Hydrogeologic Conceptual Models for Regional Flow Systems

Transcription

1 Hydrogeologic Conceptual Models for Regional Flow Systems R.T. Hanson, U.S. Geological Survey One Water Hydrologic Flow Model USGS MODFLOW-OWHM Session 4 Groundwater Subbasin Baseline Historic and Current Conditions Assessment, and Determining Base Period for Sustainable Yield GRA SGMA Workshop Sacramento, California, June 8, 2016

2 Types of Flow Systems & Hydogeolgic Conceptual Models Convergent or Divergent Flow systems, Lateral or Vertical Flow dominated, Faulted - Compartmentalized, Multiple Provenance Linked basins/subregional areas Hydrogeologic settings are a mixture of Geologic History (Framework) and Human development of the resources.

3 Types of Flow Systems & Hydogeolgic Conceptual Models These features affect the secondary effects of overdrafted basins: Groundwater-level declines. Groundwater-storage reductions. Seawater intrusion. Water-quality degradation. Land subsidence. Interconnected surface-water depletions. They also affect their ability to achieve sustainability +/- mitigation, and potentially affect neighboring regions with separate GSPs

4 Three Conceptual Examples Santa Clara Example Pajaro Valley Example Cuyama Valley Example

5 Santa Clara Valley is a Convergent Flow System, linked to an upstream basin and are subject to all the secondary effects of SGMA seawater intrusion, land subsidence, storage depletion, streamflow capture Hanson, 2015

6 Santa Clara Valley is a Layered and Compartmentalized Flow System with geologically controlled lateral flow The basin is faulted into three subregions but the the Alluvial layers overlap these subregions Hanson et al, 2003

7 Santa Clara Valley is a Layered and Compartmentalized Flow System lateral flow dominated and a classic example of a basin that has been transformed with vertical flow as multi-aquifer Wellbore flow 8 Recent Glacial cycles represent layers Hanson, 2015

8 Santa Clara Valley has vertical flow as multi-aquifer Wellbore flow that has become a major component of conjunctive use that affects confined aquifer recharge, streamflow infiltration, storage depletion, and land subsidence Hanson, 2015

9 Three Conceptual Examples Santa Clara Example Pajaro Valley Example Cuyama Valley Example

10 Pajaro Valley is a Layered Multi- Aquifer, Convergent Flow System, linked to an upstream basin and downstream regions and have some secondary effects of SGMA seawater intrusion & storage depletion Regional Cones of depression in gw levels Hanson et al, 2014

11 Pajaro Valley Hydrologic Model Water-balance subregions used in PVHM to assess conjunctive use, coastal pumpage, and related sea water intrusion in Pajaro Valley, California (modified from Hanson et al. 2014).

12 Basin Geology: Map View Four geologic units exposed at the surface: Alluvium Upper Aromas Purisima Basement Units are heterogeneous (vary spatially) Pajaro Valley Water Management Agency Hanson et Hanson al, 2014 et al. (in prep.)

13 Basin Geology: Profile View 6 Model Layers: Alluvium Alluvial Confining Unit Upper Aromas Aromas Confining Unit Lower Aromas Purisima Hanson et et al. al, (in 2014 prep.) Pajaro Valley Water Management Agency

14 Alluvial Fine-grained Confining Unit >33% fines (P) & <33% fines (O) Hydraulic Property Parameter Zones Fluvial Facies of Aromas Fm East & West of Zayante Fault (Fluvial/Marine) Purisima Fm. Eolian Facies of Aromas Fm Hanson et al, 2014

15 Coastal delivery & import pipeline components of BMP projects ASR WWTP D City of Watsonville Capture extra runoff for ASR inflow at head gate of Harkins Slough at confluence with Watsonville Slough Coastal Delivery System (CDS) Streamflow Infiltration and Supplemental Pumpback Wells Proposed Import Pipeline Developed Scheme to Capture Runoff & Deliver to Ag (integrating Harkins Slough Diversion/ASR and CDS within PVHM Model) Split CDS into pieces that are aligned with New Water- Balance Subregions +/- CDS Other Districts

16 Example of Future Analysis of Current Mitigation Projects Using MF-OWHM Used to develop a new Basin Management Plan that includes additional projects to reduce overdraft & increase capture/use of local runoff, recycled water, ASR, & MAR (Hanson et al., 2014)

17 Example of analysis of coastal groundwater flows historical conditions and future mitigation with current projects using MF-OWHM Reduced inflows by about half but about half of the recovery is additional seawater inflows with reduced coastal pumpage (Hanson et al., 2014).

18 Three Conceptual Examples Santa Clara Example Pajaro Valley Example Cuyama Valley Example

19 Cuyama Valley is sole-source layered Multi-Aquifer, Compartmentalized, Convergent Flow System, and subject some secondary effects of SGMA poor water quality, land subsidence, storage depletion, streamflow capture

20 Summary of Findings Three different major zones of the Basin: Main Zone Ventucopa Uplands Sierra Madre Foothills Imbalance of 29,900 Acre-Feet per year for overall Basin (SBCWA ,000 Acre- Feet per year) Very poor water quality; Calcium-Magnesium Sulfate dominated with total dissolved solids on the order of ppm on average Water age up to 33,000 years (Everett et al., 2013; Sweetkind et al., 2013; Hanson et al., 2014)

21 Main Zone Representative Hydrograph depicting water level declines of up to 400 since around 1950 ~400 ft

22 Modeled Changes in Historical Groundwater Storage in the Cuyama Valley (Hanson et al., 2014)

23 Uncorrected Age Dates of Groundwater in Cuyama Valley Aquifers in Thousands of Years before Present Almost all Samples have little to no Tritium except in Ventucopa Area Little to No Modern Recharge (Last years)

24 Measured Subsidence Since 2000 Continuous GPS from Plate Boundary Observatory site ~.26 ft

25 Modeled Additional changes of up to 300 more declines in Projected Groundwater Levels in Cuyama Valley for Base-Case Scenario Hanson et al, 2014

26 Some Basic Conclusions about Conceptual Models Hydrologic Budgets will be complex and multi-part Multiple sustainability criteria will be needed Sustainability with some mitigation may be needed for selected subregions based on criteria The Hydrogeologic Conceptual Model needs to be consistent with the features affecting flow & may require management of different subregions differently

27 { QUESTIONS