The UCRAF-DST combines two tools: the Diversion-Runoff Calculator (DRC), a Python-based GIS tool for computing agricultural water demand, and RiverWare©, a leading software for river and reservoir modeling, water accounting, and water rights allocation. The DRC calculates irrigation needs at the field level and integrates with RiverWare to assess drought mitigation scenarios in Utah's Colorado River Basin. 

DRC Overview

The Diversion Runoff Calculator (DRC) is a geospatial modeling tool developed to estimate irrigation water requirements, field runoff, and canal seepage at field-, canal-, and basin-scales. It serves as a critical component of the UCRAF-DST and is designed to aid in water management and drought mitigation planning. The DRC leverages remotely sensed evapotranspiration data and hydrologic models to quantify irrigation demand, optimize water diversions, and evaluate the impact of conservation measures.

Core Concept

The DRC is built upon a spatially explicit water balance model that integrates hydrologic, geospatial, and agricultural datasets to determine the water required for irrigation and the necessary diversions at various scales. The tool accounts for three primary hydrologic components:

1. Consumptive Use (CU) – The amount of water lost to evapotranspiration (ET) and not returned to the river system.

2. Field Runoff (Rf) – The excess irrigation water that flows from one field to another and can be reused downstream.

3. Canal Seepage (Sc) – The water lost from unlined canals that infiltrates the surrounding soil, potentially benefiting adjacent fields or returning to the river.

By combining these factors, the DRC calculates the diversion requirement (Qc), which is the volume of water that must be diverted from a river or canal to meet crop water demand within the canal service area while accounting for system inefficiencies.

Key Hydrologic Components

Field-Scale Water Demand

At the field scale, the DRC estimates consumptive water use (CU) using remotely sensed OpenET evapotranspiration data and ET Demands effective precipitation estimates. The tool considers field-specific factors such as crop type, irrigation method, and soil moisture availability. The water required at the field boundary (Qf) is calculated as:

where:

• ea = Water application efficiency (varies by irrigation method, e.g., flood vs. sprinkler).

• ei = Irrigation system efficiency (accounts for losses due to soil conditions, wind, and management practices).

• Rf = Runoff received from an upstream field.

• Sf = Seepage gained from nearby canals.

Canal-Scale Diversion Requirement

At the canal scale, the DRC aggregates field-scale estimates to determine the total irrigation demand for all fields served by a given canal. It also incorporates seepage losses from unlined canals. The canal-scale diversion requirement (Qc) is calculated as:

where:

• Sc = Seepage losses along the canal, modeled using Darcy’s Law and empirical seepage studies.

and:

Runoff and Seepage

Calculation of runoff is also an important role of the DRC. Cruff & Hood (1976) estimate that 20% of the water seepage from the Rocky Point Canal and Grey Mountain Canal systems returns to the Duchesne River.  Based on the canal network from the DWRi and a DEM we can calculate the distance and gradient between the Rocky Point Canal / Grey Mountain Canal and the Duchesne River.   For the purposes of the DRC, we use the 20% estimate from Cruff & Hood (1976) to calculate a Darcy flux rate (QDarcy) as:

where:

•  KDarcy = the hydraulic conductivity, 

• A = the cross-sectional area for which flow passes through, 

• dh/dist = the hydraulic gradient (hydraulic head divided by distance water hydraulically drains from the canal to the river).

For our purposes, we assume the flow goes through a single unit of depth, making A equal to 1*Lcd, where Lcd is the length of canal that hydraulically drains to the Duchesne River.  The Hydraulic gradient is calculated using the DWRi canal data and a digital elevation model (DEM). 

For approximating the loss rate we assume that the seepage amount from the canal is proportional to the flow in the canal itself. Therefore, instead of a flow rate, we set QDarcy to 0.2 to solve for KDarcy.  KDarcy = 0.248 for Rocky Point Canal and KDarcy = 0.287 for Grey Mountain Canal.  For all other canals we take the average, assuming KDarcy = 0.267. Four main components of runoff are considered in the DRC:

Seepage from a canal to another canal or river (Sc-->c) 

1. • Lcd is the length of the supplier canal that hydraulically drains to the receiving canal/stream.

   • dh/dist is the hydraulic gradient between the supplier canal and the receiving canal/stream. This is calculated using DWRi canal data and a DEM.

   • In the code, the seepage amount gained within each canal/stream is kept in the variable SHP_CanalGainRateCFS_List.

   • SHP_CanalGainRateCFS_List is later aggregated to the Main Canal or the Major River segments.

Seepage from a canal to a field (Sc-->f) 

1. • Lcd = the length of the supplier canal that hydraulically drains to the receiving field(s).

   • dh/dist = the hydraulic gradient between the supplier canal and the receiving field(s).  This is calculated using DWRi canal data, WRLU data, and a DEM.

   • In the code, the seepage amount for each field is kept in the variable WRLU_ID_SeepageFromCanals.

Runoff from flood irrigation fields back to another canal or river (Rf-->c) 

• Rf-->c = (1-ea)Afield_drain FloodField_2_Canal x f(dist) 

  • Afield_drain is the area of a field that actually hydraulically drains to the canal or stream.

  • 'FloodField_2_Canal' is a parameter initially set to 0.2.

  • f(dist) is a function of distance between the field and the canal. Typically, f(dist) = 1 if dist is less than 15m while f(dist) = 0 if dist is greater than 100m, and then linearly interpolated if dist is between 15 and 100m.

• Rf-->c is only calculated for flood irrigation fields, all others have values of 0.0.

• In the code 'SHP_CanalGainFromFields_List' represents the water that a canal gains from adjacent flood irrigation fields.

Runoff from flood irrigation fields to adjacent fields (Rf-->f)

• Rf-->f = (1-ea)Afield_drain FloodField_2_Field x f(dist)

  • Afield_drain is the area of a field that actually hydraulically drains to the adjacent field.

  • FloodField_2_Field is a parameter initially set to 0.2. 

  • f(dist) is a function of distance between the field and the canal.  Typically, f(dist) = 1 if dist is less than 15m, f(dist) = 0 if dist is greater than 100m, and then linearly interpolated if dist is between 15 and 100m.

• Rf-->f is only calculated for flood irrigation fields, all others have values of 0.0.

• In the code 'WRLU_ID_SeepagePercentFromAdjacentFields' represents the water that a field gains from adjacent flood irrigation fields.

Basin-Scale Diversion Estimation

At the basin scale, the DRC sums all canal-scale diversion estimates to provide a total estimate of water diverted for irrigation across the basin. This aggregation allows water managers to analyze regional water use trends and evaluate the impact of conservation measures such as:

• Lining canals to reduce seepage losses.

• Converting flood-irrigated fields to sprinkler systems to improve application efficiency.

• Implementing field fallowing programs to decrease total water consumption.

Conclusion

The DRC provides a scientifically rigorous, GIS-integrated approach to quantifying irrigation water demand and optimizing water diversions. By leveraging remote sensing data and hydrologic modeling techniques, it offers a practical tool for water managers, policymakers, and agricultural stakeholders to evaluate water conservation strategies and enhance drought resilience. While the model captures key components of agricultural water use, return flows to the river and legal water rights considerations remain external factors that should be analyzed in conjunction with broader hydrologic models such as RiverWare within the UCRAF-DST framework.

Reference

Follum, M., Morgan, B., Dorchester, ; Leland, Adolph, ;, Coors, S. ", Powell, A., Leeflang, B., Wahl, M., & Rayes, J. (2025). Development of the Diversion Runoff Calculator to Estimate Agricultural Water Consumption and Irrigation Diversions at the Field- to Basin-Scale in Northeastern Utah. Journal of Irrigation and Drainage Engineering, 151(2), 04025004. https://doi.org/10.1061/JIDEDH.IRENG-10452.