DEVELOPMENT OF EROSION-CONTROL STRATIGIES FOR ARCHEOLOGICAL SITES IN GRAND CANYON THROUGH THE USE OF AN EXPERIMENTAL DRAINAGE

Hundreds of archaeological sites in Grand Canyon record prehistoric occupations, but these sites are being eroded away due to a variety of surficial processes. Conventional and highly engineered solutions are not possible in this setting as Grand Canyon National Park is managed as a wilderness. Recent research in an experimental drainage has focused on developing low-technology efforts to slow the destructive effects of gullying, including check dams and hydromulch.

The experimental drainage consists of a 1.2-by-1.8-by-5.5 m sand box. Field data collected from six archaeological sites in Grand Canyon have been used to parameterize and calibrate the experimental drainage, and include survey profiles of gullies, sediment shear strength, particle-size analysis, saturated hydraulic conductivity, and precipitation. An artificial soil crust is developed with a mixture of Portland cement and sand to simulate a biotic crust. Overland flow is produced by the use of a perforated pipe connected to an orifice plate which measures the discharge. Gullies form and propagate up-slope by changing baselevel at the downstream end of the experimental drainage.

Three types of erosion-control structures: 1) parallel brush; 2) “fluffy buttress”; and 3) rock weirs were each tested 25 different times for a total of 75 tests was well as five tests using a bonded fiber matrix (“hydromulch”) to stabilize the knickpoint and surrounding area. Three of the hydromulch tests included native seed which was allowed to germinate before testing the applications resistance to overland flow. Results indicate that the current means of erosion-control through the use of stone linings and brush check dams has limited success especially at higher discharges with little discrimination between check dam types. The use of native grass seed coupled with hydromulch showed superior results when compared to the low technology check dams and needs to be further tested in the field.