A riparian evapotranspiration package

• Main Authors: Maddock, Thomas, III, Baird, Kathryn J.
• Other Authors: Department of Hydrology & Water Resources, The University of Arizona
• Language: en_US
• Published: Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ) 2002
• Online Access: http://hdl.handle.net/10150/615764; http://arizona.openrepository.com/arizona/handle/10150/615764

A new evapotranspiration package for the U.S. Geological Survey's groundwater -flow model, MODFLOW, is documented. The Riparian Evapotranspiration Package (RIP-ET), provides flexibility in simulating riparian and wetland evapotranspiration (ET) not provided by the MODFLOW-96 Evapotranspiration (EVT) Package, nor by the MODFLOW-2000 Segmented Function Evapotranspiration (ETS1) Package. This report describes how the package was conceptualized and provides input instructions, listings and explanations of the source code, and an example simulation. Traditional approaches to modeling ET processes assume a piecewise linear relationship between ET flux rate and hydraulic head. The Riparian ET Package replaces this traditional relationship with a segmented, nonlinear dimensionless curve that reflects the eco-physiology of riparian and wetland ecosystems. Evapotranspiration losses from these ecosystems are dependent not only on hydraulic head but on the plant types present. User-defined plant functional groups (PFGs) are used to elucidate the interactive processes of plant ET with groundwater conditions. Five generalized plant functional groups based on transpiration rates, plant rooting depth, and drought tolerance are presented: obligate wetland, shallow-rooted riparian, deep-rooted riparian, transitional riparian and bare ground/open water. Plant functional groups can be further divided into subgroups (PFSG) based on plant size and/or density. The Riparian ET Package allows for partial habitat coverage and mixtures of plant functional subgroups to be present in a single model cell. This requires a determination of fractional coverage for each of the plant functional subgroups present in a cell to simulate the mixture of coverage types and resulting ET. The fractional cover within a cell has three components: 1) fraction of active habitat, 2) fraction of plant functional subgroup in a cell, and 3) fraction of plant canopy area. The Riparian ET package determines the ET rate for each plant functional group in a cell, the total ET in the cell, and the total ET rate over the region of simulation.