Cottonwood Creek (PNRS #1160) (hydrologic unit # 17060306-069) is located in the Clearwater River hydrologic basin. The headwaters are located near Reubens, Idaho. The size of the watershed is 40,980 acres. Cottonwood Creek flows in a northwesterly direction through the Nez Perce Indian Reservation joining with the Clearwater River near Myrtle (Figure 1).
Figure 1. Cottonwood Creek Location Map
Elevations range from 850 feet at the mouth of Cottonwood Creek to 3,500 feet at the watershed headwaters. Rolling upland plateaus of non-irrigated cropland with steep canyon walls and a somewhat inaccessible canyon floor typify the topography.
Steep slopes and narrow bottomlands characterize the watershed. Generally, the north and east facing slopes are forested with various tree and shrub species, whereas the south facing slopes and the flatter plateau areas are cropland.
The Cottonwood Creek watershed encompasses approximately 40,980 acres. It is located at the Clearwater River basin. It flows northwest through the Nez Perce Indian Reservation and meets the Clearwater River near the town of Myrtle. Elevations range from 850 feet to 3,500 feet. Average annual precipitation in the watershed ranges from 18 to 25 inches.
Rolling upland plateaus of non-irrigated cropland with steep canyon walls and a somewhat inaccessible canyon floor. Land ownership consists of mostly private (87.3%), tribal (12.6%), and public (0.1%). Land use consists of non-irrigated (50.9%), rangeland (34.4%), forest (13.7%), urban (0.5%), road (0.2%), and pastureland (0.3%). Agricultural crops produced include wheat, barley, lentils, garbanzo beans, canner peas, buckwheat and bluegrass.
The Cottonwood Creek watershed contains various types of fish species. These species include Steelhead, Brook trout, Speckled Dace, Paiute Sculpin, Chiselmouth, Northern Squawfish, Redside Shiner, and Bridegelip Sucker. Of these, the Steelhead, (Oncorhynchus mykiss) is listed at threatened under the Endangered Species Act.
In 1989, the Department of Environmental Quality (DEQ) reported that non-point and point pollution sources are affecting the Cottonwood Creek watershed. The pollutants cause low summer flows, extreme changes in annual stream flow, lack of in-stream cover, lack of habitat diversity, crop damage and loss due to sedimentation, crop yield loss due to erosion, as well as a reduction in wildlife populations and of species diversity due to riparian and wetland habitat loss. Non-point pollution sources include:
- Non-irrigated agriculture
- Land development (construction activities)
- Forestland harvest activities
- Grazing activities
Point pollution sources include:
- Above and underground fuel storage tank facilities
- Septic tank systems
- Agricultural chemical facilities
- Animal feeding operation
Pollutants
- pathogens
- flow alternation
- habitat alteration
- nutrients
- sediment
- thermal modification
- dissolved oxygen
- ammonia
Ownership
Of the land within the watershed, 87% is privately owned, 13% is tribally owned, and less than 1% is federal or state ownership.
Figure 2. Cottonwood Creek Ownership
Table 1 identifies the extent of ownership, while Figure 2 illustrates ownership locations.
Table 1. Cottonwood Creek Watershed Ownership
| Ownership | Acres | Percentage (%) |
| Private | 37,146 | 87 |
| Nez Perce Tribe | 5,422 | 13 |
| Federal | 53 | <1 |
| State Lands | 27 | <1 |
| Total | 42,648 | 100 |
Climate
The Cottonwood Creek watershed has a maritime climate pattern characterized by cool moist winters and warm dry summers. This climate is typical for much of the Pacific Northwest and Columbia Basin, and results from air masses and storm systems moving inland from the Pacific Ocean. Summer high temperatures above 90° Fahrenheit (F) are common in the valleys while temperatures in the high 70s are common in the uplands. January low temperatures average 24° F in the valleys and 18° F at higher elevations.
Average annual precipitation generally increases with elevation, ranging from approximately 18 inches in the lower and central portions of the watershed to about 24 inches in the higher elevation areas. Such an elevation gradient in precipitation is also typical of the region. Climate data stations located at Nezperce, Idaho and Dworshak National Fish Hatchery (NFH) near Ahsahka, Idaho, best represent the climatic conditions in the upper and lower Cottonwood Creek watershed, respectively.
Table 2. Summary of Climatic Conditions Recorded at Nezperce, Idaho and Dworshak NFH (Natural Resources Conservation Service 2000).
| Climatic Conditions | Nezperce, Idaho1 | Dworshak NFH2 |
| Avg. Annual Temperature (°F) | 45.6 | 51.8 |
| Avg. Temperature – January (°F) | 27.7 | 31.8 |
| Avg. Temperature – July (°F) | 64.5 | 72.6 |
| Avg. Total Annual Snowfall (inches) | 51.3 | 14.0 |
| Growing Season (# days)3 | 96 | 159 |
1Period of record is 1965-1990
2Period of record is 1967-1990
3Based on 80% probability of temperatures 32°F or greater
Erosion Priority Areas
Erosion priority areas were identified by using the USDA-NRCS Soil survey and identifying those soils with a K factor greater than 0.37. The K factor is a soil erodibility factor which represents both susceptibility of soil to erosion and the rate of runoff, as measured under the standard unit plot condition. Soils high in clay have low K values, about 0.05 to 0.15, because they are resistant to detachment. Coarse textured soils, such as sandy soils, have low K values, about 0.05 to 0.2, because of low runoff even though these soils are easily detached. Medium textured soils, such as the silt loam soils, have a moderate K values, about 0.25 to 0.4, because they are moderately susceptible to detachment and they produce moderate runoff. Soils having high silt content are most erodible of all soils. They are easily detached, tend to crust, and produce high rates of runoff. Values of K for these soils tend to be greater than 0.4.
Figure 3. Cottonwood Creek K Factor Soils
The majority of soils in the Cottonwood Creek watershed are silt loams. K factors for each soil type within the watershed were obtained from the USDA-NRCS Nez Perce/Lewis Soil Survey. Soils with a K factor greater than 0.37 were geospatially selected using GIS.
Common Resource Area
A Common Resource Area (CRA) is defined as a geographical area where resource concerns, problems, or treatment needs are similar. It is considered a subdivision of an existing Major Land Resource Area (MLRA) map delineation or polygon. Landscape conditions, soil, climate, human considerations, and other natural resource information are used to determine the geographic boundaries of a CRA.
There are four CRAs within the Cottonwood Creek watershed (Figure 4.)
Figure 4. Cottonwood Creek Common Resource Areas
Common Resource Area Descriptions
43A.1 Northern Rocky Mountains ¬Grassy Potlatch Ridges
The Grassy Potlatch Ridges ecoregion is underlain by volcanics and mantled by loess and volcanic ash. Idaho fescue, bluebunch wheatgrass, bluegrass, snowberry, and, on cooler, moister sites, scattered ponderosa pine occur and contrast with the forests of the Northern Idaho Hills and the forests and savannas of the Lower Clearwater Canyons. Today, small grain farming, hay operations, and livestock grazing are extensive.
43A.3 Northern Rocky Mountains Lower Clearwater Canyons
The deep, narrow Lower Clearwater Canyons are lower, drier, warmer, and have been more developed than the Lochsa¬, Selway, and Clearwater Canyons. Savanna, Douglas¬ fir¬ ponderosa pine forest, and, in riparian areas, western red cedar, ¬western white pine, grand fir forest occur. Forests are more widespread on canyon bottoms than on slopes.
Wetlands
The USDA Soil Survey for Lewis/Nez Perce counties was used to determine the extent of hydric soils within the watershed. Approximately 1,647 acres were identified and are illustrated in figure 5.
Figure 5. Cottonwood Creek Hydric Soils
Sensitive Species
Sensitive plant and animal species found in or near the Cottonwood Creek watershed are shown in Table 2.
Table 2. Sensitive Species List
| Common Name | Scientific Name |
| Plant Species | |
| Douglas’ Clover | Trifolium douglasii |
| Purple Thick-leaved Thelypody | Thelypodium laciniatum var.
streptanthoides |
| Western Ladies Tresses | Spiranthes porrifolia |
| Wolf's Currant | Ribes wolfii |
| Simpson's Hedgehog Cactus | Pediocactus simpsonii |
| Jessica’s Aster | Aster jessicae |
| Broad-fruit Mariposa | Calochortus nitidus |
| Constance’s Bittercress | Cardamine constancei |
| Palouse Thistle | Cirsium brevifolium |
| Palouse Goldenweed | Haplopappus liatriformis |
| Hazel’s Prickly Phlox | Leptodactylon pungens ssp. Hazeliae |
| Spacious Monkleyflower | Mimulus ampliatus |
| Bank Monkeyflower | Mimulus clivicola |
| Tripterocladium leucocladulum |
| Piper’s Milkvetch | Astragalus riparius |
| Green-band Mariposa Lily | Calochortus macrocarpus var. maculosus |
| Plumed Clover | Trifolium plumosum var amplifolium |
| Gold–back Fern | Pentagramma triangularis ssp triangularis |
| Spalding’s Silene | Silene spaldingii |
| Dwarf Gray Rabbitbrush | Chrysothamnus nauseosus ssp. Nanus |
| Idaho Hawksbeard | Crepis bakeri ssp. idahoensis |
| Giant Heeleborine | Epipactis gigantea |
| Sticky Goldenweed | Haplopappus hirtus var. sonchifolius |
| Salmon-flower Desert-parsley | Lomatium salmoniflorum |
| Stalk-leaved Monkeyflower | Mimulus patulus |
| Orthotrichum hallii |
| Orthotrichum holzingeri |
| Fish Species | |
| Steelhead | Oncorhynchus mykiss |
| Chinook Salmon | Oncorhynchus tshawytscha |
| Bull Trout | Salvelinus confluentus |
| White Sturgeon | Acipenser transmontanus |
| Westslope Cutthroat Trout | Oncorhynchus clarki lewisi |
| Mammal Species | |
| Pallid Bat | Antrozous pallidus |
| Townsend’s Big-eared Bat | Corynorhinus townsendii |
| Spotted Bat | Euderma maculatum |
| Long-eared Myotis | Myotis evotis |
| Fringed Myotis | Myotis thysanodes |
| Common Name | Scientific Name |
| Long-legged Myotis | Myotis volans |
| Yuma Myotis | Myotis yumanensis |
| Lynx | Lynx Canadensis |
| Western Pipistrelle | Pipistrellus Hesperus |
| Merriam’s Shrew | Sorex merriami |
| Bird Species | |
| Black-billed Cuckoo | Coccyzus erythropthalmus |
| Bald Eagle | Haliaeetus leucocephalus |
| Mountain Quail | Oreortyx pictus |
| Great Gray Owl | Strix nebulosa |
| Flammulated Owl | Otus flammeolus |
| White-headed Woodpecker | Picoides albolarvatus |
| Peregrine Falcon | Falco peregrinus anatum |
| Northern Pygmy-owl | Glaucidium gnoma |
| Pygmy Nuthatch | Sitta pygmaea |
| Reptile & Amphibian | Species | Woodhouse’s Toad | Bufo woodhousii | | Ringneck Snake | Diadophis punctatus | | Invertebrate Species | | | Columbia Pebblesnail | Fluminicola fuscus | | Shortface Lanx | Fisherla nuttalli | | Columbia River Tiger Beetle | Cicindela columbica | | Mission Creek Oregonian | Cryptomastix magnidentata | |