A continuous real-time interactive basin simulator (RIBS)

Abstract

This thesis presents enhancements to a rainfall-runoff, event-based model, the Real-Time Interactive Basin Simulator (RIBS). Major modifications are made in the description of infiltration and subsurface saturated lateral exchange processes. The infiltration model is revised to include a modified Green-Ampt scheme which allows one to account for the capillary effects during infiltration in a soil that has exponential decay of the saturated conductivity with depth. A soil moisture redistribution scheme is incorporated in the model to provide a way of simulating the dynamics of the soil moisture profile during interstorm periods. Also added is the capability of modeling the processes of lateral moisture transfer in the ground water system. An unsaturated zone - ground water coupling mechanism is implemented to account for interdependences between the two systems. All these newly added features ensure the capability of the model in applications over longer periods of time under a broader range of meteorological conditions. Another aspect of the presented work is estimation of the basin state at the beginning of a storm. A new soil moisture initialization scheme is implemented which is different from the kinematic parameterization of the soil water profile used in the previous version of the model. The initial soil moisture profile is linked to the position of the saturated zone. An independent algorithm is developed that obtains the spatial distribution of the depth to the water table in a basin based on a steady state assumption of the topography controlled ground water. This thesis presents simulations that test each of the model components. Various infiltration events are used to illustrate the sub-grid pixel behavior corresponding to ponded infiltration and infiltration under conditions of rainfall with constant and variable intensity. The ground water simulations are compared with the 2-D analytical solutions of a linearized form of the Boussinesq's equation. The overall model performance is demonstrated in applications for an artificial 1-D hillslope model and a natural watershed. These tests show the model's capability to simulate the principal phases of hydrologic response of a system that couples the unsaturated zone and ground water. Overall, the presented simulation results are physically sound and encouraging.