Diversion-Runoff Calculator User Manual

Most tunable parameters in the Diversion-Runoff Calculator (DRC) relate to the efficiency of the irrigation system. Default parameter values are initially set based on a variety of information sources and can be adjusted as more information becomes available. The following are the efficiency parameters:

The DWRi Distribution Network provides an attribute in their NetFlowlines.shp file that specifies whether a canal is lined, unlined, or piped. The ec value is assigned according to the lining attribute. Currently, ec = 0.95 for lined canals and pipes.  Unlined canals have ec = 0.8.

This is the percentage of water that goes to adjacent fields. It is initially set to 0.2 in keeping with what Cruff and Hood (1976) found for Grey Mountain / Rocky Point Canals. 

This is the percentage of water that goes to adjacent canals. It is initially set to 0.4.

This is the maximum fraction of main canal diversion that can be lost to seepage by the main canal or the sub-canals. This term simply provides a limit on seepage so that long canals do not loose all their water to seepage. We keep the seepage rate to less than 0.2, which is what Cruff and Hood (1976) found for Grey Mountain / Rocky Point Canals. 

The ea term estimates the efficiency associated with a given irrigation practice. These values are assigned based on values from the 'Irrigation Conversion Water Savings Destination Calculator' from the Utah State University Extension Office.

Note: Parameter values can be changed in the DRC python code under the “Set_Irrigation_Efficiency_USU_Calculator” function.

Lc values for each canal are obtained from DWRi geospatial datasets (DWRi, 2023b). 

Xc accounts for seepage (loss or gain), evaporation from the water surface, and transpiration from canal vegetation. For canals known to use pipes (Rhoades Canal, WPPBB Pipeline, Shanks Pipe) as well as those suspected of using pipes based on satellite imagery (Knight Canal and Jones Ditch), Xc is set to 0. In earthen canals, the majority of canals in the test basin, Xc is difficult to quantify and can be negative (seepage) or positive (gaining) depending on the location of the canal and the groundwater table (Cruff & Hood, 1976). The Rocky Point Canal and the Grey Mountain Canal are two of the longest earthn canals within the test basin. Based on Cruff & Hood (1976), Xc for the Rocky Point Canal is set to 0.003 m3/s per km of canal (0.185 ft3/s per mile of canal), and 0.014 m3/s per km of canal (0.807 ft3/s per mile of canal) for the Grey Mountain Canal. The user can set Xc values for each canal, which may be a calibration parameter in future efforts. Here, we set  to 0.009 m3/s per km of canal (0.496 ft3/s  per mile of canal) for all other canals (average of the Xc values for Rocky Point and Grey Mountain Canals).  The Xc values reflect the canal losses after the canal has been charged, meaning it does not account for the losses of water at the onset of the irrigation season when the canal is initially being filled with water. 

Note: Values for Xc can be changed under the “Calculate_Canal_Loss” function.

Canal losses (denoted as Xc) represent the combined effects of seepage (loss or gain), evaporation from the water surface, and transpiration by canal-side vegetation. The value of Xc varies depending on the canal’s construction and local hydrologic conditions.

For canals known or suspected to be piped—either through infrastructure records or verified via satellite imagery—Xc is assumed to be zero. In contrast, for earthen canals, seepage and vegetation losses can be significant, and in some cases, losses may be negative (i.e., canals gain water from shallow groundwater tables), depending on subsurface conditions (Cruff & Hood, 1976).

Rather than assigning a uniform value for all canals, the DRC now uses a catalog of published loss rates for selected canals. For each named canal, the catalog stores flow rate, flow loss, and segment length, from which the program computes:

• Absolute loss rate per unit length (Xc, in m³/s per km),

• Proportional loss per unit flow per km, and

• Percent loss per km.

If a canal’s name matches one in the catalog, its published loss rate is used. For canals not listed, median values derived from the catalog are applied, providing a representative estimate.

Example calculation for a catalog entry:

For each canal in the model:

1. The code checks if the canal has a known loss rate in canal_loss_catalog.

2. If so, the corresponding published value is used.

3. If not, the median values across all cataloged canals are used as defaults.

The final daily loss is computed as:

This method assumes canals are already charged with water—initial filling losses are not included in this estimate. Current loss rates are based on published values for six Utah canals (namely Rocky Point A Canal, Grey Mountain Canal, Carbon Canal, Green River Canal, Thayn Canal, East Side Canal) according topublished values from the following sources:

Note: Additional published values for Xc can be added to the “canal_loss_catalog” dictionary in the DRC code. Here the user can explicitly assign the loss rate for a specific canal if known.