Step 3 - Current Conditions INTRODUCTION - This step describes the current occurs during summer thunderstorms. Winter range, distribution and condition of ecosystem precipitation occurs mainly as snow above 4,000 feet elements. It is organized by Issue as presented in elevation, and mainly as rain below that elevation. Step 2 and answers Key Questions identified for Fluctuation of the snow level occasionally results in each issue of this step. rain causing rapid snow melt. PRECIPITATION AQUATICS The precipitation record is characterized by two distinct climate trends (Table 3-1). These alternating periods of wet and dry conditions lasted for a few HILLSLOPE PROCESSES decades. The short duration of the record and irregular nature of climatic change preclude Key Question 1- What are the dominant forecasting of these periods. The drier periods are of hydrologic and erosional characteristics and approximately 40 inches average annual processes within these watersheds, including precipitation, the wetter are of approximately 60 impacts of the 1997 flood? inches. The Happy Camp record, along with longer records from Eureka and other stations in Landslides introduce large volumes of coarse northwestern California, indicate that the period 1870 sediment to streams during episodes of intense to 1910 was a wet time; 1911 to 1937 dry; 1938 to precipitation. This results in changes in the structure 1975 wet; 1976 to 1994 dry and 1995 to present wet. of stream channels and the quality of instream Intense precipitation of 1982-83 and 1997 are related habitat. Episodes of large amounts of sediment to strong El Niño effects. The probability of production are followed by about 10 years of rapid occurrence of rare, intense storms is higher during adjustment of channel geometry. This results in the wet periods. prolonged periods of instability of instream habitat. Erosion of roads and harvested surfaces during Table 3-1 Number of Years in Annual typical rain storms contributes to the supply of fine Precipitation Ranges Showing Climatic Trends, sediment that infiltrates into spawning gravels and 1915-1999, Happy Camp, California increases the turbidity of stream water. Precipitation, INCHES 1915-1937 1938-1975 1976-1994 1995-1999* TOTAL stream flow, landslides, rock, and soil qualities are 20-30 3 0 1 0 4 30-40 10 5 8 0 23 the important elements of slope processes and 40-50 6 6 3 0 15 sediment budgets. 50-60 3 12 4 0 19 60-70 1 7 1 4 13 70-80 0 3 0 1 4 80-90 0 4 2 0 6 Hydrology Avg. Precipitati 40.6 57.6 48.8 67.0 51.2 In the central Klamath Mountains, the coastal on In climatic influence is moderated by the mountains to Inches the west. The annual precipitation during the period Range of Observations: 23.3-88.5 40.6 inches. *Data for water year 1999 are incomplete. of record (1914 to present) at Happy Camp (immediately west of the project area) ranges from 23 to 88 inches, with average annual precipitation of The occurrence of landslides is strongly influenced about 51 inches. The precipitation record is from a by climate and weather. The scale of precipitation low-elevation measuring station. There is significant intensity associated with landslide activity ranges variability in precipitation due to topography, from hours to decades. Most of the landslide activity elevation, and proximity to the coast, however there of the last 75 years occurred with the close of the is no record to describe it. The trend of annual 1938 to 1975 wet period. Many landslides were precipitation is generally lower to the east, although reactivated by intense precipitation during 1982 and there may be portions of the analysis area, 1983. Debris slides and debris flow landslides may particularly at higher elevation, that receive more also be activated by intense summer thunderstorms. precipitation than Happy Camp. Approximately 90% Numerous landslides, some inactive since 1974, of the precipitation occurs from October through May were again active in association with the New Year's from north Pacific cyclonic storms. The remainder flood of 1996-97. Most of the active earthflow THOMPSON / SEIAD / GRIDER Ecosystem Analysis OCTOBER 1999 Step 3 - Current Conditions Page 3-1 landslides move in years of above average (51 similar to the 1964 flood. These events have been inches) annual precipitation; that is they are active documented from the study of flood deposits in the about one out of two years. There are a few Klamath River and other nearby basins. The Indian prolonged periods of little earthflow landslide Creek stream gage recorded peak flood discharge in movement, the last being from 1987 to 1994. the range of 10,000 to 20,000 CFS in 1971, 1972 (three events), 1974, 1980, and 1982. Such events STREAM FLOW are substantially more frequent during wet trends (as described in the Precipitation section above). Water quality of streams in the analysis area is very Coghlan (1984) concluded that the return probability good. Turbidity is very low, except during times of of a 1964-style precipitation event, and thus flooding, intense precipitation when surface erosion and would occur once in 45-50 years. He estimated a landslide activity is high. Damage to riparian return probability of once every 25-30 years for 1955 vegetation by 1987 wildfires was limited and has and 1997-style flood events (about 20,000 CFS peak recovered. The water quality data available includes discharge in Indian Creek) during wet trends. a 42 year record of average daily discharge for Indian Creek, a 30 year record of daily turbidity in Elk In the long-term, stream discharge, driven by Creek, and undocumented observations of turbid average annual rainfall of 51 inches, provides flow. Both Indian and Elk Creeks are located erosional power that exceeds that necessary to adjacent to and west of the analysis area, but are transport the sediment delivered to channels. roughly representative of stream conditions in the Sediment is generated and transported primarily analysis area. during peak stream-discharge events. There are two important aspects of this general behavior that are Streams in the project area are high-gradient, most relevant to the assessment of effects: 1) coarse-bedded and, due to uplift of the region, Infiltration of fine sediment (either in traction or erosion dominated. Channels typically run in steep, suspension) into spaces in the coarse framework of narrow gorges. Although influenced by large the channel bed, and 2) deposition of coarse landslides and bedrock structure and composition, sediment and included fine sediment delivered by channel patterns are dendritic. Except for broad, landslides. Fine sediment generation and transport coarse alluvial deposits in the vicinity of the mouth of events are seen a number times every year in the Seiad and Grider Creeks, relatively little sediment is Elk Creek record. Turbid storm-flow occurs about stored in stream channels. Channels are typically 5% of the time. Storm-flow turbidity typically lasts a cut in bedrock. In the Old Landslide Terrane, few hours to a few days after cessation of rainfall. channel banks are commonly of earthflow landslide The coarse fraction is less easily transported and deposits, so there is very little mechanical resistance may be temporarily stored in stream channels as of bedrock. Stream channels in the assessment bars, terraces and debris jams (Lisle 1987) and local area are similar to those described by Grant (1986) alluvial plains. Madej (1987) found the residence and Grant and others (1990) in west-central Oregon. time of coarse sediment in Redwood Creek to be on Most of the coarse sediment generated to stream the order of decades for active alluvium and channels is delivered by landsliding. Fine sediment hundreds to thousands of years for alluvium stored in is generated by surface erosion of disturbed areas, older stream terrace deposits. In a study of stream as well as landsliding. bed elevation from U.S. Geological Survey stream gages, Lisle (1981) found a decade of high rate of In Indian Creek, summer low flows are about 40 channel bed adjustment to the large input of cubic feet per second (CFS). The average flow sediment from the 1964 flood event. (exceeded 50% of the time) is about 400 CFS. Storm flow (with a return probability of once in a few One of the delivery mechanisms of coarse woody years) is about 4,000 CFS. The peak discharge debris (tree stems, roots, and branches) to stream during the flood of 1964 is estimated to be 40,000 channels is by debris flow from adjacent slopes. CFS. Roughly half of the total discharge of the Such material often accumulates as debris jams that streams occurs in close association with storms. form in first through fifth order streams. Temporary The remainder is delayed by movement through soil dams formed by landslide deposits or debris jams in and bedrock, emerging at springs. Poorly integrated channels have occurred at Murder's Bar (circa 1955), drainage networks and thick soil in Old Landslide Nordheimer Flat (1964), North Russian Creek (circa Terrane result in less efficient drainage. The steep 1974) of the Salmon River (Klamath Mountains) slopes, thin soils, and well integrated drainage of the (Juan de la Fuente, personal communication 1989) Metasedimentary Terrane result in more efficient and at Happy Camp (1964). Such dams occur on a drainage. Since flood data has been collected only variety of scales and may fail suddenly, resulting in in the last few decades, statistical analyses have a floods. high degree of uncertainty. Several floods in the past few hundred years have been of a magnitude THOMPSON / SEIAD / GRIDER Ecosystem Analysis OCTOBER 1999 Step 3 - Current Conditions Page 3-2 THE FLOOD OF NEW YEARS DAY, 1997 strongly deformed, rapidly uplifted, and deeply eroded.