Water Balance Modeling Techniques

1. Water Balance Modeling Techniques

2. Overview • Reservoir basics • Overflow_Rate, Withdrawal_Rate, changing upper bound • Using Extrema elements to track high and low extremes • Using Status elements to track the status of a Reservoir (and control actions such as pumping) • Using Time Series elements for precipitation and other histories • Using Material Delay elements to simulate seepage and flow • Using Convolution elements to simulate a runoff using a unit hydrograph • Generating stochastic precipitation, evaporation and flow histories • Using Allocators and Splitters • Using the Reliability Module to simulate equipment failure • Share your own techniques

3. Reservoir Basics • Overflow Rate • Using the Withdrawal Rate output • Varying the Upper Bound (to simulate silting up) • Using an Extrema to track peaks/valleys • Using a Status element to track status of a Reservoir and control actions (such as pumping)

4. Using Time Series Elements in Water Balance Models • Useful for inputting precipitation, evaporation and other time series • Important to: • Differentiate between rates and values • Differentiate between instantaneous flows and averages flows • Can import data from spreadsheets

5. Using Material Delay Elements to Simulate Seepage and Flow • Delay Time is mean velocity of flow • Dispersion can simulate spreading • Both can be specified as a function of hydrogeologic properties • Both may change with time (e.g., is material at field capacity?)

6. Using Convolution Elements to Simulate a Runoff Using a Unit Hydrograph • A Convolution element converts an input signal to an output signal via a transfer function • You provide an input signal (e.g., rainfall rate) and a transfer function (the unit hydrograph) • The convolution integral applies the transfer function and computes an output (e.g., runoff) • A Delay is a specialized instance of a convolution integral

7. Generating Stochastic Precipitation, Evaporation and Flow Histories • Option1: Build your own Markov (or other) model manually • Option2: Using autocorrelated Stochastics • Option3: Use the History Generator element

8. Splitters and Allocators • Should be very powerful elements for water balance models • Splitters split (distribute) flows • Allocators route flows based on specified demands and priorities

9. Using the Reliability Module to Simulate Pumps and Other Equipment • Simulate pump failure, as well as pumps turning on and off

10. Do you have any favorite techniques that you would like to share?