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Introduction to WATFLOOD

Data Requirements of WATFLOOD

Compared to other hydrological modelling systems, WATFLOOD can be considered as a data intensive system. The initial development stages of the system (1972-75) coincided with the advent of remotely sensed data to provide land cover and meteorological data. It was immediately apparent that such data could enhance hydrological modelling but the models that existed at the time could not be easily adapted to take advantage of the high spatial and temporal resolution. From the onset, WATFLOOD was designed to incorporate the remotely sensed data in an efficient manner. This led to the gridded format of all data used by WATFLOOD, including discretization of the watershed itself. Thus in WATFLOOD, each "sub watershed" or element is more-or-less the same size. Exceptions occur along basin and sub- basin boundaries to ensure drainage areas at streamflow gauges are preserved. The following table presents an itemized list of the data requirement of WATFLOOD.

It is assumed that each of the data listed in Part I of the Table applies to the non-impervious land cover amounts listed in Part II. For instance, within one element, the elevation and contour density is the same for each cover. Any discrepancies are likely counter acted during the calibration process, because for instance, slope can be traded off to roughness.

Part I - Element Data
Data type Data description Use of data
Elevations The elevation of the streambed at its midpoint in each element 1. Calculated temperture gradients as function of lapse rate

2. Calculate streambed gradients used for storage routing scheme

Element areas Based on grid size and percent of element inside the watershed boundary Determine the volume of runoff based on the depth of runoff
Drainage direction One of 8 directions, points to next element in the river routing sequence Provide the recieving element for water routed downstream
Channel type number Channels are assigned to a class of channel: rough, smooth, vegetated, etc. One channel roughness can be assigned to each class
Contour density Maximum number of countours crossing a line of length equal to a grid side in each element When multiplied by the contour interval and divided by the grid length, yields a measure of the terrain steepness within an element
Number of channels Number of equally sized channels traversing an element Large channels are more efficient than small channels, used to correct the travel time in each element
Routing reach number Elements can be assigned to a series of reaches, more than one element can be assigned to one reach When reach numbers are assinged to elements, the total reach inflow is written to a file allowing routing to be carried out separately, in another program such as DWOPER
Part II - Land cover distribution (note not all land types are applicable in each basin
Data type Data description Use of data
Urban or impervious area Per cent urban or impervious area in each element Used to determine size of impervious GRU in each element
Bare area Per cent bare area in each element Used to determine size of bare GRU in each element
Forested area Per cent forested area in each element Used to determine size of forested GRU in each element
Low vegetation area Per cent low vegetation area in each element Used to determine size of low vegetation GRU in each element
Wetland area Per cent wetland area in each element Used to determine size of wetland GRU in each element
Glacier area Per cent glacier area in each element Used to determine size of glacier GRU in each element
Water covered area Per cent water covered area in each element Used to determine size of water covered GRU in each element



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