clips & quotes: Fresh Water Science

FYI… given my previous posting, here is an extremely relevant one by Jerry Monaco, presumably a higher up in WWF.

clips & quotes: Fresh Water Science

HydroSHEDS–global watershed-oriented dataset

I might as well do a little publicity here and write on the work that I myself am doing in the water world. I am currently working temporarily at WWF, a non-profit organization seeking to [insert public mission statement spiel here]. One of the projects that WWF has been funded for (and is the lead organization on) is a dataset and associated tools called HydroSHEDS (HS, found at www.wwfus.org/hydrosheds/). While the website, as of the date of this posting, shows an interesting interactive map of the Amazon River basin, it is really only a demonstration of what HS will be able to produce. I leave it to the reader to explore what HS actually is (by perusing the cited website). My specific role is to systematically review expansive parts (i.e. entire continents) of the latest iteration of the global stream network produced by the SRTM data (our source DEM—see http://www2.jpl.nasa.gov/srtm/ for details) and to make modifications and corrections to the SRTM data based on other existing sources of information regarding known stream flow paths, either by burning or adding sinks (hydrolingo for forcing water to flow in a certain direction and creating stopping points, respectively) as needed.

But what is the real significance of this project? In short, the global effort to map the world not according to political boundaries but to natural ones—i.e. by using geomorphologically and hydrologically determined ecological units—is finally taking shape in a form at a global level that is really usable by environmentalists, environmental planners, conservationists, and policymakers, and in a way that has never before been attempted. One of the most significant outcomes of HydroSHEDS will be the ability to easily determine watershed boundaries in a consistently reliable way at whatever level desired by the user given the constraints of the spatial resolution of the data. For example, WWF itself will (I believe) be using this data to create accurate boundaries and associated maps of freshwater ecosystems, which are determined in large part by differences in stream network connectivity, among other factors. Hydrologists will be able to perform stream network analyses at a global level to assist in determining global patterns of terrestrial water distribution. And anybody will be able to use the data to simply create highly detailed maps of rivers and river networks.

Some of the limitations of HydroSHEDS has to do with the limitations of the more common methods of watershed delineation and stream network modeling. But these can be overcome at a later date. As a wannabe hydrologist I should know what the different network analysis methods and different stream network derivation techniques are, but I am only familiar with the most common ones. One limitation, for example, is that streams can only merge, they cannot diverge. In deltas and braided streams this is obviously not desirable, but for planning purposes it poses no significant hinderance. Areas where this could be a huge concern would be in, for example, the Mekong River delta, where the river splits into the “seven dragons” before spilling into the sea. But again, HS has been produced with global consistency in mind and other models/methods can and should be used in the specific instances where HS is inadequate.