Dominant Irrigation Type on Cropland, 1992
This shaded polygon map shows the dominant irrigation type for irrigated cropland for each 8-digit hydrologic unit. The irrigation types are categorized by 1) gravity 2) pressure, and 3) a combination of pressure and gravity. The dominant irrigation type is defined as the irrigation type that is the most common in that hydrologic unit. Areas with 95% or more Federal area are shown as gray. Areas without irrigated cropland are left white.
Cautions for this Product:
In many areas shown on this map as irrigated, non- irrigated cropland may be more common than any type of irrigated cropland. The total amount of irrigated cropland may be small. Irrigation of land uses other than cropland is not included. Data are not collected on Federal land. Data are not available for Alaska, and the Pacific Basin. Data for Puerto Rico and the U.S. Virgin Islands are shown by 6-digit hydrologic unit.
Source: National Resources Inventory, 1997
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
A Land cover/use category that includes areas used for the production of adapted crops for harvest. Two subcategories of cropland are recognized: cultivated and noncultivated. Cultivated cropland comprises land in row crops or close-grown crops and also other cultivated cropland, for example, hayland or pastureland that is in a rotation with row or close-grown crops. Noncultivated cropland includes permanent hayland and horticultural cropland. [NRI-97]
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]
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.
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]
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]
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 ID: 5953
Production Date: 2/8/01
Product Type: Map
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