Diversion-Runoff Calculator User Manual

The DRC can be used to compare the effect on water demand due to landuse changes and the implementation of different irrigation practices. Users can change canal linings, crop types, irrigation practices, and can also reclassify landuses or fallow individual fields to understand how changes to the system affect water use and demand. The user can also artificially constrain the irrigation season by specifying start and cut-off dates. The DRC lets the user see how changes on the ground might effect the diversion demand and traces these changes back to the water rights for more sophisticated crediting and accounting.

Edit Individual Fields and Canals

When populating the ESRI geodatabase with GIS layers using the UCRAF ArcToolbox several new fields are added to the water related land use (WRLU) and Flowlines feature layers as follows: 

These fields are read in lieu of the original WRLU (Description, Label, & Landuse) and Flowline (Lining, FlowlineTy) attributes when a change case scenario is specified in the input file:

These new fields are initially populated with the original WRLU (Description, Label, & Landuse) and Flowline (Lining, FlowlineTy) attributes to match the base case yielding DRC results identical to the "Base Scenario" unless individual attributes are modified. Split Start/End date fields are added to constrain irrigation between certain calendar dates, irrespective of the irrigation season and crop water demand.

The user can select individual fields or canals within their respective feature layer and give them different characteristics in order to see how changes affect the net irrigation water demand and associated water rights. This can be done on the basis of an individual field or canal by clicking on an attribute and selecting from the drop down menu as shown below, or alternatively, by performing a bulk edit on a selection using the Field Calculator function in ArcGIS. 

A calendar picker is used to adjust the start and end dates for split irrigation seasons as shown below:

Similarly, a canal lining change is made by editing the attributes in the 'Flowlines' attribute table:

Change Case Output

Changes to the crop type, irrigation method, application season, and canal lining affect the water demand and application efficiency resulting in changes to the net irrigation water requirement. Fallowing fields altogether eliminates the demand and could potentially reduce the length of the distribution system if the field is located at the end of an irrigation run in which case the canal length may need updating ('New_Len'). The DRC accounts for all these changes when computing water demand. It also associates the changes with the affected water rights. 

Running a change case scenario produces its own separate set of output files along with a change log that tracks changes in terms of acreage and canal length for each main canal service area. The additional change files are highlighted below as they appear in the working directory. Output associated with the change case generally as the  '_ChangeCase' suffix appended to the file name to avoid any confusion with, or overwriting of, the base run.