Distributed hydrologic models capable of simulating fully-coupled surface water and groundwater flow are increasingly used to examine problems in the hydrologic sciences. Several techniques are currently available to couple the surface and subsurface; the two most frequently employed approaches are first-order exchange coefficients (a.k.a., the surface conductance method) and enforced continuity of pressure and flux at the surface-subsurface boundary condition. The effort reported here examines the parameter sensitivity of simulated hydrologic response for the first-order exchange coefficients at a well-characterized field site using the fully coupled Integrated Hydrology Model (InHM ). This investigation demonstrates that the first-order exchange coefficients can be selected such that the simulated hydrologic response is insensitive to the parameter choice, while simulation time is considerably reduced. Alternatively, the ability to choose a firstorder exchange coefficient that intentionally decouples the surface and subsurface facilitates concept-development simulations to examine real-world situations where the surface-subsurface exchange is impaired. While the parameters comprising the first-order exchange coefficient cannot be directly estimated or measured, the insensitivity of the simulated flow system to these parameters (when chosen appropriately) combined with the ability to mimic actual physical processes suggests that the first-order exchange coefficient approach can be consistent with a physics-based framework.Enforcing simultaneous continuity of pressure between the surface and subsurface, typically accomplished implicitly using iterative boundary condition matching, is an alternative to the first-order exchange coefficient approach, predating it by decades

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[1] Concept development simulation with distributed, physics-based models provides a quantitative approach for investigating runoff generation processes across environmental conditions. Disparities within data sets employed to design and parameterize boundary value problems used in heuristic simulation inevitably introduce various levels of bias. The objective was to evaluate the impact of boundary value problem complexity on process representation for different runoff generation mechanisms. The comprehensive physics-based hydrologic response model InHM has been employed to generate base case simulations for four well-characterized catchments. The C3 and CB catchments are located within steep, forested environments dominated by subsurface stormflow; the TW and R5 catchments are located in gently sloping rangeland environments dominated by Dunne and Horton overland flows. Observational details are well captured within all four of the base case simulations, but the characterization of soil depth, permeability, rainfall intensity, and evapotranspiration differs for each. These differences are investigated through the conversion of each base case into a reduced case scenario, all sharing the same level of complexity. Evaluation of how individual boundary value problem characteristics impact simulated runoff generation processes is facilitated by quantitative analysis of integrated and distributed responses at high spatial and temporal resolution. Generally, the base case reduction causes moderate changes in discharge and runoff patterns, with the dominant process remaining unchanged. Moderate differences between the base and reduced cases highlight the importance of detailed field observations for parameterizing and evaluating physics-based models. Overall, similarities between the base and reduced cases indicate that the simpler boundary value problems may be useful for concept development simulation to investigate fundamental controls on the spectrum of runoff generation mechanisms.Citation: Mirus, B. B., B. A. Ebel, C. S. Heppner, and K. Loague (2011), Assessing the detail needed to capture rainfall-runoff dynamics with physics-based hydrologic response simulation, Water Resour. Res., 47, W00H10,

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The physics-based model known as the Integrated Hydrology Model (InHM) is used to simulate continuous hydrologic response and event-based sediment transport for the R-5 catchment (Oklahoma, USA). For the simulations reported herein the R-5 boundary-value problem was refined, from that reported by Loague et al. (2005), to include (i) an improved conceptualization of the local hydrogeologic setting, (ii) a more accurate topographical representation of the catchment, (iii) improved boundary conditions for surface-water outflow, subsurface-water outflow and evapotranspiration, (iv) improved characterization of surface and subsurface hydraulic parameters and (v) improved initial conditions. The hydrologic-response simulations were conducted in one-year periods, for a total of six years. The sediment-transport simulations were conducted for six selected events. The multi-year water-balance results from the hydrologic-response simulations match the observed aggregate behavior of the catchment. Event hydrographs were generally simulated best for the larger events. Soil-water content was over-estimated during dry periods compared with the observed data. The sediment-transport simulations were more successful in reproducing the total sediment mass than the peak sediment discharge rate. The results from the effort reported here reinforce the contention that comprehensive and detailed datasets are crucial for testing physics-based hydrologic-response models.time-series of meteorological inputs. Continuous simulation allows transient variables to evolve into self-consistent configurations between events. The continuous simulation approach also facilitates examination of a system water balance over various temporal scales.Sediment movement through a natural landscape is the basis for nutrient cycling, channel growth and maintenance, and, ultimately, landscape evolution. The ability to understand hydrologically driven sediment-transport processes is also of key importance in making land management decisions. Because sediment transport is, in many cases, dominated by hydrologic driving forces it is important to employ a realistic flow model. Many models have been developed that consider both hydrologic response and sediment transport (Merritt et al., 2003). added a process-based sediment-transport algorithm to InHM, facilitating distributed, transient simulation of hydrologically driven erosion/deposition (also see Ran et al., 2006). Relative to many of the most widely used hydrologic-response/ sediment-transport models, the sediment-transport version of InHM employs a high degree of dimensionality and process representation (Heppner et al., 2006).The first objective of this effort was to evaluate both the ability and the utility of simulating continuous integrated hydrologic response at the catchment scale with the comprehensive physics-based InHM. The second objective of this effort was to test the sediment transport capability of InHM for selected events. The long-term monitoring data for the simulations reported here comes ...

Water-table fluctuations occur in unconfined aquifers owing to groundwater recharge following precipitation and infiltration, and groundwater discharge to streams between storm events. Groundwater recharge can be estimated from well hydrograph data using the water-table fluctuation (WTF) principle, which states that recharge is equal to the product of the water-table rise and the specific yield of the subsurface porous medium. The water-table rise, however, must be expressed relative to the water level that would have occurred in the absence of recharge. This requires a means for estimating the recession pattern of the water-table at the site. For a given site there is often a characteristic relation between the water-table elevation and the water-table decline rate following a recharge event. A computer program was written which extracts the relation between decline rate and water-table elevation from well hydrograph data and uses it to construct a master recession curve (MRC). The MRC is a characteristic water-table recession hydrograph, representing the average behavior for a declining water-table at that site. The program then calculates recharge using the WTF method by comparing the measured well hydrograph with the hydrograph predicted by the MRC and multiplying the difference at each time step by the specific yield. This approach can be used to estimate recharge in a continuous fashion from long-term well records. Presented here is a description of the code including the WTF theory and instructions for running it to estimate recharge with continuous well hydrograph data.

Abstract:In the paper that is the foundation for this study, VanderKwaak and Loague (2001 The results from two stages of model calibration are presented. The uncertainty in initial soil-water content estimates for event-based simulation is shown to be a major limitation for physics-based models. The performance of InHM, relative to past event-based simulation efforts with a quasi-physically based rainfall-runoff model, is better for both peak stormflow and the time to peak stormflow, but worse for stormflow depth. The InHM simulations reported here set the stage for continuous simulation of near-surface response for the R-5 catchment with InHM.

Obviously, not all hydrologic-response simulations can (or should) be conducted with comprehensive physics-based models. Potentially the most effective use of physics-based simulation, related to hydroecology and hydrogeomorphology, is in the design of data collection strategies and identifying the next hypothesis-testing field experiment.