Gordon E. Grant
Pacific Northwest Research Station
3200 Jefferson Way
Corvallis, OR 97331
Phone: (503) 750-7328
Fax: (503) 750-7329
The watershed is partitioned into grid elements and topographic attributes of each element are obtained, based on terrain analysis. Input data such as precipitation, temperature and solar radiation are adjusted in terms of elevation. Spatial soil and vegetation distribution and logging history are also read in from GIS database and assigned to each element.
Vegetation characteristics such as biomass, tree height, cover density, leaf area index, and root strength are calculated based on the logging history to simulate the vegetation dynamics after cutting or noncutting. In the present version of this model, only clearcutting and partial cutting can be handled and it is assumed a single layer canopy structure.
Two point linear temperature partitioning is used to differentiate the incoming precipitation into rain and snow. A single layer snowpack energy and mass balance model is utilized with finite difference solution to simulate snow accumulation and melt when the incoming precipitation has snow component or there is snow on the ground.
Interception is described as a linear function with leaf area index through the storage capacity. Total evapotranspiration from each element is based on the Penman-Monteith equation and subdivided into three components of evaporation from bare soil and non-canopy substrate, evaporation from canopy and transpiration from canopy.
Subsurface water movement is based on the Dupuit assumption of slope-parallel saturated flow through a limited depth of soil over a relative impermeable layer of parent material or bedrock. Overland flow is assumed only to occur when the ground is saturated. Some exchange between deep groundwater and the subsurface layer is incorporated.
Intercell water movement is modeled with a kinematic continuity equation and combined subsurface and overland flow equation are solved to route water from one element to another.
Landslide occurrence is simulated with infinite slope model using the hydrological results. Upon any slope instability, the possible runout path or debris flow is simulated using the local slope, channel geometry and mass decay function. Sediment transport out off the watershed by streamflow is based on the rating curve to discharge.
Author of the abstract:Jinfan Duan , cf. the main site of CLAWS
Duan, Jinfan, Gordon E. Grant and Chaur-Fong Chen, 1996.
Dynamic integration of GIS and a physically based, spatially distributed hydro-geomorphic model CLAWS, Proceedings of the Third International Conference/Workshop on the Integration of GIS and Environment.
Duan, Jinfan, Gordon E. Grant and Fred Swanson, 1995.
A coupled hydro-geomorphic and ecological model for examining effects of forest cutting on watershed processes, EOS 76(46) : 261.
The relative magnitude of many hydrologic processes operating in natural landscapes are sensitive to topographic position. Indices of these processes can be developed as functions of distributed soil, vegetation and particularly, topographic attributes. Terrain analysis is one of the basic and pre-required steps for further distributed hydrological modeling. Although various models exist, the data structure may be different. Those different data structures (grid, TIN, vector or contour based) have different advantages and disadvantages that may impose limitations according to research goals, computer hardware and the problem itself (Moore et al., 1992).
In this model, although the hydrological and geomorphic process modules are independent of topographical data structure, the grid based data structure is used due to its simplicity and ease of obtaining spatial data. A commercial Geographical Information System software ARC/INFOb is used to accomplish the related terrain analysis of the watershed based on the topographic Digital Elevation Model data and other spatial layers of soil and vegetation characteristics.
The model produce temporal output including the hydrographs at any user indicated pixels, some basin averages such as basin mean soil moisture and mean snow depth, and spatial distributed results which are dynamically linked to ARC/INFOb. The model writes a series of ASCII files such as element flow, soil moisture content, factor of safety, debris flow and snow depth distribution at any time of the simulation as well as Arc Macro Language (AML) files that let users directly display their spatial results in Arc environment.
Author of this abstract:Jinfan Duan