Models

Models

The human interaction with the natural environment through catchment management has changed the environment considerably. The need has grown to foresee the impact of human actions on streams and catchments. Altering catchment attributes inevitably impacts in-stream processes in a cause-effect chain.
Integrated modelling tools should depict these dependencies on variable scales and simulate parameters like

  • water quality and quantity,
  • flow velocity distributions,
  • erosion,
  • sediment transport and
  • aquatic habitat suitability.


Additional model requirements are user friendliness, robustness, future-proof through constant development, availability in the public domain and usability in a GIS (Kiesel et al. [4]).

(click to enlarge)

The figure shows the SWAT, HEC-RAS and AdH application in a modelling cascade. On the right, the simulated impacts and the depicted processes on different scales are explained. It is important to note that the output of each model is the input to the next model on the smaller scale. Figures a-d show the spatial scales on which the models are applied. (a) shows the SWAT model domain with the catchment, the subbasins (numbers 1 to 17) and the stream network. (b) shows the HEC-RAS model domain with the cross sections and the tributaries from the stream networtk. In (c), the AdH model domain is shown, which is defined by a triangular surface mesh. For the red rectangle, a detailed part of the triangular element mesh with substrate boundaries is shown in (d).

Ecohydrological model SWAT

The Soil and Water Assessment Tool (SWAT, Arnold et al. [1]) is a river basin scale model developed to quantify the impact of climate and land management practices on the hydrologic cycle in large, complex watersheds.
SWAT is a public domain model actively supported by the United States Department of Agriculture(USDA) Agricultural Research Service (ARS) at the Grassland, Soil and Water Research Laboratory in Temple, Texas, USA. The model and its GIS interface (Winchell et al. [8]) are used world wide (Gassman et al. [3]) and are continuously under development. SWAT depicts different physical processes that are governing water and particle fluxes on the catchment- and reach scale. Land use changes, discharge regime, impact of drainages, groundwater levels, urban or rural water quality and climate change can be dealt with on various catchment sizes for time scales of days to decades. SWAT has a long history of application at the Department of Hydrology and Water Resources at Kiel University (Schmalz and Fohrer [5]).

For more information please have a look at the SWAT website

One dimensional (1D) hydraulic model HEC-RAS

The Hydrologic Engineering Center (HEC) in Davis, California developed the River Analysis System (RAS) to aid hydraulic engineers in channel flow and floodplain analysis.
The U.S. Army Corps of Engineers (USACE) Hydrologic Engineering Center River Analysis System (HEC-RAS, USACE [6]) with its GIS interface HEC-GeoRAS (USACE [7]) is utilized by major water related administrations, universities and engineers worldwide. HEC-RAS is a public domain model that includes numerous data entry capabilities, hydraulic analysis components, data storage and management- as well as graphing and reporting capabilities. Thus, it has found wide acceptance since its public release in 1995. For depicting spatially explicit in-stream processes at cross sections along river reaches, 1D hydraulic models are suitable tools. They are capable of calculating hydraulic flow properties like velocities, depths and shear stress, sediment erosion and deposition on small streams up to complex river systems in reasonably fast computation times. However, for depicting the dominating processes on broad and short river sections or to assess seamless, small scale hydraulic impact on substrates, two-dimensional hydraulic models are more suitable.

For more information please visit the HEC-RAS website.

Two dimensional (2D) hydraulic model AdH

The USACE Engineer Research and Development Center (ERDC) in Vicksburg, Mississippi, has developed Adaptive Hydraulics (AdH, Berger et al. [2]), a model that is capable to depict hydraulic flow processes.
AdH is a flexible public domain model which can describe both saturated and unsaturated groundwater, overland flow, 3D Navier-Stokes and 2D and 3D shallow water problems. Key advantages of the model are the automatic adaptation of mesh resolution and time steps during model runs and the fully MPI parallelized code which runs on both Windows and UNIX-based multi-processor machines. SWAT and HEC-RAS can supply boundary conditions to AdH which enables a connection from the catchment scale to the small-scale reach scale. AdH is used to simulate the impact of stream properties, upstream hydraulics on velocities and water depths as well as erosion and deposition of sediments in high resolution on selected stream sections.

For more information please have a look at the AdH website

Further description on the three models can be found in Kiesel et al. 2012 [4]

For large-scale applications we plan to use data obtained from the Watergap model
and species distribution models as provided by Biomod

References

[1] Arnold J.G., Srinivasan R., Muttiah R.S. and Williams J.R. “Large area hydrologic modelling and assessment part I: model development”, Journal of American Water Resources Association, Vol. 34, No. 1, (1998), pp. 73-89.
[2] Berger R.C., Tate J.N., Brown G.L. and Savant G. “Adaptive Hydraulics – A two-dimensional modeling system”, AdH v4.202, USACE CHL-ERDC, (2013).
[3] Gassman, P. W.; M. R. Reyes; C. H. Green; J. G. Arnold (2007). The Soil and Water Assessment Tool: Historical Development, Applications, and Future Research Directions. Transactions of the ASABE 50 (4): 1211–1250.
[4] Kiesel, Britta Schmalz, Gaurav Savant, Nicola Fohrer (2012) ACROSS THE SCALES: FROM CATCHMENT HYDROLOGY TO INSTREAM HYDRAULICS. 10th International Conference on Hydroinformatics HIC 2012, Hamburg, GERMANY. 8 pages.
[5] Schmalz B. and Fohrer N. “Comparing model sensitivities of different landscapes using the ecohydrological SWAT model“, Adv. Geosci., Vol. 21, (2009), pp. 91-98.
[6] USACE. “Hydraulic Reference Manual”, Version 4.1, US Army Corps of Engineers, Hydraulic Engineering Center, (2010).
[7] USACE. “HEC-GeoRAS, GIS Tools for Support of HEC-RAS using ArcGIS”, User’s Manual, Version 4.3.93, (2011).
[8] Winchell M., Srinivasan R., DiLuzio M. and Arnold J.G. “ArcSWAT Interface for SWAT2012”, User’s Guide, Blackland Research Center, ARS Temple, Texas, (2013).