Water Sources - Details and Data

Each mapped field was labeled with the irrigation water source - surface, groundwater or both. Both EPD and SWCC maps of irrigated fields identified the field shape, attaching the permit number(s) of the source(s). New irrigated fields that had clearly linked permitted sources attached were likewise labeled.

EPD supplied a list of permit numbers identifying those that describe a well (G), those that describe a surface source (S), and those that describe surface sources that are refilled or backed up with wells (W). Fields irrigated by wells only were assigned as 100% groundwater, those from surface, 100% surface, and those labeled as ponds backed by wells were assigned 70% from groundwater and 30% from surface water. These later figures were obtained from Ag Water Pumping monitoring of 45 well-to-pond systems. From 1999 through 2004, these monitored systems pumped the equivalent of 70% of irrigation-applied water from their wells.
Using the area weighted withdrawals from fields with identified sources, a withdrawal profile - percent from wells, percent from surface sources - was computed for each county. These varied from those that obtained 100% of irrigation water from streams and ponds to those that relied almost entirely on groundwater sources. Within each county, fields with unknown sources were assigned source ratios that equaled those for known fields in the county.


Last updated 7/14/2009 James E. Hook