California’s Sustainable Groundwater Management Act of 2014 (SGMA) requires that Groundwater Sustainability Agencies (GSAs) manage groundwater resources to avoid significant and unreasonable adverse impacts on beneficial uses of interconnected surface water1, 2. Surface Water Depletion is one of the six SGMA Sustainability Factors that GSAs and their Groundwater Sustainability Plans (GSPs) must consider and endeavor to avoid or minimize3.
Beneficial uses of surface water include both human consumptive uses and environmental uses – therefore the SGMA obligates GSAs to manage the groundwater resource to also protect groundwater-dependent ecosystems3. Interconnected surface water is defined as “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.” 4
As a result of the SGMA mandate to protect beneficial uses of surface water, GSAs will need to develop a deep understanding of the dynamic interactions between groundwater and surface water in their basin – flow can occur in either direction, driven by hydraulic gradients that fluctuate on a range of time scales. In the following figure, A is a gaining stream reach that receives water from the groundwater system, whereas, B is a losing reach that contributes water to the groundwater system5. A stream can have both gaining and losing reaches along its length, depending on many local factors.
While there are a number of tools and methods for quantifying flow between groundwater and surface water (see Table 2 (p 9-10) of Cantor and others, 20182), the flow-net analysis method, often called the “Darcy approach,” is probably the most frequently used6. In this method, a combination of measurements of levels in near-shore water-table wells and measurements of water stage of adjacent surface-water bodies are used to calculate water-table gradients between the wells and the surface-water body. Quantifying hydraulic gradients in space and time and applying the Darcy equation, enables the GSAs to better understand the magnitude and dynamics of flow between surface water and groundwater.
It is critical for GSPs to recognize the spatial and temporal scale of the groundwater/ surface-water interaction to be managed, so that networks can be designed to provide appropriately scaled data. The following table shows that the appropriate temporal scale of data collection for “Monitoring ground-water and surface-water interaction” can range from days/weeks to decades7. For the seasonal- and hydrological event-driven conditions many GSA basins will be experiencing, monitoring frequency at the shortest temporal scale will likely be most valuable.
Creating groundwater and surface-water monitoring networks to achieve the appropriate spatial and temporal density is key to achieving the deep understanding needed by the GSAs. To this end, leveraging existing groundwater monitoring networks will be important, as will be, taking advantage of new technology. The Wellntel Groundwater System (sensor and analytics platform) complements and extends existing networks by adding private pumping wells as water-level monitoring points, and by integrating data from all network sources and third-party data into a powerful Analytics Dashboard to streamline data management, analysis, visualization, and reporting. The Wellntel Groundwater System is the most effective approach to provide the spatial and temporal density that will be required to meet the SGMA mandate to protect beneficial uses of surface water.
Contact Wellntel to learn about networks operating in California and across the US. We can help you achieve your monitoring objectives in better, faster, and more economical ways.
1 Cal. Water Code § 10721(x)
2 Cantor, Alida, Dave Owen, Thomas Harter, Nell Green Nylen, and Michael Kiparsky, 2018, Navigating Groundwater-Surface Water Interactions under the Sustainable Groundwater Management Act, Center for Law, Energy & the Environment, UC Berkeley School of Law, Berkeley, CA. 50 pp, accessed at https://www.law.berkeley.edu/wp-content/uploads/2018/03/Navigating_GW-SW_Interactions_under_SGMA.pdf
3 California Department of Water Resources, 2017, DRAFT Best Management Practices for the Sustainable Management of Groundwater, Sustainable Management Criteria, accessed at https://water.ca.gov/LegacyFiles/groundwater/sgm/pdfs/BMP_Sustainable_Management_Criteria_2017-11-06.pdf
4 Cal. Code Regs. tit. 23, § 351(o)
5 Barlow, P.M., and Leake, S.A., 2012, Streamflow depletion by wells—Understanding and managing the effects of groundwater pumping on streamflow: U.S. Geological Survey Circular 1376, 84 p., accessed at https://pubs.usgs.gov/circ/1376/pdf/circ1376_barlow_report_508.pdf
6 Donald O. Rosenberry, James W. LaBaugh, and Randall J. Hunt, 2008, Use of Monitoring Wells, Portable Piezometers, and Seepage Meters to Quantify Flow Between Surface Water and Ground Water, Chapter 2, in Rosenberry, D.O., and LaBaugh, J.W., 2008, Field techniques for estimating water fluxes between surface water and ground water: U.S. Geological Survey Techniques and Methods 4–D2, 128 p., accessed at https://pubs.usgs.gov/tm/04d02/pdf/TM4-D2-chap2.pdf
7 Taylor, C. J., and Alley, W. M., 2001, Ground-water-level monitoring and the importance of long term water-level data: U.S. Geological Survey Circular 1217, accessed at https://pubs.usgs.gov/circ/circ1217/pdf/circ1217_final.pdf