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USGS Fact Sheet FS-080-97
by Moon H. Kim and James C. Ebbert
October 1997


During 1993-94, scientists with the U.S. Geological Survey National Water Quality Assessment (NAWQA) Program collected samples of surface-water discharges at the outflows of nine drainage basins containing irrigated cropland. All or parts of the drainage basins lie within the Quincy and Pasco Basins of Washington State. The study area is defined by the boundaries of the Columbia Basin Irrigation Project where irrigation water is diverted from the Columbia River and distributed to cropland through an extensive network of canals and laterals. Samples were analyzed for concentrations of suspended sediment, pesticides and nutrients. Usually, the effectiveness of an irrigation method in reducing surface runoff is assessed with small-scale studies on plots and fields. The data from this NAWQA study provided an opportunity to assess the effects of the two dominant methods of irrigation, furrow and sprinkler, on the runoff of soil, pesticides and nitrogen from irrigated cropland to surface waters at a drainage-basin scale. Using historical data, the relation between changes in methods of irrigation and changes in soil loss over time was also evaluated.

[Map of land use in study area and sampling sites] Land use and sampling sites (GIF, 33173 bytes)

Irrigated agricultural drainage basins sampled in the Quincy and Pasco Basins

[mi2, square mile]
Site					Drainage   Irrigated	Furrow
abbrevi-			 	area	   area		irrigation
ation	  Sampling site			(mi2)	   (mi2)	(percent)
CCL000	  Crab Creek Lateral	  	   56.2	     39		  44
E68001	  EL68D Wasteway		a 146	     52		  78
ESQ005	  Esquatzel Wasteway	 	a 475	     72		  14
FRC006	  Frenchman Hills Wasteway  	  202	     80		  27
LCC005	  Crab Creek near Beverly	  386	     93		  43
LIN008	  Lind Coulee Wasteway	 	a 703	     35		  58
MAT001	  Mattawa Drain		   	   18.1	     13		   0
P16000	  PE16.4 Wasteway		  118	     44		  19
SAN004	  Sand Hollow Wasteway	   	   46.5	     31		  22

a = Parts of drainage areas extend outside the study area.

How Does Irrigation Affect Surface-Water Quality?

Surface-water quality is degraded by the runoff of soil, pesticides and nutrients from cropland to streams. Runoff of soil and associated compounds from cropland typically increases when surface runoff increases as a result of precipitation or irrigation. Sprinkler irrigation usually produces less surface runoff than furrow irrigation. Therefore the use of sprinkler irrigation reduces the runoff of soil and may reduce the runoff of pesticides and nutrients from irrigated cropland and their transport to surface waters.

 o Decreasing Use of Furrow Irrigation Results in Less Soil Loss

Analyses of samples collected from nine drainage basins during April and May 1994 at the beginning of the irrigation season indicate that yields (amount discharged divided by acre of irrigated cropland) of suspended sediment, an indicator of soil loss, are closely related to the percentage of cropland irrigated by the furrow method.

[Graph of suspended sediment yield and fraction of crop irrigated by the furrow method]

 o Downward Trend in Use of Furrow Irrigation Over Time Has Decreased Soil Loss

Analysis of long-term data for one site, Crab Creek near Beverly (LCC005), shows a strong relation between yields of suspended solids and the percentage of cropland irrigated by the furrow method. (Suspended solids and suspended sediments are differentiated by the techniques used to collect and analyze the samples. The concentration of suspended solids are usually less than suspended sediment.)

[Graph of suspended solids yield and
fraction of crop irrigated by the furrow method]

 o Decreasing Use of Furrow Irrigation Provides Additional Benefits to Surface-Water Quality

In a related study in the Quincy and Pasco Basins, Gruber and Munn (1996) found that drainage basins with lower percentage of cropland irrigated by the furrow method had lower concentrations of DDT in streambed sediment and fish tissue. To determine if runoff losses (amount discharged divided by amount applied) of other pesticides and nitrogen also relate to the irrigation method, samples were collected and analyzed at two sites during the 1993 irrigation season. Results indicate that runoff losses of most pesticides and nitrogen in the Crab Creek Lateral drainage basin (CCL000), with a lower percentage of cropland irrigated by the furrow method, were less than losses from the EL68D Wasteway drainage basin (E68001) (see following table).

Comparison of runoff losses from two basins sampled in 1993

				Furrow		    Runoff Losses:
				irrigation	Pesticides	Nitrogen
	Sampling site		(percent)	(percent)	(percent)
Crab Creek Lateral (CCL000)	44		a 0.04		5.6
EL68D Wasteway (E68001)		78		a 0.31		8.4

a = Median value of 13 pesticides.

 o Other Management Practices Can Reduce Soil Loss

Although this fact sheet showed the effects of irrigation method on soil loss and runoff losses of compounds, other management practices can also influence soil loss from irrigated cropland. For example, adding polyacrylamide (PAM) to irrigation water increases the cohesiveness of soil particles, making the soil less subject to erosion (Raloff, 1993). Since 1995, PAM has been used extensively on cropland irrigated by the furrow method in the study area.


Gruber, S.J. and Munn, M.D., 1996, Organochlorine pesticides and PCBs in aquatic ecosystems of the Central Columbia Plateau: U.S. Geological Survey Fact Sheet 170-96, 4 p.

Raloff, J., 1993, Holding on to the Earth: Science News, v. 144, p. 280-281.

USGS Fact Sheet FS-080-97
By Moon H. Kim and James C. Ebbert
October 1997
This fact sheet is based on the journal article by Ebbert, J.C. and Kim, M.H., in press, Relation between irrigation method, sediment yields, and losses of pesticides and nitrogen: Journal of Environmental Quality, [about 8p.]

For further information, contact:
Project Chief
1201 Pacific Ave., Suite 600
Tacoma, WA 98402
Phone:(253) 593-6530 ext 2687; -6514 fax

Suggested citation:

Kim, Moon H., and Ebbert, James C., 1997, Irrigation and surface-water quality in the Quincy and Pasco Basins, Washington: U.S. Geological Survey Fact Sheet FS-080-97, on line at URL, accessed [date of access].

For a paper copy of this report, send Email to

Central Columbia Plateau - Yakima River Basin NAWQA Study
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