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Dominant Irrigation Type on Cropland, 1997

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This polygon map shows the dominant irrigation type for irrigated cropland by hydrologic unit. The available water sources are categorized by 1) gravity 2) pressure, and 3) both pressure and gravity.

Cautions for this Product:
In many areas shown on this map as irrgated, non- irrigated cropland may be more common than irrigated cropland. Total amount of irrigated cropland may be small.


Source: National Resources Inventory, 1997
Distributor: USDA-NRCS-RIAD
NRI sample data are generally reliable at the 95% confidence interval for state and certain broad substate area analyses. Generally, analyses that aggregate data points by smaller geographic areas and/or more specific criteria result in fewer data points for each aggregation and therefore less reliable estimates. NRI maps reflect national patterns rather than site- specific information.


Aggregate Layer: 8 Digit Hydrologic Unit Areas with Federal Land Other Layers Displayed: States, Rivers


Gravity and pressure irrigated:
Farm delivery and field distribution of irrigation water is a combination of gravity and pressure facilities. For example, a valve is used to reduce pressurized water delivered to a farm or field for subsequent distribution by a gravity surface irrigation system. [NRI-97]

Gravity irrigated:
Water is delivered to the farm and/or field by canals or pipelines open to the atmosphere; and, water is distributed by the force of gravity down the field by: [NRI-97] 1. A surface irrigation system (border, basin, furrow, corrugation, wild flooding, etc.) or, 2. Sub- surface irrigation pipelines or ditches.

Hydrologic units:
A hierarchical system developed by the U.S. Geological Survey that divides the United States and the Caribbean into 21 major regions, 222 subregions, 352 accounting units, and further subdivided into 2,150 cataloging units that delineate river basins having drainage areas usually greater than 700 square miles. [USGS]

Irrigated land:
Land that shows evidence of being irrigated during the year of the inventory or during two or more years out of the last four years. Water is supplied to crops by ditches, pipes, or other conduits. Water spreading is not considered irrigation; it is recorded as a conservation practice. [NRI-97]

Pressure irrigated:
Water is delivered to the farm and/or field in pump or elevation induced pressure pipelines; and water is distributed across the field by: [NRI-97] 1. Sprinkle irrigation (center pivot, linear move, traveling gun, side roll, hand move, big gun, or fixed set sprinklers), or, 2. Micro irrigation (drip emitters, continuous tube bubblers, micro spray or micro sprinklers).

Product Information

Product ID: 5306
Production Date: 1/27/00
Product Type: Map

For additional information contact the Resources Inventory and Assessment Division. Please include the Product ID you are inquiring about. or 1400 Independence Avenue SW - P.O. Box 2890 - Washington D.C. 20013. If you use our analysis products, please be aware of our disclaimer.