Numerical modeling was used to generate pore-scale structures with different structural properties. They were partially saturated according to wetting and drainage regimes using morphological operations for a range of saturations. The hydraulic and electrical conductivities of the resulting partially saturated grain packs were numerically computed to produce relative hydraulic conductivity versus saturation and relative electrical conductivity versus saturation curves. The relative hydraulic conductivities were then compared to the relative electrical conductivities for the same saturations and it was found that relative hydraulic conductivity could be expressed as relative electrical conductivity to a power law exponent, b. This exponent b was not correlated to porosity, specific surface area, or tortuosity. It did change according to whether the soil was wetting or draining. However, a b value of 2.1 reproduced relative hydraulic conductivity from relative electrical conductivity with little added error. The effects of surface conduction on the observed power law relationship due to either low fluid electrical conductivity or increased clay content were analyzed. The relationship was found to hold for fluid conductivities typical of groundwater and for clay content of less than 5% if the clays were layered perpendicular to electrical flow. The relationship breaks down for electrical flow parallel to clay layers, which makes the choice of electrode arrangement important in cases where clay may be present. This relationship can be used with secondary pressure or saturation data to characterize a soil's hydraulic conductivity curve.

Infiltration rate is the key parameter that describes how water moves from the surface into a groundwater aquifer during managed aquifer recharge (MAR). Characterization of infiltration rate heterogeneity in space and time is valuable information for MAR system operation. In this study, we utilized fiber optic distributed temperature sensing (FO-DTS) observations and the phase shift of the diurnal temperature signal between two vertically co-located fiber optic cables to characterize infiltration rate spatially and temporally in a MAR basin. The FO-DTS measurements revealed spatial heterogeneity of infiltration rate: approximately 78% of the recharge water infiltrated through 50% of the pond bottom on average. We also introduced a metric for quantifying how the infiltration rate in a recharge pond changes over time, which enables FO-DTS to be used as a method for monitoring MAR and informing maintenance decisions. By monitoring this metric, we found high-spatial variability in how rapidly infiltration rate changed during the test period. We attributed this variability to biological pore clogging and found a relationship between high initial infiltration rate and the most rapid pore clogging. We found a strong relationship (R = 0.8) between observed maximum infiltration rates and electrical resistivity measurements from electrical resistivity tomography data taken in the same basin when dry. This result shows that the combined acquisition of DTS and ERT data can improve the design and operation of a MAR pond significantly by providing the critical information needed about spatial variability in parameters controlling infiltration rates.

Effi ciency of managed aquifer recharge (MAR) via surface infi ltra on ponds relies heavily on the proper es and processes of the unsaturated zone. The spa al and temporal resolu ons needed in data for monitoring such processes are higher than typical hydrologic data can provide. Recently developed direct-push resis vity probes can be located in the base of a MAR pond and used to obtain ver cal electrical conduc vity profi les with high spa al and temporal resolu ons. In this study, we developed an inversion algorithm that uses a ver cal electrical conduc vity profi le and auxiliary hydrologic data to es mate the van Genuchten parameters and saturated hydraulic conduc vity of a homogeneous unsaturated zone. Using a synthe c case, we analyzed the method's accuracy and sensi vity to temporal and spa al resolu ons in data. We then derived a new rela onship for using the parameter es ma on and electrical conduc vity data to es mate infi ltra on rates and pond bo om clogging in situ in real me, extending electrical resis vity as a method for gaining qualita ve infi ltra on informa on to a tool for quan ta ve infi ltra on rate monitoring. We found that we were able to best es mate the logarithm of the saturated hydraulic conduc vity, which was within 5% of the true value for all cases. The van Genuchten parameter α was the least accurately predicted parameter, devia ng at most 22% from the true value. We found that we could es mate infi ltra on rates and pond bo om clogging with a level of accuracy appropriate for use in modeling and management decisions, in most cases to within 11% of the true value.Abbrevia ons: MAR, managed aquifer recharge.Managed aquifer recharge is the inten onal act of storing water in aquifers. h e purposes of MAR include storing water for later use and reversing or preventing seawater intrusion or aquifer overdrat (Bouwer, 2002). More recently, using the subsurface as a water bank with the intention of direct recovery of the recharged water, rather than just the goal of aquifer replenishment and overdrat protection from local pumping, has become an ot en-used water management tool. h is need for MAR will continue to increase in the future because it is an instrument in balancing water supply and demand that has many benei ts over traditional surface storage systems. Managed aquifer recharge needs much less space than dams and reservoirs, is more economically feasible at a smaller scale, and has lower evaporative losses. It is also an ef ective receptacle for recycled or reclaimed water. h is use allows water to be kept in the watershed, making an area less dependent on distant water sources (Dillon, 2005).Designing an ei cient, successful MAR project with direct recovery is not simple, however. Managed aquifer recharge can be performed via injection through wells or, as is becoming more common, via ini ltration through ponds, banks, dunes, and other surface storage units (Dillon, 2005). h e addition of water to an aquifer via an ini ltration pond causes mounding of the water table on top of th...