growing season; increased precipitation variability; increased potential evapotranspiration. Result is increased overall demand for groundwater and increased uncertainty of supply. While agriculture will likely require more water supply, surface water supplies are likely to become less plentiful, sporadic, and less reliable unless big changes are made in water resource management and irrigation practices. Source: USDA;

9 Salinas Valley (Steinbeck's East of Eden) California largest Coastal Basin Drains by the Salinas River, overlies four hydrologically interconnected units, and operates two surface reservoirs Annual precipitation averages between 10 to 16 inches/year Heavily agricultural basin, strongly depends on GW Numerous water-related issues Includes a few of the highest at-risk basins in California Carmel Valley Source: California Department of Water Resources

10 Water Resources Source: California Water Plan

11 Salinas Basin Issues (today) Seawater intrusion Groundwater overdraft Falling water levels Groundwater storage depletion Water quality degradation Continued streamflow losses

12 Extent of Seawater Intrusion Source: Monterey County Water Resources Agency

13 Groundwater Storage Depletion Drought Source: Brown and Caldwell

14 Falling Groundwater Elevations Reversal of GW Gradient and Degradation of Water Quality Seawater has the potential to intrude this whole area and more Reversal of flow away from the ocean, limits flushing of undesirable constituents in groundwater. Accumulation of nitrate and salts (TDS) is the result of falling groundwater elevations and the reversal of groundwater gradient Source: Monterey County Water Resources Agency

15 Approach to Address Issues MCWRA s mandate is to determine whether water supplies are sufficient to meet demands under future conditions of land use, climate, population, etc. They are not a policy making body Update sustainability plans best water resource management practices, and more efficient irrigation. Use of computer models to accurately predict the effects of climate changes, water supply, and demand

16 Salinas Valley Integrated Hydrologic Model (SVIHM) Groundwater and surface water flow integrated into a single model. Groundwater-surface water model (in MODFLOW-OWHM) is coupled to a watershed model (in HSPF) that simulates the generation of runoff. Historical model that simulates conditions from 1967 to 2014 The model is calibrated to groundwater levels, streamflow, and agricultural pumpage.

17 Schematic of model inputs and observations for SVIHM

18 SVIHM model boundaries

19 Incorporating Climate Change into SVIHM Pertinent climate variables: precipitation, temperature, evapotranspiration (ET), and sea level The SVIHM simulates the interactions of the following: Climate change variables (GCMs); Groundwater levels and storage; Surface water flow and flooding; Land use (agriculture and urban consumptive uses); Reservoir operations for water releases to the Salinas River, flood control, groundwater replenishment, and irrigation practices.

20 Collaboration with USGS USGS built and calibrated the SVIHM simulates the groundwater and surface water systems as well as the reservoirs and dynamic agricultural demand Amec Foster Wheeler works with the USGS to configure the future simulations, and to identify the climate future conditions input datafiles based on the selected futures from climate models Run the future simulations

21 Summary MCWRA approach towards resilience and sustainability involves: Looking at existing infrastructures and adaptively managing them to mitigate the effects of climate change on their water supplies; Implementing BMPs and efficient irrigation practices Using integrated numerical models to predict future supply and demand of water to maintain sustainable use of surface water and ground water; To examine operational parameters of reservoirs to assure the public that their water supply and infrastructure are reliable.

22 From Steinbeck's East of Eden I have spoken of the rich years when the rainfall was plentiful. But there were dry years too, and they put a terror on the valley. The water came in a thirty-year cycle. There would be five or six wet and wonderful years when there might be nineteen to twenty-five inches of rain, and the land would shout with grass. Then would come six or seven pretty good years of twelve to sixteen inches of rain. And then the dry years would come, and sometimes there would be only seven or eight inches of rain. The land dried up and the grasses headed out miserably a few inches high and great bare scabby places appeared in the valley. The live oaks got a crusty look and the sage-brush was gray. The land cracked and the springs dried up and the cattle listlessly nibbled dry twigs. Then the farmers and the ranchers would be filled with disgust for the Salinas Valley. The cows would grow thin and sometimes starve to death. People would have to haul water in barrels to their farms just for drinking. Some families would sell out for nearly nothing and move away. And it never failed that during the dry years the people forgot about the rich years, and during the wet years they lost all memory of the dry years. It was always that way. Thank you!