Before you can set a budget for your pond liner and heavy machinery costs, you’ll need to know the approximate size of the pond. Ponds are measured by acre, much like any other type of land, but they’re also rated by a measurement known as an acre-foot. This refers to the amount of water required to cover an acre of pond space in a one-foot deep layer of water. Knowing how many acre-feet you’re going to create by building a pond of a specific depth and surface size is essential to determine if the pond will supply enough irrigation water or space for fish. Each acre-foot supplies a total of 325,851 gallons of water for you to use, so even a quarter acre-foot pond can satisfy many agricultural and recreational needs.
Calculating the amount of water needed for keeping livestock watered is relatively easy. There’s an established range of water consumption for each type of livestock, such as the 12 to 15 gallons of water consumed daily by cattle. When you need excess water for cleaning stalls or processing in meat and dairy facilities, add at least 20 to 30 gallons per head of cattle. Check husbandry manuals for other livestock to estimate how many gallons per head you’ll need for your flock, herd, or sounder.
Irrigation needs are estimated at the gallons per acre per inch of water. For example, it takes over 27,000 gallons of water to supply an acre with just a single inch of water. Check the inches of water required per week by your crops, multiply that by your acreage, and you’ll know how many gallons the pond must supply per week.
Regardless of use, ponds must be sized large and deep enough to overcome the natural evaporation loss of your area. The USDA provides charts of average evaporation amounts for all parts of the country, making it easy to determine what you’ll lose per month or year. Shallow water evaporates significantly faster, so keep the water a minimum of two to three feet deep throughout the entire pond to limit water loss.