Physical and Biological Characteristics
The Cottonwood Creek subbasin, 5th field hydrologic unit code (HUC) # 1706030513 drains approximately 124,439 acres in Idaho County Idaho. Cottonwood Creek is a fourth order tributary to the South Fork Clearwater River. It originates in the steep, forested lands of Cottonwood Butte and flows eastward across the rolling cropland of the Camas Prairie and into the deep canyons found in the eastern portion of the watershed, where it then enters the South Fork Clearwater River near Stites, Idaho. Cottonwood Creek flows from an elevation of 5,730 feet to an elevation of 1,332 feet. Land uses consist of cropland (74%), pastureland (7%), rangeland (13%), forestland (6%), and urban areas . The City of Cottonwood and a small portion of the City of Grangeville are found within the watershed. There are five major tributaries of Cottonwood Creek: Stockney Creek, Shebang Creek, Red Rock Creek, Long Haul Creek and South Fork Cottonwood Creek. Cottonwood Creek and its five tributaries are all listed in the Integrated §303(d)/ §305(b) Report as water quality limited from their headwaters to their mouths. Red Rock Creek is located on the Nez Perce Indian Reservation and is currently being monitored on a quarterly basis by the Nez Perce Tribe, along with 2 sites on the mainstem of Cottonwood Creek. Waterfalls that have been identified as fish barriers are found on Cottonwood Creek and Red Rock Creek at 3.6 miles and nine miles, respectively.
Climate in the Cottonwood Creek basin is characterized by cool, moist winters and warm dry summers. Air temperatures in the basin typically decrease as elevation increases. Average annual precipitation ranges from 20-25 inches across most of the basin with over 30 inches falling in the Cottonwood Butte area Monthly precipitation averages are greatest from March to June and the least during July, ranging from 2-3 inches a month in the spring to 1-2 inches per month during the rest of the year. Total precipitation in 2001 and 2005, the two IASCD sampling periods, were very similar, coming in at 19.95 and 19.42 inches, respectively. Parts of the Cottonwood Creek basin are intermittently covered with snowpack from November – March.Average annual snowfall ranges from 22 inches per year in Kooskia to 60 inches per year across the Camas Prairie. Rain accompanied by warm Chinook winds is a common occurrence in the winter and early spring and often results in high intensity runoff events. These high flow events account for the majority of Cottonwood Creek’s streamflow. During the winter, an intermittent snowpack may cover parts of the basin from November – March, providing additional runoff during rain events.