Hello Everyone,
in SWAT HRU definition part, we need to define slope classes,i.e either single or multiple.
I have a mountainous watershed, so I want to use the multiple slope option but I m not clear that in how many classes should it be classified.
Moreover, what should be the thresholds (class upper limit %)for slope classes?
please see the attached fig showing slope stats by swat and slopes calculated separately using DEM
any help will be much appreciated
If you have more slope classes, you have more hru. I think that you must define the step of your slope every 20%. Please define these classes: 0-20, 20-40, 40-60, 60-80, 80-100.
***Please pay attention that the model uses slopes classofication for calculating CN.
Note, there is an extreme difference between slope in % ( which I am used to) and slope in degrees. The slope classes we used sometimes were more or less as suggested. However at times we customized the slope classes to mirror best management practices or equipment, or reading limits. Sometimes a low slope category might b used to help identify wetlands or riparian areas. We typically might consider using skidders to log trees on up to 35% slope, unless the skidders had cables and we might allow up to 45%, depending on the terrain. Various types of high lead or suspended cable systems on steep slopes. Road Construction costs and soil stability become much higher and with more impact on steep slopes, so important to be able to identify these more critical areas. The nice thing with GIS or ARCMAP, one could make more than one map with varying slope categories to separate out limits on farming, logging, reading, etc. When using the categories within a model as SWAT, you probably need to stick within the limits and intent of the model, so the uniform slope breaks are probably a more likely intent. If using degrees, uniform categories 10 degrees would probably make sense In mountainous terrain. 45 degrees equals 100% slope, and it is very difficult to consider management activities on these extreme slopes, unless describing mountain and cliff climbing opportunities.
Misspelled — reading comments should be roading— my computer thinks it knows what I mean — not always so.
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