Assessing the Stream-Aquifer Interaction for SGMA Compliance: A possible approach (to be refined) GRA/DWR – Workshop: STREAM DEPLETION THROUGH THE SGMA LENS August 29, 2017 Maurice Hall Associate Vice President, Water Environmental Defense Fund

Environmental Defense Fund Water Program Vision Balanced and resilient water systems that meet the needs of people and nature In the context of SGMA: Proactively manage for multiple benefits Nature Disadvantaged communities Farms & cities Priorities Provide for ecosystems Provide for disadvantaged communities Trading programs (transition to balance and provide resilience) Surface water depletion (resilience of whole water system) Storage (resilience for people and nature)

Surface Water/Groundwater Interaction Legislation: Undesirable Result #6: “Depletions of interconnected surface water that have significant and unreasonable adverse impacts on beneficial uses of the surface water.” Regulations (DWR): Define “interconnected surface water” Require: ID of interconnected surface waters Estimation of groundwater conditions Water budget, including inflows and outflows to surface water Minimum thresholds – in volumes – for depletion of surface water Description of the model or method used to estimate depletions As defined in the regulations, Interconnected surface water” refers to surface water that is hydraulically connected at any point by a continuous saturated zone to the underlying aquifer and the overlying surface water is not completely depleted. (f) Identification of interconnected surface water systems within the basin and an estimate of the quantity and timing of depletions of those systems, utilizing data available from the Department, as specified in Section 353.2, or the best available information. Water Budget (b) The water budget shall quantify the following, either through direct measurements or estimates based on data: Total surface water entering and leaving a basin by water source type. (2) Inflow to the groundwater system by water source type, including subsurface groundwater inflow and infiltration of precipitation, applied water, and surface water systems, such as lakes, streams, rivers, canals, springs and conveyance systems. (3) Outflows from the groundwater system by water use sector, including evapotranspiration, groundwater extraction, groundwater discharge to surface water sources, and subsurface groundwater outflow. Minimum Thresholds for each sustainability indicator shall be defined as follows: (c)(6) Depletions of Interconnected Surface Water. The minimum threshold for depletions of interconnected surface water shall be the rate or volume of surface water depletions caused by groundwater use that has adverse impacts on beneficial uses of the surface water and may lead to undesirable results. The minimum threshold established for depletions of interconnected surface water shall be supported by the following:  The location, quantity, and timing of depletions of interconnected surface water. A description of the groundwater and surface water model used to quantify surface water depletion. If a numerical groundwater and surface water model is not used to quantify surface water depletion, the Plan shall identify and describe an equally effective method, tool, or analytical model to accomplish the requirements of this Paragraph.

Some Ambiguities or Complications “Depletions of interconnected surface water that have significant and unreasonable adverse impacts on beneficial uses of the surface water.” When you look at a stream in California – For many – if not most – streams, all of the water is fully allocated a large part of the time. Water supplies – someone has a right to divert it downstream In-stream flows – required flows for fish and wildlife Water quality -- flows to maintain water quality It would be convenient to if we could manage the groundwater to deplete only when there was “unallocated” water in the stream. But – it’s difficult to turn groundwater depletion on and off Difficult (impossible?) in most circumstances – to say, 1) let’s turn on our depletion when there is unallocated flows in the stream, and 2) let’s adjust our depletion so that it is less than or equal to the amount of unallocated flow in the stream when there is unalloca

Some Ambiguities or Complications “Depletions of interconnected surface water that have significant and unreasonable adverse impacts on beneficial uses of the surface water.” Now let’s look at “Significant and unreasonable.” What is significant and unreasonable? We struggle with this a lot in California water management. Now, given that our estimates of stream flow depletion – whether from monitoring or modeling – have some pretty large error bars, It’s going to be challenging to say whether it’s significant and unreasonable. My estimate says it’s only 1000 af/yr – is that significant and unreasonable ? Well, is your estimate off by a factor of two? Maybe it’s 2000 af/yr – is that significant and unreasonable? When does your 1000 af/yr occur In the summer when temperatures are critical In the winter, when there’s a good chance there’s excess flow That probably affects what is significant and unreasonable.

Simplification for Ambiguities “Depletions of interconnected surface water that have significant and unreasonable adverse impacts on beneficial uses of the surface water.” Let’s assume – as a default: Increased depletions are significant Adversely impact beneficial uses GSA can decide the default condition doesn’t exist, but must demonstrate why

Pre-2015 Conditions “The plan may, but is not required to, address undesirable results that occurred before, and have not been corrected by, January 1, 2015.” Baseline condition for sustainability – prior to 2015 Use best available information Allow for inter-annual and intra-annual variability Some impacts from pre-2015 pumping yet to show up at streams

Pumped Groundwater Basin Past or Current Level of Use Ground Surface River In a basin with a moderate level of pumping With historic pumping, groundwater levels have been drawn down below the level of streams that flow across the basin This induces flow of water from the stream to the aquifer This stream leakage is part of the recharge to the groundwater basin If this level of pumping continues, the basin will come to equilibrium This means levels will stabilize Although levels may go up and down as wetter and dryer periods pass, overall the levels will remain stable over muliple years Similarly, leakage rates from the stream to the groundwater will remain relatively constant Groundwater Level Recharge/Leakage from River

Pumped Groundwater Basin Future, with Increased Pumping Important note: Illustration shows losing stream Issue is the same for gaining or losing stream reaches (decreased accretion = stream depletion) River Ground Surface If new wells are drilled and pumping is increased Groundwater levels will go down This increases the gradient of groundwater flow away from the stream Also leakage from the stream to the groundwater increases with lower water levels This means less flow is left in the stream – and surface water supplies are further impacted If these pumping rates continue, the groundwater levels may again stabilize, but at lower levels These levels will stabilize, however, only if enough additional flow can be drawn in from the river to compensate for the increased pumping rates Increased Leakage from River Groundwater Level

For Stream Depletion Gradient Near River is Key Key – Groundwater Levels along River Corridor River Ground Surface Groundwater Level

Basic Approach for Compliance with Stream Depletion Maintain Groundwater Gradient Near the Stream Assume stream levels are the same in the future as in the past Set minimum threshold for groundwater levels in the vicinity of streams Conduct modeling to assess trajectory of levels Develop management plan to maintain levels near stream at or above thresholds Monitor and adjust actions to maintain threshold levels River

Basic Approach for Compliance with Stream Depletion Advantages of this Approach Allows management flexibility Groundwater levels distant from stream can vary more widely Wide range of actions available for maintaining levels Analogous to salt water intrusion approaches and strategies Avoids problem of inaccuracies in depletion estimation River

Basic Approach for Compliance with Stream Depletion Setting Minimum Thresholds Use best available information Well levels Modeling Allow for seasonal and annual variation (reflecting historical) Establish monitoring network to Verify assumptions Improve understanding & models Adjust thresholds as understanding improves River

Basic Approach for Compliance with Stream Depletion Challenges & Outstanding Questions How far? – How Close? Best way to deal with lack of historical information (Best available model?) Wells near streams 1/8 mile? 2 miles? River

Basic Approach for Compliance with Stream Depletion My Rationale for This Approach Achieves the intent of the law Avoids difficult issue of actually quantifying stream depletion Tend to manage to groundwater LEVELS Maintains management flexibility at distance from stream Simplifies communication/discussion – consistent with “zone” concept Management flexibility River