Other Sources of Data for Watershed Model Comparison
MDE TMDL Data
The data used in the following comparisons were collected to assist Maryland Department of the Environment in their development of TMDLs. The data were collected such that two seasons were captured. For most basins, three collection dates were chosen during the spring that normally correspond to higher flows. Three dates were also chosen during the summer months which are normally low flow periods.
There are many differences between the output of the watershed model and the data. The watershed model simulates the years 1984 through 1995, while the data were collected after that period. The watershed model simulates land use nutrient export only, without in-stream processes, while the data were collected in waterways. The watershed model is designed to simulate loads, while the data are in concentration. The watershed model simulates watersheds and collections of watersheds that are roughly equivalent to 8-digit USGS HUCs. The data are generally from much smaller areas.
To make a comparison between the watershed model and the data, the following procedure was developed:
The data and watershed model output were each aggregated into major basins: Choptank, Nanticoke, Pocomoke, etc.
The watershed model output was aggregated temporally using a seven-day moving average to simulate in-stream mixing.
The data and watershed model concentrations were plotted on as time series using concentration vs day-of-year.
In each plot, the blue dots are watershed model output and the magenta dots are observed concentration. Generally, the results were very satisfactory given the limitations of the comparison.
The results are given here in Adobe Acrobat format:
Total Nitrogen
Total Phosphorus
Patuxent Data
DNR and MDE have also made available some patuxent data for stations above the fall line at Unity and Savage and several points below fall line.
The same method as the Eastern Shore was used to compile these data, however the agreement is not as good. The difference can probably be attributed mostly to the presence of point sources in the Patuxent, which are not prevalent on the Eastern Shore.
Total Nitrogen
Total Phosphorus
BACK
last updated 8/2/2000