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I I I I I I I I I I I I I I I I I I I Since the images selected for the comparison were taken in August of both 1989 and 1999, it was possible to make a distinction between center pivot sprinklers that were actively irrigating and those that were not active by the color of the image within the parcel. For comparison purposes, it was assumed the circular parcels that were less red or even gray color in the August images had been used to irrigate wheat that had previously been harvested. The circular parcels that were brighter red color were assumed to be actively irrigating spring crops such as corn. Ideally, interpretation of satellite imagery should also be done in conjunction with site-specific field inspection to verify the satellite imagery. This field inspection could not be done since the Landsat photos were obtained prior to the actual study. However, for general comparison purposes, the satellite imagery and the Baca County Assessor's office both show an increase in the number of acres being irrigated and the crop selections that are being irrigated in the District. The Baca County assessor's office shows 52,900 acres irrigated in 1989 and 106,300 acres in 1999. Data also indicates more water was being used in the District in 1999 than was being used in 1989. 5.2 ESTIMATED WATER USE The ability to determine the amount of water actually being withdrawn from the aquifers depends upon either direct measurement or approximation. Examples of direct measurement include flow data obtained directly from wells that are either equipped with totalzing flow meters or hour meters if the rate of discharge of the well is already known. The approximation method utilizes equations and climatological data to estimate the volume of water required. These two methods can be used together to provide accurate estimates of the overall pumpage for an area. One method of estimating water demand is based upon the Blaney-Criddle method with climatological input data from local sites. The source of the crop coefficients used in the Blaney-Criddle formula are from the "Irrigation Water Requirement Technical Release No. 21 If developed by the USDA's Soil Conservation Service. Two sites within the District, Springfield and Walsh, which have climatological data, were selected for this analysis. Springfield was selected because it has a longer period of data and associated climatological averages than Walsh. Walsh was selected because it is approximately twenty miles east of Springfield making it more centrally located and more nearly the same elevation within the irrigated area of the District. In addition, Springfield is approximately 600 feet higher in elevation than Walsh. The estimated monthly and seasonal irrigation requirements per acre using the Blaney-Criddle method were multiplied by the number of acres of the four major crops being irrigated to estimate the peak monthly demand and seasonal demand to fully supply the respective V-2