How to find Q in m3/sec from a raster having Q in mm for hydro power calculation

Question

I am having a raster file with runoff depth Q in mm which was obtained from SCS method.

I want to calculate hydro power potential at any location on my DEM. In the formula Q is in m3/s but we are getting Q in mm from SCS method. Is there any tool/script/software dealing this? How to find Q in m3/sec from a raster having Q in mm for hydro power calculations?

I am using arcgis (9.3 and 10).

Answer 1

I don't know of a specific tool to perform the conversion you are looking to do, but I would guess that it should be relatively straightforward to calculate (please check my math).

1. Get your units converted to cubic meters. Your raster file has an area associated with each grid - use this area to multiply your mm of water to get volume. For example, if your grid cells are 100m x 100m (10,000 square meters), you first would convert your Q from mm to meters: Q in mm = 0.001 Q in m. Now you can multiply Q in m by the area to get your volume: 0.001m * 10,000m2 = 10m3
2. Convert your time units. Your data should have some specified time period associated with them (Q in mm per sec/day/month/year/etc.). If your time units are per second and you need per day, your conversion factor is 60*60*24 = 86,400 seconds per day.
3. Convert to Q in volume/time. If your grid cell size is 100m x 100m and your time units are seconds, you can convert to cubic meters per day: (10m3/sec)*86,400 sec/day = 864,000 m3/day

This can all be done using the raster calculator tool.