1,720,977 research outputs found
A downward approach to identifying the structure and parameters of a process-based model for a small experimental catchment
No full textAn intensive field monitoring programme was conducted in 1998 and 1999 in an 84 ha catchment located on the North Island of New Zealand. The data collected includes six soil moisture patterns, 12 soil moisture time-series, flow at the outlets of two subcatchments of 56 ha and 28 ha, rainfall and other meteorological data. This data set was used in a downward approach to constrain the conceptualisations and the parameters of a terrain-based distributed model, aiming to simulate the spatial and temporal variability of the soil moisture and the flow response observed in the two subcatchments. The principal mechanism producing runoff was assessed by a preliminary data analysis, involving rainfall, flow and soil moisture time-series as well as the simulation of infiltration processes at the point scale. Runoff was identified as being mainly produced by saturation excess across the entire monitoring period, despite the high intensity rainfall observed in that area. The model soil-water-retention parameters were determined from the soil moisture patterns. The other soil parameters controlling the soil transmissivity were determined by calibration against the observed flow in 1999 in the 56 ha subcatchment, accumulated at the daily scale. The analysis of the flow data at the hourly scale illustrated the need for a more complex subsurface transmissivity function in order to produce lateral storm flow with a larger range of celerity. A simple solution was to modify the decay of the lateral transmissivity with the soil moisture content by adding a second component activated only for soil moisture close to saturation. The additional parameters were calibrated against the observed hourly flow in 1999 in the 56 ha subcatchment. The remaining data were used for validation purposes. This data-driven, downward approach to identifying the model conceptualisation and parameters resulted in a model capable of reproducing the observed catchment behaviour while minimising model complexity
On the computation of the quasi-dynamic wetness index with multiple-flow-direction algorithms
Full text linkThe quasi-dynamic wetness index, in its original development, was computed by calculating the travel time along all the possible upslope flow paths on a contour-based terrain network. In more recent applications the same approach has been extended to gridded digital elevation models with single-flow-direction algorithms. Multiple-flow-direction algorithms, although more effective in representing flow paths, have not been used because they are not practicable with the established methodology. We propose an alternative method for computing the quasi-dynamic wetness index based on the numerical integration of the linear-kinematic wave equation. This method can be applied to any of the terrain-based flow-direction algorithms currently published. The method is robust and efficient
Pre-event Baseflow and Pre-event Soil Moisture as Predictors of Event Runoff Coefficient
No full textOn the definition of the flow width for calculating specific catchment area patterns from gridded elevation data
No full textSpecific catchment area (SCA) patterns are commonly computed on grids using flow direction algorithms that treat the flow as coming from a point source at the pixel centre. These algorithms are all ambiguous in the definition of the flow width to be associated with a pixel when computing the SCA. Different methods for computing the flow width have been suggested, without giving an objective reason. In the few cases where this issue has been specifically discussed, the flow width is derived from subjective analysis and incorrect conceptualizations. This paper evaluates alternative approaches for defining the flow width when computing SCA patterns, by comparing theoretical and computed SCA patterns on sloping planes, inward and outward cones. The performances of the different methods are discussed in relation to two dimensionless parameters: (1) the global resolution, defined as the ratio of a characteristic length of the study area to the grid size and (2) the upslope area resolution, defined as the ratio of the theoretical SCA to the grid size. The optimal methods are identified by specific threshold values of these dimensionless parameters. We conclude that assuming the flow width invariant and equal to the grid size is generally the best approach in most practical circumstances
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