This paper develops a rainfall-runoff model for estimating surface and peak flow rates from precipitation storm events on the Black Creek watershed in the Navajo Nation. The Black Creek watershed lies in the southern part of the Navajo Nation between the Defiance Plateau on the west and the Chuska Mountains on the east. The area is in the semiarid part of the Colorado Plateau on which there is about 10 inches of precipitation a year. We have two main purposes for embarking on the study. One is to determine the amount of runoff and peak flow rate generated from rainfall storm events falling on the 655 square mile watershed and the second is to provide the Navajo Nation with a method for estimating water yield and peak flow in the absence of adequate data. Two models, Watershed Modeling System (WMS) and the Hydrologic Engineering Center (HEC) Hydrological Modeling System (HMS) that have Geographic Information System (GIS) capabilities are used to generate stream hydrographs. The latter show peak flow rates and total amounts of stream flows produced from rainfall storm events. Two 24-hour rainfall amounts, 1.1 inches and 0.6 inches, are imputed into the WMS and HEC HMS modeling system and evaluated to produce 1770 cfs and 3.9 cfs of peak flows and 1106.5 acre feet and 2.7 acre feet of total flow volumes, respectively. Even though the first one seems to be a little high compared to historical peak flows from the watershed, the outcomes seem to be quite appropriate for the study area when compared with gauging site flows at other times as well as with flows from well-instrumented nearby watersheds.

The Sierra Ancha International Cooperative Program on Assessment and Monitoring of Air Pollution Effects on Forests study site or (SAEF-ICP II) is part of an international network of cooperative forest monitoring sites spread throughout Europe and the United States. The United Nations Economic Commission for Europe established the ICP II network in 1985 to monitor long-term effects of transboundary air pollution. The Sierra Ancha Experimental Forest was chosen to be a part the U.S.’s network because it is the southernmost Experimental Forest in the contiguous U.S., and because it is downwind from a major metropolitan area, Phoenix, Arizona. The site monitoring includes forest overstory growth, crown condition, foliar chemistry, understory vegetation, litterfall, soil chemistry meteorology, ozone, and deposition. This paper provides an overview of the ICP forest network, and discusses the research currently underway at the Sierra Ancha ICP II site. An overview of the challenges encountered while implementing ICP Level II monitoring will also be included.