The Water Master is responsible for delivering water from the Big Wood River to each of the three main canals of the delivery system. The Water Master operates the diversion headgates and changes the amount of flow into the three main canals and other smaller ditches to ‘balance’ the water flows throughout the system for delivery of all water rights.

The start of water delivery can be variable depending upon spring thaw conditions, but typically begins April 15th. Idaho Water District manages water delivery from the Big Wood River into the district canal. The amount of water delivered from the depends upon the total active water rights within the two sub-districts and the availability of water all water rights have an origination or ‘priority date and are activated together at the beginning of the irrigation season, and then ‘cut’ as the water resource diminishes, typically in mid-summer. Idaho Water District 37 determines the date of each cut and the ‘depth’ or priority date, to which the cut will be made. The decision is based on water available in the river measured at the Hailey flow meter in the river.  Those with ‘junior’ priority dates are cut earlier than those with ‘senior’ (older) priority dates.

There are other factors besides water availability in the river that can impact water delivery. Water lost between the source (the river) and the user is referred to as ‘ditch losses. It is water that either sinks through the sides and banks of the ditch or is lost due to evaporation. Ditch loss is highly dependent on weather, ditch integrity, or condition, and amount of flow. A simple principle dictates that the more water there is, the easier it is to deliver. In other words, it takes water to move water.

Ditch loss becomes much more significant later in the irrigation season when the weather is hot and dry, the banks are hot and dry, and water required by senior right holders reduces the availability for smaller and junior water rights. The end of water delivery is variable from season to season and is highly dependent upon the water right priority date.