SDR output potentially undervalues wetlands

Hi Nat Cappers,

I generated an SDR output but am concerned that the sedimentation retention index wetland values are so low and that slope seems to be driving the model. Does the attached look reasonable?

Thanks for having a look.


Hi David -

Slope is indeed a big driver of the results of the model, but of course it’s not the only factor. One thing to remember with the sediment retention output is that it is not actually quantifying (or even indexing) the amount of sediment retained on that pixel, based on what comes at it from upslope. It is only showing the difference between the current land cover type versus bare ground, not taking upslope erosion into account at all. (See the related section in the User Guide for a little more info on this.)

If you want to get a better idea of how well wetlands retain sediment, I’d suggest doing a scenario where the wetlands change to some other plausible land cover type (agriculture, development or whatever), then looking at the difference in sediment export. The areas upslope of the wetlands will likely show significantly less sediment export with the wetlands than without.

I do believe that the software and hydrology teams are working on a way of actually quantifying sediment retained from upslope, but that is not part of the model yet.

~ Stacie

Many thanks for the quick and most illuminating reply Stacie. Yes, a scenario exercise demonstrated a pronounced impact on wetland sediment export.