Water Management Options Analysis Sonoma Valley Model Results Sonoma Valley Technical Work Group October 8, /08/2007

Sonoma Valley Model Results 6,000 to 8,500 AFY demand increase 17,300 AF decrease in storage Localized groundwater declines Limitations – Model does not Adequately represent basin complexities Model salinity intrusion Include accurate groundwater production Include adequate surface water flow data Consider seasonal variations Model Use Provides a tool for assessing conceptual water management options

Reference: USGS SIR Sonoma Valley Groundwater Demand

Notes: SW – surface water GW – groundwater AF – acre-feet References: USGS, 2006 for estimates of domestic and agricultural groundwater use City of Sonoma and Valley of the Moon Water District 2005 Urban Water Management Plans for estimates of urban groundwater use (Brown & Caldwell, February and August 2007). Total Water Use Groundwater Use Year 2000

How was the Model used? Simulation of a complex subsurface system Simulation of the groundwater budget for the Sonoma Valley basin over Evaluation of 12 separate simulations, combining four water management options and two scenarios under varying hydrologic conditions The model, in its current state, has limitations but is suitable for this type of narrow analysis

Inactive cells General Head boundary Drain boundary 13 X 33 mile area 133 rows 52 columns General head boundary south bay Drain boundary layer 1 Model set up

Model Subsurface Properties

Recharge Zones and Stream Boundary in Layer 1

Location of Pumping Wells in the Model Model Agricultural Wells Model Private Domestic Wells Model Urban Supply Wells (City of Sonoma) Model Urban Supply Wells (Valley of the Moon Water District) Note:Locations shown are approximate. Model wells are shown at the center of the grid cell to which they are assigned. Some grid cells contain multiple wells Reference:Map from USGS, 2006.

A,B,C,D D-6 No Additional Imported Water Beyond Existing Water Rights Model Cases Normal Year Multiple Dry Year Additional Imported Water No Additional Imported Water Beyond Existing Water Rights No Additional Action N-0 A (Storm Water Recharge) N-4a B (Groundwater Banking) N-4b C (Recycled Water)N-4c D (Conservation) N-4d A,B,C,D N-5 No Additional ActionN-1 A,C,D N-3 A,B,C,D N-6 No Additional ActionD-0 C,D D-2

Simulation Cases and Components

Hydrologic Scenarios Normal Year Multiple Dry Year

What are the Demand Assumptions? From year 2001 – 2030: Agricultural groundwater demand increase based on land use increases by 2,250 acres Private domestic groundwater demand increases according to projected population growth Urban groundwater demand increases unless additional imported urban supply is obtained Additional model assumptions: No seasonal variations Recharge reaches the water table immediately

Stormwater Recharge Basin Cells Wet season flood waters diverted into recharge ponds and/or wetlands along Sonoma Creek Recharge ponds placed in areas of highest drawdown along Sonoma Creek cover 80 acres loading of 0.1 ft/d for 120 days/year 960 AF per year Implementation in 2015 Total volume 15,360 AF over 16 years ( ) Option A Storm Water Recharge

Groundwater Banking Groundwater banking of imported winter surplus water Two groundwater recharge wells placed in area where model shows highest drawdown Recharging middle aquifer zone Rate 1cfs (465 gpm) per well Average 1,500 AF per year total for both wells Implementation in 2015 Total volume 24,000 AF over 16 years ( ); 1 cfs per well Option B Groundwater Banking

Recycled Water Alignment 1 in Sonoma Valley Recycled Water Draft Feasibility Study (Agency, 2005) In lieu agricultural irrigation 1,100 AF per year starting in 2010 Phased implementation Total volume 23,100 AF over 21 years ( ) Option C Recycled Water

Conservation Urban groundwater demand: – Tier One To- Date and plumbing code conservation measures – All measures (Tier One Future, 50 % of Tier Two, New Development, Plumbing Code) Projections provided by Agency Domestic groundwater demand: – linear ramp up – 8.3% conservation Agricultural groundwater demand: – linear ramp up – 5% conservation Option D Increased Conservation

What Did We Learn?

Simulated Drawdown Case D-0 30-yr dry weather scenario No additional imported water No additional action Change in Storage -22,000 AF

Simulated Drawdown Case N-0 30-yr normal weather scenario No additional imported water No additional action Change in Storage -18,900 AF

Simulated Drawdown Case N-1 30-yr normal weather scenario Additional imported water No additional action Change in Storage -16,000 AF

Simulated Drawdown Case D-2 30-yr dry weather scenario Additional imported water Recycled water & conservation options Change in Storage -10,900 AF

Simulated Drawdown Case N-3 30-yr normal weather scenario Additional imported water Stormwater recharge, recycled water & conservation options Change in Storage -5,700 AF

Simulated Drawdown Case N-4b 30-yr normal weather scenario No additional imported water Groundwater banking Change in Storage -1,600 AF

Simulated Drawdown Case N-5 30-yr normal weather scenario No additional imported water Stormwater recharge, groundwater banking, recycled water, and conservation Change in Storage +8,400 AF

Simulated Drawdown Case D-6 30-yr dry weather scenario Additional imported water Stormwater recharge, groundwater banking, recycled water, and conservation Change in Storage +8,400 AF

Simulated Drawdown Case N-6 30-yr normal weather scenario Additional imported water Stormwater recharge, groundwater banking, recycled water, and conservation Change in Storage +11,100 AF

What Did We Learn? Based on projected demand, the basin groundwater levels and storage will continue to decline Active water management is necessary in the future to minimize and potentially mitigate declines Groundwater banking (Option B) is the most effective water management option considered It is the only option which provides a positive basin groundwater storage result All water management options should be utilized to improve water supply reliability for future generations

What’s the Model Been Telling Us? Declining groundwater storage and levels Water management is necessary Groundwater Banking Provides the greatest increase in storage The only option that provides sustainable groundwater conditions in basin

Why is the Model Helpful? It allows us to look at the amount of water entering and exiting the basin A groundwater model is the best tool available for predicting future groundwater conditions Despite its limitations, it is a useful tool for comparing various proposed water management options

How Can We Use the Results? The results…. Can help prioritize water management options Confirm the need for active water management Help identify the areas of largest deficit Help identify additional data and enhancements needed for the model

For What Can the Results NOT Be Used? Detailed siting and design of water management options Local-scale evaluation of groundwater conditions Limitations Uncertainty in key input data Deep lateral in/outflows not considered Limited data on Sonoma Creek Large regional-scale model Freshwater conditions Fully saturated conditions

Sensitivity Analysis

Model most sensitive to Recharge Sonoma Creek streambed conductance Horizontal hydraulic conductivity in north basin Sensitivity Analysis

How Will the Model be Improved? Improved characterization of…. Amount and distribution of recharge Sonoma Creek gains and losses Hydrogeologic conceptualization Groundwater level and groundwater quality Groundwater production through updated land use survey and use estimation

Questions?

Recharge – Calibrated Model 1976: Single Driest Year : Driest Consecutive Years Source: USGS MODFLOW Model report, Table 6