The paper deals with the introduction of a new topographic index, i.e. an indicator of water table depth in a hillslope.
We need a simplified index for this job, since we are required to analyze large dataset at large resolution (i.e. an entire basin of thousands of square kilometers, or so, at 1 m or so of resolution). This is obviously an issue since many years, and many researchers tried to get solutions.
The first is the one based on the topographic index (TWI in our paper) by Beven and Kirby (1979), but also by O'Loughlin (1986), and used both in rainfall-runoff models (i.e. TOPMODEL) and hillslope stability analysis (i.e SHALSTAB, 1992 and 1994 and SINMAP, 1994). This index, is laregely applied (for instance in D'Odorico and Rigon, 2003, and in our software Peakflow, named after one other paper mentioned in this blog) but reveled insufficient mainly for three reasons:
1 - Barling and Grayson (1994), on the basis of kinematic concepts showed that seldom rainfall are long enough to bring a hillslope to the stationarity condition which is at the base of the derivation of the TWI. -
2 - Donwhill conditions count, as Jeff McDonnel l, and Jan Seibert, among others, showed in their papers;
3 - TWI also contains the assumption of the identification of topographical gradients with hydraulic head gradients: which is clearly not correct when there are discountinuos or so variations of slope from one pixel to a next-neighbor, since hydraulic potential tends to be continuous by definition.
We introduce here a new index that correspond to the complete perceptual model, and compare it to previous indexes and with simulation performed with a Boussinesq equation solver, used as the truth.
Having such an index would be profitable for rainfall-runoff models like Peakflow, or for modifying models like SHALSTAB and SINMAP in estimating hillslope instability.
Who is interested to know more can ask me or co-authors for copy of the draft.
References of the paper
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