Abstract
Abstract. The Rainfall-Response Aquifer and Watershed Flow Model (RRAWFLOW) is a lumped-parameter model that simulates streamflow, spring flow, groundwater level, or solute transport for a measurement point in response to a system input of precipitation, recharge, or solute injection. I introduce the first version of RRAWFLOW available for download and public use and describe additional options. The open-source code is written in the R language and is available at http://sd.water.usgs.gov/projects/RRAWFLOW/RRAWFLOW.html along with an example model of streamflow. RRAWFLOW includes a time-series process to estimate recharge from precipitation and simulates the response to recharge by convolution, i.e., the unit-hydrograph approach. Gamma functions are used for estimation of parametric impulse-response functions (IRFs); a combination of two gamma functions results in a double-peaked IRF. A spline fit to a set of control points is introduced as a new method for estimation of nonparametric IRFs. Several options are included to simulate time-variant systems. For many applications, lumped models simulate the system response with equal accuracy to that of distributed models, but moreover, the ease of model construction and calibration of lumped models makes them a good choice for many applications (e.g., estimating missing periods in a hydrologic record). RRAWFLOW provides professional hydrologists and students with an accessible and versatile tool for lumped-parameter modeling.
Highlights
1.1 Lumped vs. distributed modelsHydrologic models that commonly are referred to as “lumped-parameter” or “lumped” models generally have a small number of parameters, each representing a property of the entire hydrologic system; conceptually, many physical processes are lumped into a few parameters
The purpose of this paper is to present a new version of RRAWFLOW with added functionality, to make the code publicly available, and to guide users in its operation
Because the gamma function is asymptotic and has infinite length, system memory is arbitrarily defined in RRAWFLOW as time tm on the impulse-response functions (IRFs) time scale at which 95 % of the curve area is in the range 0–tm
Summary
Hydrologic models that commonly are referred to as “lumped-parameter” or “lumped” models generally have a small number of parameters, each representing a property of the entire hydrologic system; conceptually, many physical processes are lumped into a few parameters. The use of the term “physically based” to describe any hydrologic model, should be discouraged (Beven and Young, 2013) Both distributed and lumped models, have components that can represent different hydrologic processes that can be interpreted in physically meaningful ways (Beven and Young, 2013). The impulse-response function (IRF) estimated in many lumped models represents the physical response to an impulse into the system and provides mechanistic insights into that system, including the peak response time and magnitude and the hydrologic memory of the system (von Asmuth and Knotters, 2004; Beven and Young, 2013; Young, 2013). The choice to use a lumped or distributed model, depends on a study’s objectives and available resources; a lumped model likely is the better choice when it meets the study’s objectives
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