1. Proposed Solution: Mass balance, spatial interpolation, and transient analysis Proposed Solution: Mass balance, spatial interpolation, and transient analysis Problem Description: Quantitative characterization of gaining and losing segments of rivers Problem Description: Quantitative characterization of gaining and losing segments of rivers Assessing Ground Water – Surface Water Exchanges in a Complex River Regime Henry Pai, Jason C. Fisher, Sandra R. Villamizar, Christopher Butler, Alexander A. Rat’ko, Thomas C. Harmon School of Engineering, UC Merced Introduction: Studies at San Joaquin River-Merced River confluence Introduction: Studies at San Joaquin River-Merced River confluence Multiscale Data Approach Regional scale –Gauging stations at one transect site for method verification and others several km’s upstream for regional water balance Local scale –Hydrolab multi-parameter sonde for point water quality data –Sontek acoustic Doppler velocimeter (ADV) for point water velocity data –NIMS RD delivers Hydrolab and Sontek for high granularity transect data –Three transect locations near confluence for local water balance –Valeport Midas Surveyer and Leica surveying equipment for river bathymetry –Leica surveying equipment for floodplain topography Methods Center for Embedded Networked Sensing UCLA – UCR – Caltech – USC – UC Merced At large scales, net groundwater-surface water exchange are often estimated from flow gauges. However, quantifying smaller scale river reaches is becoming important in assessing non-point source pollution and ecological restoration efforts. An example of importance includes estimating agricultural influences transported from groundwater to surface water and the effects of the nutrient rich water organisms and overall river ecology. The confluence of the SJR and Merced River provides an unique mixing region of a heavily polluted river, (SJR), with a clean river, (Merced), where likely groundwater- surface water interaction occurs. Using NIMS RD as a delivery an ADV and multi-parameter sonde simultaneously, flow and constituent fluxes can be calculated and mass balances with multiple transects. This work extends this approach to the confluence by deploying three transects, two for the rivers upstream and one downstream of the confluence, with hopes to quantify groundwater-surface water exchange at this sub-km scale. Results Experimental goals –Refine methodology for measuring river flow and constituent mass balances at sub-km scale –Deploy of tethered robotic system NIMS RD at multiple transects with assorted sensors Scientific goals –Calculate flow and solute mass balances between three observational transects at the confluence zone of two rivers –Perform sensitivity analysis due to unsteady conditions –Delineate ground water – surface water fluxes for water quality and related ecological processes Overview [Above] Merced River flowing from left and San Joaquin River (SJR) from right. NIMS RD shown delivering sensor package after confluence. Boundary values –Site digital elevation map, DEM, is spatially interpolated using multilevel B- splines from sonar and survey data –Bathymetry coupled with shore GPS locations for a transect define the river bed topology for a transect Unsteady conditions –Ideally under relatively steady flow, mass balance can be calculated with certain confidence over a short period required for re-deploying NIMS RD with sensor package for the three transects –Changes of flow along Merced River during overall deployment complicated calculation –Assuming no diffusion, genetic algorithm used to estimate travel time for Merced River using larger-scale flow gauge data Flow and water quality values –Flow velocity and water quality parameters are also spatially interpolated using multilevel B-splines to and integrated with area for volumetric flow of water and mass transport [Right] Interpolated DEM of river and surrounding surface with labeled significant locations [Above] Left 3 plots show interpolated contour of flow velocity. Right 3 plots show interpolated contour for the specific conductivity, a water quality parameter measured by the Hydrolab multi-paramter sonde. Challenges [Above] Regional site with gauging stations denoted by dots and corresponding river network diagram. [Below] Flow histories for the study period from gauging station data. [Left] Assorted transect values for volumetric flow and total dissolved solids, with flow histories of NEW gauging station and adjusted MST* flow history for travel time. Highlighted region shows when mass balance calculation is taken. –For the transect near the NEW gauging station, the calculated volumetric flows were on average 4.3% below the flow reported by the gauging station –After adjustment for a travel time 6.25 hrs, the estimated groundwater input, gain, from the confluence site was 0.15 m 3 /s –Accounting for travel time sensitivity, the range for groundwater- surface water exchange was 0.2 m 3 /s loss to 0.5 m 3 /s gain Future Work –Tracer experiments to help assess transient nature of flow –Use of NIMS AQ and an acoustic Doppler current profiler for faster transect flow data collection –Use of adaptive sampling techniques for faster water quality parameter data collection –Include data collected for coupled groundwater-surface water models and other parametric models such as energy, reaeration, and biogeochemical models