Priority Counties for Rainwater Harvesting on the Ogallala Aquifer, Texas

Because each of the four maps for governance and surface water were rendered in boolean format it was possible to combine them into one 'unsuitability' map that displayed areas less likely to need a rainwater harvesting program based on these four factors. Reclass and the Add function in Overlay were used to generate this map, which output a separate numeric value for each combination of factors. Each of the factor combinations was then assigned a value of importance between 0-255. see map

Reclass #	Combination of factors present	New Suitability Value
6	IBTs	255
2	GCDs	220
8	GCDs + IBTs	215
1	PGMAs	190
3	PGMAs + GCDs	180
10	SW	70
16	SW + IBT	65
12	SW + GCDs	40
18	SW + IBT + GCD	35
11	SW + PGMAs	20
13	SW + PGMAs + GCDs	0

Key: Interbasin Transfers (IBTs), Grounwater Conservation Districts (GCDs), Priority Groundwater Management Areas (PGMAs), Surface Water (SW).

Interpretation

Areas that only contain IBTs were considered most suitable for rainwater harvesting (most in need of water conservation) because the IBTs are only proposed transfers that may or may not come to fruition. In addition, IBTs affect only small areas relative to the other criteria. GCDs were also ranked as highly suitable, not because they are ineffective, but because PGMAs and SW have a far greater impact on water conservation. Areas that contained a combination of SW, PGMAs and GCDs were ranked as least suitable (suitablity value of 0) due to the high potential in these areas to conserve groundwater. Some combinations were not present, for example the combination of all four factors (SW, PGMAs, GCDs and IBTs) did not occur anywhere within the Ogallala counties. Combinations that were not present were not included in this table.

Priority index based on governance and surface water factors

Cartographic model used to obtain suitability map