Linking a spatially explicit watershed model (SWAT) with an in‐stream fish habitat model (PHABSIM): A case study of setting minimum flows and levels in a low gradient, sub‐tropical river

Abstract

As changes in landuse and the demand for water accelerate, regulators and resource managers are increasingly asked to evaluate water allocation against the need for protection of in-stream habitat. In the United States, only a small number of river basins have the longterm hydrograph data needed to make these assessments. This paper presents an example of how to bridge the conceptual and physical divide between GIS-based watershed modelling of basin-discharge and in-stream hydraulic habitat models. Specifically, we used a Soil and Water Assessment Tool (SWAT) model for the Hillsborough River to produce data for use in a Physical HABitat SIMulation (PHABSIM) model of the same river. This coupling of models allowed us to develop long-term discharge data in ungauged river systems based on watershed characteristics and precipitation records. However this approach is not without important limitations. Results confirm that accuracy of the SWAT-predicted hydrograph declines significantly when either the DEM resolution becomes too coarse or if DEM data are resampled to a coarser or finer resolution. This is due to both changes in the size and shape of the river basin with the varying DEMs and subsequent shifts in the proportions of land use, soils and elevation. Results show the use of 30 m DEMs produced hydrographic patterns amenable for using in-stream habitat protocols like PHABSIM model, especially where little or no hydrographic and land use information exists.

Synthesizing models useful for ecohydrology and ecohydraulic approaches: An emphasis on integrating models to address complex research questions

“…SWAT was developed to assess the effects of land‐use management and climate on water supplies (e.g., nonpoint source pollution) in watersheds, particularly for large catchments (Arnold et al, ). SWAT has also been combined with instream‐flow models to evaluate environmental‐flow recommendations (Casper, Dixon, Earls, & Gore, ). Other hydrology models have simulated the effects of flow alteration on fish assemblages and associated habitat components (e.g., DIVAST, Bockelmann, Fenrich, Lin, & Falconer, and WaterGAP, Verzano et al, ).…”

Integration of hydrological and habitat simulation methods to define minimum environmental flows at the basin scale

“…However, several studies have pointed out the usefulness of the data obtained with rain run‐off models in the EFR studies and particularly in the habitat simulation model (Casper et al . ). The hydrologic data used in the present study come from previous work based on highly detailed hydrologic, climatic and catchment information (García et al .…”

“…Moreover, a 15% loss of WUA is considered sufficient to maintain robustness against natural variability or sampling error (Casper et al . ). Therefore, the establishment of a threshold value of 15% of habitat loss in our procedure meets those requirements.…”

Influence of discharge on fish habitat suitability curves in mountain watercourses in IFIM methodology

“…IFIM is based on the knowledge that most fish species prefer certain combinations of water depths, flow velocities (Ayllón et al, 2010), availability of cover, and bed materials (Parasiewicz and Walker, 2007). IFIM can provide robust assessments of the quality of a river when sufficient data are available (Casper et al, 2011). One of the greatest advantages of IFIM over alternative methods (CCA, RDA, GLM and related-analyses) is the fact that it incorporates spatially distributed model in any desired detail.…”