Using Sediment Texture to Estimate Infiltration Rates at a Managed
Aquifer Recharge Site
Abstract
UCSC GEOPATHS is an NSF-supported initiative to improve undergraduate
success in the geosciences, driven by a desire to broaden academic
engagement. One component of the program is a funded undergraduate
summer program that provides authentic, professional experiences –
across all employment sectors – to increase commitment in the
geoscience pipeline. Many hydrologic basins rely on groundwater to
supply domestic, municipal, and agricultural demand, but resources are
increasingly stressed by rising demand, changes in land use, and a
shifting climate. Consequences of groundwater overdraft include drying
surface water systems, land subsidence, and seawater intrusion. Managed
aquifer recharge (MAR) can help improve groundwater resources by
increasing infiltration of excess surface water. We are part of a
research team assessing hydrologic conditions during MAR on an active
vineyard in Central California, through diversion of high flows from an
adjacent river, a strategy known as “flood-MAR.” Our team collected
soil samples from the upper 100 cm below ground surface at 24 locations
across the 785-acre field site. We analyzed samples for soil texture at
10-cm spacing using a particle size analyzer based on laser light
scattering. Preliminary analysis of fractions of sand, silt, and
clay-sized particles indicate some lateral continuity from site to site.
The northern part of the field area appears to be finer grained, on
average, consistent with regional soil maps, but there is also
considerable variability with depth. These data will be used to assess
variations in expected infiltration rates by combining soil texture (to
estimate infiltration capacity) and potential flood and saturation
depths (to bracket vertical head gradients). Studies of this kind are
helpful for assessing the efficacy of flood-MAR as a strategy to improve
groundwater supplies and quality.