Wagon Wheel Gap, CO (USA) 1910-1926
Location and Scale
A paired catchment experiment at Wagon Wheel Gap, Colorado, USA (N 37° 46', W 100° 53')
Catchment A 222.5 acres (90.0 ha) Catchment B 200.4 acres (81.1 ha)
1910 - 1926
A mean annual temperature of about 34° F (1° C)
A mean annual precipitation of about 21 inches (533.4 mm) about half snow and half rain. Except on the south slopes there is practically no melting throughout the winter until after March 1.
A mean evapotranspiration estimated at about 15" (381mm)
Runoff coefficients ranging from 17% in dry years to 42% (Bates and Henry, 1928)
The geological formation of the locality, a quartzlatite flow of great uniformity over the two watersheds, and the coarse, sandy soil derived therefrom, containing and covered by many small rock fragments, were conducive to a very high degree of absorption of rain and snow water. Hence there appeared very little surface run-off at any stage of the experiment, and the quantities of soil eroded were of extremely small magnitude. Catchment B was a more effective storage reservoir than Catchment A. (Bates and Henry, 1928)
Elevation range of the catchments was between 9000 and 11000 ft (2743 - 3353m). Catchment A was longer narrower and extending to higher elevations than catchment B. Average slopes were 25 per cent for Catchment A and 26 percent for catchment B. Mean aspect for A is S 85°E and for B N65°E, a difference of 27 degrees.
Vegetation / Land Use
The forest cover of both watersheds, though far lighter than the undisturbed stands at similar elevations in the Rocky Mountain region, was fairly typical of the region as a whole, it having been heavily visited by fires. The original forest was mainly Douglas fir at the lower and Engelman spruce at the higher elevations. These areas were burned over in 1885, with watershed B (the one which was denuded in the experiment) having been burned somewhat more extensively than A. The burned areas had come back largely to a scrubby growth of aspen, which, while forming dense thickets and thereby protecting the soil adequately, is obviously less effective than conifers as a shade to retard the melting of snow. (Bates and Henry, 1928)
The two catchments in the Rio Grande National Forest, close to the railway station at Wagon Wheel Gap were chosen by the US Forest Service. Both daily meteorological data and discharge data were collected from 1910. Discharges were measured using thin plate weirs, initially rectangular and from 1911 triangular 90 degree V notch weirs. Meteorological data were collected at 2 sites in each catchment, including snow depths, with Marvin pattern snow gauges added later.
Catchment B was deforested (apart from a riparian strip) starting in July 1919 and ending late in 1920. Regrowth of aspen followed, reaching a height of about 1.2m by the end of the experiment.
Bates and Henry (1928) conclude "The flood run-off of watershed B before denudation was the same 8s that of A; after denudation of B the spring flood on that watershed increased to a peak discharge in the third year after denudation of about 35 per cent excess and then diminished until the end of the experiment when it was 22 percent greater than that of A."
"During the predenudation period the average annual silt load carried to the dam by stream A was 691.5 pounds net dry weight, and that carried by B was 568.5 pounds. In the second period A carried an average amount of 477 and B 3,340.1 pounds. The ratio B/A therefore increased from 0.822 to 7.002, or was about eight and one-half times as high after denudation.
Most of the larger quantities of silt were obtained in the July cleanings of the basins, covering flood periods after April 15. The ratio of B to A for this quarter before denudation was 0.75 and after denudation 9.12. An increase of about 50 per cent in the average height of B flood crests, together with any direct effects of denudation on the soil, are seen, therefore, to have magnified the silt load of the stream twelve times."
Van Haven (1988) reports on a re-analysis of the data from Wagon Wheel Gap. Annual hydrograph parameters were generated for the two paired watersheds for the pre- and postreatment periods and tested using regression and covariance analyses. Average annual water yield, maximum daily discharge, high-flow volumes, recession flows, and baseflow were all increased significantly following complete deforestation of one watershed. With the exception of the first full year after treatment, deforestation had little effect on hydrograph timing. Deforestation increased both the slope and intercept of a linear equation describing the flow duration curve of Watershed B. These results agree with the results reported from the original study. However, some of the original study results for other hydrograph parameters could not be statistically supported.
The Wagon Wheel Gap study has been much cited in reviews and other studies of forest hydrology and paired watershed experiments.
C G Bates was Chief of Silvics for the US Forest Service Dsitrict 2 at the time of the Review of Forest Service Investigations in 1913.
A J Henry became Chief of the Division of Records and Meteorological Data of the US Weather Bureau
Van Haveren, B.P., 1988. Notes: A Reevaluation of the Wagon Wheel Gap Forest Watershed Experiment. Forest Science, 34(1), pp.208-214.
Bates, C.G. and Henry, A.J., 1928. Forest and stream flow at Wagon Wheel Gap, Colorado. Final report'. Mon. Weath. Rev. Suppl, 30, pp.1-79.
Bates, C.G. and Henry, A.J., 1928. Second Phase of Streamflow Experiment at Wagon Wheel Gap, Colo. Monthly Weather Review, 56(3), pp.79-80.
Bates, C G and Henry A J, 1921, Streamflow at Wagon Wheel Gap, Colo., Monthly Weather Review, 49(12), 637-650
Bates, C.G., 1921. First results in the streamflow experiment, Wagon Wheel Gap, Colorado. Journal of Forestry, 19(4), pp.402-408.
Frankenfeld, H C, 1910, The experimental station at Wagon Wheel Gap, Colorado, Monthly Weather Review, 38: 1453-1455