A water rights engineer is generally required for augmentation plans, substitute water supply plans, subdivision water supply plans, and changes of water rights.
Water Requirements: For the three types of new plans listed above, the engineer starts the analysis by estimating the water requirements for the plan. The water requirements for subdivisions typically are based upon the number and size of the homes to be built, commercial buildings, the lawn areas, water features, ponds, and sewer systems. Climatological data is used to determine water needs for the lawns at the given location and elevation and to estimate pond evaporation.
Stream Depletions: If wells are used to provide water, the engineer must determine the river or stream depletions that will be caused by pumping from the well. In overappropriated systems (most of Colorado), depletions caused by direct diversions or from well pumping must be offset by replacement water because they cause injury to senior water rights. The lagged stream depletions from wells are usually calculated by computer modeling based upon factors such as soil transmissivity, storativity, distance to the stream, and the distance to a no-flow boundary.
Return Flow Credits: The type of lawn sprinkler system is important to determine the efficiency of the irrigation so that the portion of water not consumed by the grass can be calculated as a return flow credit. Likewise, the efficiency of the sewage system is used in the analysis to calculate the credit from septic returns.
Replacement Water: Replacement water can be provided from many sources including upstream stored water and from other purchased water rights. In most cases, the purchased water right must be changed to the new use, or new place of use, in water court. For example, agricultural water rights are frequently used for new replacement water use. The engineer will calculate the historical consumptive use of the water right based upon the irrigation water requirement of the crop type and historical diversions of water under the water right. Factors such as the latitude, average mean temperatures, average precipitation, crop type, elevation, and soil type are used to determine the irrigation water requirement. Comparisons are made between the historical diversions and irrigation water requirement to compute the historical consumptive use credits that can be obtained from the water right. Another important aspect of a change of water right is that the historical return flow must be maintained in the future after the change takes place. Therefore, the engineer will calculate the historical return flow obligation and ensure the water accounting factors in this obligation in the change of water right.