About the Forest
About the Forest
Andrews Watershed 2 - WS02
Andrews Experimental Forest (HJA)
Watershed above the Watershed 2 gaging station
Bounding Coordinates (decimal degrees):
Slope (%): 53.19
Aspect (degrees): 318
Undisturbed control. Watershed 2 serves as the control for both WS#1 and WS#3. GIS estimated percent harvest: 2.1%
Loam and clay loam soils derived from colluvium from reddish breccias and tuffs occur in ridgetop and steep slope positions in Watersheds 1, 2, and 3. Stone content ranges from 35 to 50%, generally increasing on south-facing slopes. Depth to weathered parent material is usually over 1 m. Soils derived from greenish breccias and tuffs are widely distributed. The surface and subsurface horizons are loam to clay loam with up to 50% gravel content by volume. Depth to parent material is 0.6 m to 1.2 m. Soils derived from deep deposits of andesite colluvium occupy most of the upper portions of Watersheds 2 and 3. The surface horizon is loam to sandy loam with substantial amounts of shotty concretions and andesite stones. Subsurface horizons are massive stony loams, silt loams, or clay loams containing 25 to 80% gravel. Most soil types in Watersheds 1, 2, and 3 have moderately high field capacities (approximately 20 cm H2O for the surface 1.2 m of soil) and rapid rates of saturated moisture movement. Percolation rates are typically greater than 12 cm/hr due to the large amount and size distribution of pore spaces and stone content (Rothacher et al 1967). Stone content is the dominant factor causing variation in soil moisture storage capacity. Source: Dyrness, C. T. 1969. Hydrologic properties of soils in three small watersheds in the western Cascades of Oregon. U. S. Department of Agriculture Forest Service Research Note PNW-111. Portland, Oregon: Pacific Northwest Forest and Range Experiment Station. pp 17.
The H. J. Andrews Experimental Forest is underlain exclusively by bedrock of volcanic origin. Three geologic formations have been mapped for the HJA and correspond roughly with elevation (Swanson and James 1975). Little Butte Formation bedrock (< approximately 760 m elevation), dated as Oligocene to lower Miocene, consists of massive tuffs and breccias derived from mudflows and pyroclastic flows. Sardine Formation bedrock (760 m to 1200 m), dated as middle to late Micocene, consists of two units: a lower unit containing welded and non-welded ash flows (notably less altered than underlying Little Butte rocks of similar lithology), and an upper unit containing basalt and andesite lava flows. Andesitic and basaltic lava flows (>1200 m), termed "Pliocascade" Formation, were deposited during the Pliocene and overlie Sardine Formation material. Watersheds 1, 2, and 3 span the Little Butte-Sardine contact. Geology of these watersheds is roughly stratified by elevation. Bedrock of lower elevation areas of all three watersheds is dominated by reddish and buff-colored tuffs and breccias. At the mouth of Watershed 3, these rock types are buried under many feet of mixed colluvium exhibiting evidence of several periods of deposition. Sardine greenish tuffs and breccias dominate middle elevation bedrock in all three watersheds and extend to the ridge of Watershed 1. Associated with these rocks are numerous outcroppings of mainly basaltic flow rocks. In Watersheds 2 and 3, large portions of this bedrock are covered with a mantle (£ 20 m) of andesitic colluvium. Upper elevations in Watersheds 2 and 3 are underlain by deposits of Sardine andestic flow rock. In Watershed 1, this formation is limited to the extreme northeast corner. Most bedrock of this type is relatively unweathered with many rugged escarpments and outcroppings. Source: Swanson, F. and M. James. 1975. Geology and Geomorphology of the H. J. Andrews Experimental Forest, Western Cascades, Oregon. USDA Forest Service Research Paper. PNW-188. 14pp.
Gauged watershed area: 60.3 ha (original surveyed value used in rating equation calculations)
Watershed 2 is completely forested. Watershed 2 vegetation is typical of the western hemlock (Tsuga heterophylla) zone with an overstory of Douglas-fir and western hemlock. In a 1970 survey of Watershed 2 (Hawk and Dyrness 1975), approximately 67 percent of overstory trees were in the 450-year age class, with the remainder younger than 125 years. Understory species include rhododendron (Rhododendron macrophyllum), vine maple (Acer circinatum), sword-fern (Polystichum munitum), and Oregon grape (Berberis nervosa).
Typically, snow begins falling in November with peak snow water equivalent storage estimated to occur in Feb-April. Mean annual maximum is about 375 mm water equiv. at highest elevation. Transient snow zone with 25% precip falling as snow at lowest elevations.