To download the zipped code for the SCS Direct Runoff module,
right click on the following link and choose "Save Link As..."

SCSperpixel.zip

This file will need to be unzipped in WinZip before it can be compiled.

If you would rather download the code as is
and edit out the characters that get added during file transfer (^M), click here.

Click here to see an example of the SCS Direct Runoff module's output.

....INSTRUCTIONS FOR USE

1. Save the SCSperpixel.cpp code in a directory named "Hydrology" (or whatever you prefer). This directory can contain both this module and the Runoff to Rainfall Ratio module. Compile the code. (On a Sun Solaris 7, an example compile command is "CC SCSperpixel.cpp -o scs". This will generate the output "scs," which is a compiled program ready to run.)
   
   
2. Make sure your ascii landuse files are also in this same directory. These files are the echoes of the original resolution land use maps - NOT the ones resampled to 1-km². You should have created these files following the instructions at the "Data Preparation" link. They should have names such as land87.asc, land96.asc, etc. Your landuse maps must have been based on the following classification scheme: 1=urban, 2=agriculture (bare soil and short vegetation), 3=forest and 4=water.
   
   
3. Be sure that you know the number of columns and rows for the original resolution land use maps. You will be asked to input the number of columns specifically.
   
   
4. Decide if you want to 1) provide detailed soil layers or 2) choose one hydrologic soil group (HSG) that is generally representative of your study site (i.e., A,B,C or D). If you will be providing your own soil layers, you should have one for HSGA, HSGB, HSGC and HSGD. These must have been converted to ascii format (see the "Data Preparation" link) and be at the same spatial resolution as your original land use maps. You should construct these just as if you are preparing another gif image for input to the SLEUTH model. The value in each pixel should be the percentage of the given hydrologic soil group in that grid space. These data layers can be constructed from the conterminous United States dataset that is freely available at http://www.essc.psu.edu/soil_info/index.cgi?soil_data&conus&data_cov&hsg. Once there, click on Datasets.
   
   
5. Decide if you want to use the module's default curve number (CN) table containing values compiled from the literature for mid-Atlantic regions or if you want to input your own CN values. If you choose the latter, you should know the CN value for each hydrologic soil group for the land classes urban, agricultural and forested, as well as the CN value you want to use for water.
   
   
6. Decide on the 24-hour design storm depth you want to use. This should be in inches and is the depth that will be used for every year of runoff prediction in a given module run.
   
   
7. Before running the module, you should note the names of the land use ascii files. There should be one for each year that you want to predict the SCS direct runoff.
   
   
8. Run the SCSperpixel program (just type the name of the program that came out of compiling). All required inputs will be requested through prompts within the module.
   
   
9. For each year of input land use, the direct runoff depth (in inches) will be calculated for the given storm depth on a per-pixel basis. The soils and CN data remain unchanged; the only factor driving possible changes in direct runoff are the transitions in land use.
   
   
10. The output will be both as an ascii file with the raw data and as an ascii file ready for conversion to a gif image. (You will be prompted to provide the names for these files in the module.) For visualization purposes, you can convert to a gif image following the directions at the "Data Preparation" link. Keep in mind that the values in the gif image have been divided by the storm depth (thus scaled to the maximum possible runoff) and multiplied by 100.