Groundwater / Surface Water Interaction: Measure, Model, Mitigate? The VenturaRiver Example
by Jordan Kear - Kear Groundwater
Santa Barbara, Ca.
Abstract: A close link between surface and groundwater in the VenturaRiverGroundwaterBasin has long been recognized, yet the understanding and quantification of the resources has only just begun in recent years. An independently-sustained watershed in southern California - meaning that nowater is imported from outside the watershed for delivery to cities, residences, or agriculture - the VenturaRiver watershed has four alluvial groundwater basins, numerous bedrock formations which yield water to wells, major surface water reservoirs and an ephemeral river.
Several rounds of studies have stressed the need and importance for quantification of surface water and groundwater interaction, driven by both human demands and environmental water demands. Detailed monitoring of water levels and flows in the seasonally charged Ventura River, pumping testing of wells near the river, and detailed observations of locations and rates of surface flow are part of an ongoing monitoring program. Acute effects of pumping of proximal wells on river flow have been both measured and modeled to be very small, but the data are useful for modeling the cumulative effects of pumping over the dynamically wet and dry reaches of the river.
Findings indicate that compared to extractions and diversions from the system, natural discharge, evapo-transpiration, and aquifer morphology are major factors in groundwater levels, surface water presence, absence, and timing of changes. Natural and human infered factors contributing to surface and groundwater demands are beginning to be understood, which warrents concern with the prospect of a (Total Maximum Dalily Limits) TMDL on "pumping and diversions" from the river looming. The alternative of a Memorandum of Understanding / Memorandum of Agreement among key stakeholders including purveyors, private pumpers, regulators, and the environmental community also bears merit and discussion The methods and outcomes of the studies, the scope and limitations of modeling efforts, and cooperative mitigation strategies have been valuable in understanding the nuances unique to the Ventura River, but are certainly applicable in other watersheds as the focus on competing demands steer the issues of sustainability.
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