OVERVIEW

This quarterly report discusses tasks undertaken and progress made on the USU REMAP project during the period April 1 to June 30, 2000. The primary task on the project during this period was preparation for and collection of Phase II field data. Within this report, we discuss this field data collection effort.

This report is organized into the following subsections:

Phase II watersheds

Overview of field data collection during this quarter

Improved GPS

PHASE II WATERSHEDS

In the previous quarterly report, we discussed the initial selection of watersheds for analysis during this summer's field season. After further investigation, a total of five watersheds were identified for Phase II analysis. These watersheds are:

Lucky Hills Watershed, Arizona (ARS Walnut Gulch Experimental Watershed)

Kendall Watershed, Arizona (ARS Walnut Gulch Experimental Watershed)

Summit Watershed, Idaho (ARS Reynolds Creek Experimental Watershed)

Lower Sheep Watershed, Idaho (ARS Reynolds Creek Experimental Watershed)

Dugout Creek Tributary, Wyoming

These watersheds were selected because a substantial base of information is available for them and they represent a broad cross section of rangeland environments in the western US (Figure 1). Four of the watersheds are contained within the two USDA Agricultural Research Service long-term rangeland monitoring watersheds located in the western United States (Slaughter and Richardson, 2000); the fifth watershed has been the subject of several US Geological Survey investigations. Streamflow and sediment load monitoring have been conducted in all five watersheds.
 

Figure 1.  Location of Phase II watersheds being investigated during year 2000.

The Lucky Hills and Kendall watersheds are contained within the 150-km² Walnut Gulch watershed in southeastern Arizona. Semiarid grasslands and shrublands characterize the watershed, which was established as a USDA experimental watershed in 1953. Much of the approximately 375 mm of annual precipitation comes during intense, late summer thunderstorms producing flood runoff. Grasses are warm-season perennials, and predominant shrubs include mesquite and whitethorn accacia. Lucky Hills (0.76 km²) is shrub dominated whereas Kendall (0.58 km²) is grass dominated. Complete meteorological stations are located in each of these watersheds. Stream discharge and sediment loads are monitored in three subwatersheds at Lucky Hills. Flow and sediment loads are monitored at the outlet and at two subwatersheds in Kendall. In addition, sedimentation is measured in a stock pond at the outlet of the Kendall watershed. There are several experimental erosion plots in each watershed, along with various other environmental monitoring equipment. More information regarding Walnut Gulch watershed can be obtained from the ARS Southwest Watershed Research Center at: http://www.tucson.ars.ag.gov/gis/wg.html.

Two of the watersheds, Summit and Lower Sheep, are located within the 234-km² Reynolds Creek watershed in southwestern Idaho, a USDA experimental watershed since 1960. Unlike Walnut Gulch, the cooler temperatures in Reynolds Creek create seasonal snowfall precipitation and runoff due to snowmelt on frozen soil. Vegetation cover consists of cool season grasses and several types of sagebrush (Artemisia spp.). The Lower Sheep watershed (0.13 km²) is characteristic of the "smooth" topography, sagebrush cover, and frozen-ground runoff characteristic of the upper part of the Reynolds Creek watershed. Summit watershed (0.83 km²) has a more rugged topography, is characterized by shallow bedrock, and has runoff resulting primarily from rainstorm events. Lower Sheep has a complete, meteorological station and a streamflow station at its outlet. Summit has an active precipitation gage, but the streamflow and sediment monitoring station at the outlet has been inactivated. More information regarding Reynolds Creek experimental watershed can be found at:
http://ars-boi.ars.pn.usbr.gov/Reynolds/index.html

Dugout Creek Tributary watershed, a 2.1 km² watershed, is situated in a grassland prairie in the western part of the Great Plains physiographic province in northeastern Wyoming. Although cool season grasses and sagebrush are the predominant vegetation cover in the watershed, more important is the high percentage of bare ground due to the watershed's unusual geology and soils. The Cody Shale, an impermeable, fine-grained, marine shale of Cretaceous Age, underlies the watershed. The thin soils derived from the shale allow little infiltration; therefore much storm rainfall runs off rather than infiltrates. The fairly short distances required to generate overland flow have resulted in an extremely high drainage density of the watershed's drainage network. A now discontinued US Geological Survey gauging station (No. 06313180) monitored peak flows from 1965 to 1974 and continuously monitored discharge from 1974 to 1983. Sediment load data were collected during the early 1980's as part of a USGS investigation of the watershed. Several USGS investigations provide detailed information regarding the watershed (Rankl, 1982; Rankl, 1987; Rankl, 1990).
 

OVERVIEW OF FIELD DATA COLLECTION

The field season began on May 15 with a team of six undertaking data collection. We started the data collection program at the two watersheds in Arizona in order to beat the heat and the July-August monsoon season. With the exception of one short afternoon shower, we beat the rain; however, afternoon temperatures hovered around 100º F. The area had received essentially no precipitation since the previous September, so the landscape was generally yellow-brown with the exceptions of the mesquite trees and cactus (Figure 2). Fieldwork in Arizona was completed in mid June.
 

Figure 2.  Images of the Kendall watershed, Arizona from May 2000.  Top:  Looking down the watershed.  Trees are mesquite.  Bottom:  Site 37.  Note the sparse vegetation and gravel cover that characterizes this watershed.

During late June and early July, field work was conducted in the Dugout Creek Tributary watershed in Wyoming. Northeast Wyoming was actually one part of the West that received rain this year and was not on fire this summer. In fact, a light rain occurred the day before our first field day. Although many of the cool season species were beginning to brown up for the summer, the watershed still maintained a green cast (Figure 3). Fieldwork in the watershed was completed on July 5^th.
 

Figure 3.  Images of the Dugout Creek Tributary watershed, Wyoming from June 2000.  Note the greener vegetation than in the Kendall watershed above.  Top:  Looking up into the watershed.  Former gauging station is located about 30 m downstream of the bridge in the photo.  Bottom:  Sagebrush and cool-season grasses are dominant vegetation types.

IMPROVED GPS

Implementation of the protocol requires utilization of a geographic information system (GIS) for data management and data analysis (see the quarter 2 report). To enable GIS usage, all data collection locations are assigned a Universal Transverse Mercator (UTM) coordinate (northing and easting) to identify their positions on the earth's surface. Sample points are located in the field using GIS printed air photo images (digital orthophoto quarter quads or DOQQs) displaying sample point locations. Additionally, a table of sample point UTM coordinates can be printed and a global position system (GPS) unit used to find sample point location in the field.

On May 2, 2000, GPS made a major improvement when the intentional signal degradation termed SA (selective availability) was turned off. By executive order of President Clinton, SA was removed thereby increasing GPS location accuracy from about 100 meters to less than 10 meters. In fact, under some conditions, accuracy of being within a few meters of a specified location is possible. More information regarding the improvement in GPS due to the elimination of SA is available in Divis (2000).

We certainly noted the improvement in GPS as soon as we began fieldwork in Arizona. Because we are working in rangelands with little topography and a clear view of the sky, 9 or 10 satellites are usually available for the GPS unit to use in determining location. Thus, we found a high degree of correspondence between the field GPS positions and the sample point locations on the DOQQs. Figure 4 illustrates a GPS-located upland vegetation sample point and its location on a DOQQ. With the removal of SA and a combination of relatively inexpensive GPS units and high resolution DOQQs, it appears that very accurate location and relocation of monitoring points is now possible.
 

Figure 4.  Example of locating a monitoring site using a DOQQ and GPS.  Top:  DOQQ with randomly selected upland sample point (red dot) from which the vegetation transect extends.  Note that the transect cuts thorough a mesquite tree.  Bottom:  Site located using GPS coordinate derived from the DOQQ image.  Note the location of the mesquite tree that is shown on the DOQQ.

REFERENCES

Divis, D. A. 2000. SA No More: GPS Accuracy Increases 10 Fold. Geospatial Solutions, July 2000. Article available online at: http://www.geospatial-online.com/0600/0600divis.html.

Rankl, J. G. 1982. An Empirical Method for Determining Average Soil Infiltration Rates and Runoff, Powder River Structural Basin, Wyoming. US Geological Survey Water-Resources Investigation 81-76, 38 p.

Rankl, J. G. 1987. Analysis of Sediment Production from To Small Semiarid Basins in Wyoming. US Geological Survey Water-Resources Investigation 85-4314, 27 p.

Rankl, J. G. 1990. A Point-Infiltration Model for Estimating Runoff from Rainfall on Small Basins in Semiarid Areas of Wyoming. US Geological Survey Water-Supply Paper 2366, 29 p.

Slaughter, C. W., and Richardson, C. W. 2000. Long-Term Watershed Research in USDA-Agricultural Research Service. Water Resources Impact, vol. 2, no. 4, p. 28-31. Article available online at: http://www.awra.org/impact/julyimpact2.pdf.

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