Gil Strassberg

Evaluation of groundwater storage monitoring with the GRACE satellite: Case study of the High Plains aquifer, central United States

(450,000 km 2 area), which is subjected to intense irrigation. GRACE-derived terrestrial water storage (TWS) is highly correlated with the sum of soil moisture (SM) and groundwater storage (GWS) (R = 0.96 for in situ measured SM from 78 stations and R = 0.95 for simulated SM with the Noah land surface model with root-mean-square difference of 38 mm and 36 mm, respectively). Correlation between seasonal GWS changes calculated from GRACE TWS minus SM and measured GWS (� 1000 wells per season)isalsohigh(R=0.73forinsituSMandR=0.72forsimulatedSM).VariabilityinSM is mostly restricted to the upper 2 m of the soil. Monitored SM compared favorably with simulated SM (R = 0.82). Study results show the potential for using GRACE gravity measurements to monitor TWS and GWS over large semiarid regions subjected to intense irrigation.

Impact of deep plowing on groundwater recharge in a semiarid region: Case study, High Plains, Texas

(20,000 km 2 area) in a bench terrace system in the semiarid High Plains in Texas (USA). Deep plowing was followed by conventional tillage. Boreholes were drilled in deep plowed cropland (three boreholes) and also beneath conventionally tilled cropland (four) and natural ecosystems (three) to provide baseline controls. Soil samples were analyzed for water content, chloride concentrations, and matric potentials to quantify subsurface water movement. Bulges of chloride that accumulated beneath natural ecosystems during the past 9,000–14,000 years (Holocene period) provided a marker to quantify timeintegrated response of subsurface drainage to hydrologic forcing in deep-plowed cropland. Displacement of chloride bulges to depths of 10.7, 12.3, and 13.7 m beneath deep-plowed cropland indicate minimum drainage rates of 58, 60, and 81 mm/a, whereas drainage beneath conventionally tilled cropland ranged from 0 (nonterraced) to 9 and 14 mm/a (bench terraced). Deep plowing slightly increased crop yield during wet years by reducing waterlogging. If deep plowing were applied to 10% of the Pullman soils, it could increase regional volumetric recharge by 0.1 km 3 /a, which is similar to the current regional

Automated well permitting via GIS geoprocessing tools.

In this paper we describe a GIS-based system for automated well permitting. The system involves the integration of a calibrated MODFLOW groundwater model into an ArcGIS geodatabase using the Simulation feature dataset in the Arc Hydro Groundwater data model. The model is then used as a baseline for the analysis of candidate wells. Each candidate well is added to the model and the model is run to determine the impact of the well on streamflow, drawdown, etc. The entire process is implemented using a series of connected, low-level geoprocessing tools resulting in a simple automated process. The automation serves to reduce error and increase efficiency. The outputs include tables and GIS maps. The process, evaluation criteria, and products can be customized on an agency-by-agency basis. We illustrate the process using case studies from Virginia and Florida.