The Peace-Athabasca Delta is the largest freshwater delta in the world. This is where the Peace River, the Athabasca River and Lake Athabasca meet and give rise to the Slave River, which flows north to the Mckenzie River. The PAD is a biologically, climatically, hydrologically, geomorphically, culturally and historically complex and significant environment. The Delta comprises a large part of the southwestern poertion of Wood Buffalo National Park, is one of two Whooping Crane nesting areas, has been critical to the culture and economy of [First Nations] [Ramsar]
This application concerns a unique feature of the PAD, which is the existence of "perched basins," water bodies that have no means of recharge other than precipitation and overland flooding (by ice jams, usually), and no means of discharge other than evaporation. Given the vastness and low relieve of the PAD, it can be extremely difficult to locate the points at which these basins connect during floods, and more difficult still to delineate their catchment boundaries. In fact, the relief of hundreds of square kilometers of terrain within Egg Lake's catchment is within the nominal error of some LiDAR instruments. Egg Lake itself did not flood between 1974 and 1996, and between 1997 and 2014. Basin connectivity is interesting for several reasons [which?]
The application uses the well-known flood-fill algorithm to "fill" basins in a terrain raster, using pre-configured seed points, or seeds derived from the raster minima. Each seed is given a unique ID. For each flood elevation, the raster is filled and each filled area given the seed's ID. When two regions merge, the new region inherits the ID of one of its parents. At each elevation, the application locates points on the perimeter of each basin which are within a configured distance of the perimeter of another basin. These are considered to be candidate spill points.
The application outputs are shapefiles containing the basins and spill points for each elevation, and a raster containing the basins. One use of the spill point data is to delineate the catchment of the basing using, for example, GRASS' watershed alanysis features (e.g., r.watershed).