# Calculate River Runoff Volume (Q) with GRASS

I want to calculate Hydropower between points at a River. I already created a Rivernetwork and the Accumulationmap (without weighting) with r.watershed. My next Step was to set equivalent points along the River and find out their elevation -> done. So now I want to calculate the Rivervolume for each point (along the River). For this purpose I downloaded Precipitation data.

My Idea was to multiply the Accumulationmap with the Cell Size and the Precipitationmap (Previously, the card was processed that only the outflow remains on each cell (Runoff=Precipitation - Evapotranspiration)). But I´m not sure if that makes sense because the Accumulation says only how much Cells flow in but not which one (and there are Different Runoffs from different cells -> some also negative).

Do you have an idea how I can realize that and calculate the Riverrunoff for the points?

• Calculating runoff from precipitation over a catchment basin is a complicated task. There are many additional factors beyond the drainage area and total precipitation: infiltration, slope, evaporation, manning coefficient, etc. You probably should be looking at models such as HEC-HMS. – Micha Feb 25 '15 at 7:34
• I dont need to calculate the precipitation over a cathcment basin (calculation without basins) because i use a constant infiltration – Tim Feb 25 '15 at 12:09

``````r.watershed elevation="elevation" flow="runoff" accumulation="flow_accumulation" ...