# Fill Sinks XXL (Wang & Liu)

Copyrights (c) 2007 by Volker Wichmann
This module uses an algorithm proposed by Wang & Liu to identify and fill surface depressions in digital elevation models.
The method was enhanced to allow the creation of hydrologic sound elevation models, i.e. not only to fill the depression(s) but also to preserve a downward slope along the flow path. If desired, this is accomplished by preserving a minimum slope gradient (and thus elevation difference) between cells.
This version of the module is designed to work on large data sets (e.g. LIDAR data), with smaller datasets you might like to check out the fully featured standard version of the module.
References:
Wang, L. & H. Liu (2006): An efficient method for identifying and filling surface depressions in digital elevation models for hydrologic analysis and modelling. International Journal of Geographical Information Science, Vol. 20, No. 2: 193-213.

## Parameters

Grid system
Grid system
  Grid system
DEM
Input Grid
  Digital elevation model
Filled DEM
Output Grid
  Depression-free digital elevation model
Minimum Slope [Degree]
Floating point
  Minimum slope gradient to preserve from cell to cell; with a value of zero sinks are filled up to the spill elevation (which results in flat areas). Unit [Degree]