THE NACHES REACH By Morris L. Uebelacker, Clay P. Arango, and Douglas J. Eitemiller Located on the mainstem Naches River within the Ridge and Canyon landscape (plate II), the Naches Holocene floodplain encompasses 3,342 hectares. This floodplain is characterized by a complex interface of Columbia River Flow Basalts and Cascade volcanic material Loss Of Lateral Connectivity (Bentley 1984). Situated between two major geological units, the Ellensburg Formation intermingles with Columbia River Flow Basalts (Schmincke 1967) along its northeastern To The Naches Holocene Floodplain margins and flows of Tieton Andesite (Swanson 1978) on its southwestern boundary, the Naches Naches River has excavated material from these units to form a wide, steep-sided canyon. From 1884 To 2002 The Naches Holocene floodplain lies in stark contrast with the canyon that embodies it, which has emerged over more than ten million years of geologic time. Consequently, it is structurally set apart from all other floodplains within the Yakima Basin. Reflecting these 3500 unique geological structures and geomorphic history, the gradient of the Naches River and its Holocene Floodplain Prior to 1884 = 3,342 ha attendant floodplain is steeper than all other floodplain reaches along its longitudinal scale. As the Naches River's major tributary, the Tieton River greatly amplifies the alluvial cut and fill 3000 processes of the Naches in forming its floodplain. Both rivers enter the floodplain through confined, steep gradient canyons and deliver a powerful springtime flood pulse across the 2500 floodplain landscape. Although initially evaluated for a railroad route that would link interior and coastal 2000 economies (Stevens 1855), the canyon topography of the upper Naches drainage proved too Hectares difficult for early railroad construction. Instead, surveyors chose a route through the Yakima 1500 Canyon and upper Yakima River basin. Because the railroad was built through the Naches floodplain later than in other reaches, it was not subject to the effects of lateral confinement 1000 Loss of Loss of Loss of typical of other mainstem Yakima River floodplains. For this reason, the initial lateral Holocene Floodplain Holocene Floodplain Holocene Floodplain Surface Connectivity Surface Connectivity Surface Connectivity confinement of the Naches floodplain was ephemeral and largely conditioned by county roads Fro m 1884-1915 = Fro m 1916-1964 = Fro m 1965-2002 = 500 794 ha 1018 ha 108 ha and the old Naches Highway. Some of the earliest attempts at floodplain agriculture focused on the Naches Holocene floodplain (Buckley 1936). Irrigation diversions constructed in the late 1800s moved water from the active hydrologic floodplain to areas west of Yakima. As 0 Of the 3,342 ha of Holocene floodplain habitat settlement and land use intensified, demand for irrigation water quickly outpaced supply. The within the Naches Reach that exhibited construction of Bumping Lake Dam (1910), Clear Creek Dam (1914), and the larger Tieton surface connectivity to the mainstem Yakima River prior to 1884, a total of 1,422 ha (~43%) remain connected. Reservoir (1925) by the Bureau of Reclamation increased water supplies and permitted the expansion of irrigated agriculture. Accordingly, the flow of the Naches River was altered, as was its floodplain's hydrologic patterns and processes. The building of these federal projects required significant investments in transportation Gleed infrastructure on the Naches floodplain that included railroads, roads, bridges, and flood revetments. The town of Naches was a railroad terminus and served as a major hub for Revetments supplying the needed materials for the construction of storage reservoirs and early state Roads highways over the Cascades. The town also served the established domestic stock industry that used the high pastures of the upper Naches Basin during summer, and the emerging Alterations 1884-1915 agricultural community. Although some of these features existed before 1915, no clear Alterations 1916-1964 developmental break was evident before this date, so they are included in the 1916-1964 period for cartographic clarity. Surficially connected areas on the Holocene floodplain were Alterations 1965-2002 reduced to 2,548 hectares by 1915. Upgrading of U.S. Highway 12 to a double lane road was the major structural disconnection across the Naches Holocene floodplain during the second period of analysis. Pasture and hay farming were located adjacent to the river and dominated land use in floodplain areas more susceptible to flooding. The long-standing use of the Holocene floodplain margins as wintering grounds for sheep and cattle operations diminished throughout this period. Orchards and row corps dominated land use on the disconnected floodplain and adjacent terraces. Fruit processing facilities and saw mills marked the Anthropogenic Features industrial development of the floodplain, and the city of Naches continued to function as a central node for resource extraction activities in the upper watershed. By the close of this Responsible For The Loss Of Lateral Connectivity period, the disconnected portions of the floodplain at its lower end were being transformed Naches into a suburban landscape. By 1964, the surficially connected area of the Holocene floodplain To The Naches Holocene Floodplain within this reach had decreased to 1,530 hectares. Today, the suburban landscape continues to expand across large parts of the floodplain. Golf courses, rural residential zones, and subdivisions have begun to dominate the floodplain displacing orchards and other irrigated agricultural uses. These transformations have mostly occurred in areas of the floodplain previously precluded from surficial connection with the Naches River. During the last period of analysis, the surficially connected portion of the Naches Holocene floodplain dropped to 1,422 hectares. Today, only 43% of the Naches Roads Holocene floodplain remains surficially connected. Nevertheless, relative to the large unregulated portions of its headwater basins, the flood potential of this remaining area is significant. Results from the GIS analysis of the hydrologically active portion of the Naches Holocene floodplain show a reduction from 803 hectares in 1927 to 689 hectares today. Presently, 14% of the active floodplain habitat present in 1927 has been lost (plate XX). The difference in discharge of the mainstem Yakima River at the Naches gauging station near the city of Naches (NACW) between 1927 and 1992 aerial photography disallows a Flood Revetments comparison of all channel types and lengths for this floodplain. However, comparisons of the mainstem river length can be made (apendix I). This difference was less than 1% between the second and last period of analysis. The Naches floodplain has not experienced the magnitude of channel simplification and active floodplain confinement evident within the other reaches. Furthermore, despite the major pulse near the end of the water year due to flip-flop, the 0 5 10 15 20 25 hydrograph of the Naches River still expresses the effects of a significant spring flood pulse. Kilometers These factors may contribute to the consistency of main channel length between the last two periods. REFERENCES Flood Revetments Bentley, R. D. 1984. Western Columbia Plateau margins studies, Tieton River to Roads Gleed Yakima River. In: Preliminary Safety Analysis Report: Washington Public Power Supply System Nuclear Project. 1(2A): 2R D.6-1R D.6-34. Railroads Buckley, W. 1936. A geography of the Yakima Region. Ph.D. Dissertation, Ohio Alterations 1884-2002 State University. Schmincke, H. U. 1967. Graded lahars in the type sections of the Ellensburg Formation, south-central Washington. Journal of Sedimentary Petrology, 37: 438-448. Stevens, I. I. 1855. Narrative and Final Report of Exploration for a Route for a Pacific Railroad, near The Forty-Seventh and Forty-Ninth Parallels of North Latitude, from St. Paul to Puget Sound. Thomas H. Ford, Printer, Washington. Swanson, E. A. 1978. Geologic Map of the Tieton River Area, Washington. Geological Survey Miscellaneous Field Studies Map MF-968. N W E produced by S YAKIMA REACHES PROJECT 0 .4 .8 1.2 1.6 km Conversion Constants Cartography By Multiply Hectares by 2.47 to obtain Acres reaches CWU Position of the Naches Reach within the Yakima Basin. Multiply Kilometers by 0.621 to obtain Miles 0 1 mi Douglas J. Eitemiller C 2002 Not to be reproduced without permission Plate XIX. Loss of lateral connectivity to the Naches Holocene floodplain and the anthropogenic features responsible for that loss. Loss Of Active Floodplain Within The Naches Reach From 1927 To 2002 Active Floodplain in 1927 = 803 ha Active Floodplain in 2002 = 689 ha Naches 0 200 400 600 800 1000 Hectares Of the 3,342 ha of Holocene floodplain habitat within the Naches Reach, 803 ha were mapped as active floodplain habitat in 1927. By 2002, active floodplain habitat was reduced to 689 ha, a loss of ~14%. Gleed Active Floodplain-1942 Active Floodplain-2002 N W E S produced by YAKIMA REACHES PROJECT 0 .4 .8 1.2 1.6 km Conversion Constants Cartography By Multiply Hectares by 2.47 to obtain Acres reaches CWU Position of the Naches Reach within the Yakima Basin. Multiply Kilometers by 0.621 to obtain Miles 0 1 mi Douglas J. Eitemiller C 2002 Not to be reproduced without permission Plate XX. Loss of active floodplain within the Naches reach from 1927 to 2002..