Powder/Tongue River Basin Water Plan
Technical Memoranda

SUBJECT:	Appendix B Irrigated Crops
PREPARED BY:	HKM Engineering Inc.
DATE:	February 2002

INTRODUCTION

Irrigated agriculture represents, by far, the greatest consumption of water within the boundaries of the Powder/Tongue River Basin planning area. An accurate estimate of existing irrigation water use is therefore central to a comprehensive water use inventory. Estimates of water use by irrigated agriculture can generally be divided into the following three components:

1. Quantity of irrigated lands
2. Types of crops grown and geographic distribution
3. Depth of water consumed by the crops

This memorandum summarizes the methodology used to determine the type and geographic distribution of crops grown on irrigated lands in the basin. The methodology used to map the extent and classification of the irrigated land is summarized in the memorandum "Irrigated Lands Mapping and Water Rights Data" (HKM, 2002). The methodology used to determine the amount of water consumed by irrigated agriculture is summarized in the memorandum "Agricultural Water Use" (HKM, 2002).

The 1972 Water Planning Program report "Water and Related Land Resources of Northeastern Wyoming" summarized the crop distribution for the study area encompassing the Tongue River, Powder River, Little Missouri River, Belle Fourche River, and Cheyenne River (SEO, 1972). Although the crop acreage is not subdivided by drainage, the total acreage and percentages are helpful for the purpose of comparison to the recent estimates. The total crop acreage from the 1972 water plan is summarized in Table 1.

TABLE 1 SUMMARY OF CROP DISTRIBUTION 1972 WATER PLAN REPORT
CROP	ACRES	DISTRIBUTION (% of Total)	DISTRIBUTION (% of Active Irrigated Acres)
Alfalfa	62,580	39.0	45.7
Native Hay	9,465	5.9	6.9
Other Hay	11,820	7.4	8.7
Pasture	41,055	25.6	30.0
Barley	2,690	1.7	2.0
Oats	7,600	4.7	5.6
Sugar Beets	415	0.3	0.3
Corn Silage	1,100	0.6	0.8
Idle	23,860	14.8	NA
TOTAL	160,585 (136, 725 active)	100.0	100.0

As shown in the table above, forage crops (alfalfa, native hay, other hay, and pasture) dominated the crop distribution for Northeastern Wyoming in the early 1970s accounting for approximately 91 percent of the total crop acreage under active irrigation (124,920 acres out 136,725 total acres). The percentage of alfalfa and grass was evenly split.

COUNTY AGRICULTURAL STATISTICS

HKM obtained crop production records from the National Agricultural Statistics Service of the USDA (http://www.nass.usda.gov/) as another source of information regarding crop distributions. This information, summarized by county, is helpful as a crosscheck against the more site-specific information developed for this project. The data was collected for the years 1970 through 1999 consistent with the study period for the hydrology task described in the "Surface Water Hydrology" memorandum (HKM, 2002). The national agricultural statistics data was verified against the data from the Wyoming Agricultural Statistics Service for the years 1998 and 1999 ( http://www.nass.usda.gov/wy/). No inconsistencies were found. The available data for 1970 . 1999 was used to calculate the average harvested acres and percentages of irrigated crops for the counties encompassed by the planning area. This information is summarized in Table 2.

TABLE 2 SUMMARY OF CROP DISTRIBUTION 1970-1999 AGRICULTURAL STATISTICS
COUNTY	ALFALFA		GRASS HAY		GRAIN		CORN		TOTAL
	Acres	%	Acres	%	Acres	%	Acres	%	Acres	%
Sheridan	28,587	66	9,143	21	4,033	9	1,592	4	43,355	100
Johnson	23,850	75	5,389	17	2,340	7	200	1	31,780	100
Natrona	16,165	57	9,185	33	1,800	6	1,104	4	28,254	100
Campbell	2,093	51	1,583	38	328	8	127	3	4,130	100
TOTAL	70,695	66	25,300	23	8,501	8	3,023	3	107,519	100

Similar to the results of the 1972 water plan, forage crops (alfalfa and grass hay) were still the dominant crops in the basin from 1970 through 1999, accounting for approximately 89 percent of the total crop acreage. However, in contrast to the 1972 water plan, the distribution between alfalfa and grass crops is now more heavily weighted towards alfalfa (65.8 percent vs. 23.5 percent).

AERIAL PHOTOGRAPHY INTERPRETATIONS

HKM obtained 1994/1996 National Aerial Photography Program (NAPP) black and white imagery as the primary basis for the mapping of irrigated lands. A total of approximately 1,150 images were acquired for the planning area. Mapping was performed by viewing the imagery 3-dimensionally, using a Lietz MS-27 three power track stereoscope.

In addition to mapping the irrigated lands and irrigation systems, HKM also utilized the stereo aerial photography as a primary basis for determining the types of crop grown in the various portions of the planning area. Consistent with the 1972 water plan and the agricultural statistics, the two primary crops grown in the basin are still alfalfa and grass (grass hay or pasture grass). HKM's certified photogrammetrist, made a visual assessment of the condition of the fields as well as the foliage density as a primary means of distinguishing between alfalfa and grass hay or pasture. Row crops such as grain crops or corn were more easily distinguished visually although they are of much more limited extent.

Each parcel of irrigated land ("polygon") in the planning area was assigned a primary crop based on the visual assessment (either alfalfa or grass). Grain and corn crops were typically found within polygons where alfalfa was the dominant crop. Because these crops constitute a relatively small portion of the total irrigated acreage in the planning area, they were represented, as a generalized percentage of the polygons where alfalfa was the primary crop. Based on a review of the agricultural statistics together with field inspections, a generalized distribution of 5% corn, 12% grains, and 83% alfalfa was used for these polygons. With this information, each of the 1200 service areas within the planning area was assigned a crop distribution attribute (% grass, % alfalfa, % grain, and % corn) in the Service Area GIS data theme ("PTServ_dd27.shp"). Service Areas are defined here as groupings of lands served by common supply ditches (with a common point of diversion).

FIELD VERIFICATIONS

A field reconnaissance was made in the Tongue River and Powder River basins during the course of the mapping work to verify the crop types being grown. Only minor modifications to the crop types were found to be necessary.

HKM also toured the basin in the company of Wyoming State Engineer Office Hydrographer/ Commissioners to determine, among other things, the types of crops grown in the various basins of the planning area. Where SEO personnel were unable to provide the necessary information, area landowners were relied upon to obtain this information. The results of this work effort are summarized in the "Irrigation Diversion Operation and Description" memorandum (HKM, 2002).

SUMMARY OF RESULTS

The resulting distribution of irrigated crops is summarized in Table 3 by HUC4 subbasin.

TABLE 3 SUMMARY OF IRRIGATED CROPS (ACRES)
SUBBASIN NAME	HUC	ACREAGE						TOTAL ACTIVE	% OF ACTIVE IRRIGATED ACRES
		ALFALFA	GRASS	GRAIN	CORN	IDLE	TOTAL		ALFALFA	GRASS	GRAIN	CORN
Little Bighorn	10080016	591	1,030	86	38	632	2,377	1,745	34	59	5	2
Upper Tongue	10090101	45,981	15,050	6,596	2,812	2,782	73,221	70,439	65	21	10	4
Middle Fork Powder	10090201	6,345	3,479	916	383	512	11,635	11,123	57	31	8	4
South Fork Powder	10090203	1,289	550	186	78	383	2,486	2,103	61	26	9	4
Upper Powder	10090202	5,821	5,239	837	353	619	12,869	12,250	47	43	7	3
Crazy Woman Creek	10090205	8,337	3,512	1,192	521	843	14,405	13,562	61	26	9	4
Clear Creek	10090206	24,223	8,464	3,490	1,471	2,063	39,711	37,648	64	23	9	4
Middle Powder	10090207	155	2,430	21	11	275	2,892	2,617	6	93	1	0
Little Powder	10090208	342	9,471	60	0	172	10,045	9,873	3	96	1	0
TOTAL		93,084	49,225	13,384	5,667	8,281	169,641	161,360	58	30	8	4

The crop acreage summarized here is used as the basis for determining irrigation water consumption in the planning area. The results are shown graphically on Figure 1.

Figure 1
Acreage of Irrigated Land By Crop

REFERENCES

HKM Engineering Inc.. Agricultural Water Use, Technical Memorandum, Powder/Tongue River Basin Plan, February 2002. Billings, Montana

HKM Engineering Inc. Irrigation Diversion Operation and Description, Technical Memorandum, Powder/ Tongue River Basin Plan, February 2002. Billings, Montana

HKM Engineering Inc. Irrigated Lands Mapping and Water Rights Data, Technical Memorandum, Powder/Tongue River Basin Plan, February 2002. Billings, Montana

HKM Engineering Inc. Surface Water Hydrology, Technical Memorandum, Powder/Tongue River Basin Plan, February 2002. Billings, Montana

Wyoming State Engineer's Office, Wyoming Water Planning Program, Report 10, Water & Related Land Resources of Northeastern Wyoming, April 1972. Cheyenne, Wyoming