The Changing Hydrologic Pattern of the Renton-Sumner Lowland, Washington

Abstract

THS CHANGING HYDROLOGIC PATTERN OF THE RENTON-SUMNER LOWLAND, WASHINGTON John O. Dart Portland State College One of the earliest regions of farm settlement in the Puget Sound Trough, the Renton-Sumner Lowland, has been an area of historic conflict in the nomenclature of its streams. This situation has developed because of several major changes in the drainage pattern, all of which have occurred in modern times within a relatively limited area. Th« lowland is a north- south trending glaciated trough approximately twenty-five miles long and two to three miles wide parallel to the sound and separated from it by a narrow strip of rolling upland. This western upland along and a similar one to the east serve as sharp physiographic boundaries. On the north the valley is terminated by the shore of Lake Washington and in the south it merges with the westward trending Puyallup Valley. This region is a pre-glacial stream channel which has been deepened and widened by the Puget Sound lobe of the Cordilleran ice sheet. As the ice retreated, lakes and streams fed by melt-water deposited a thick layer of sediments , leaving a wide, flat floor, modified in minor respects by thepost-glacial streams. The present rivers of the lowland include the Cedar, the Green, and the White. Cedar River heads in Cedar Lake on the western slopes of the Cascades , off map 1 to the east. Under natural conditions this would provide a steady flow, but the lake provides Seattle's water supply, and the volume decreases during the summer months. Reaching the valley at its northern end, the Cedar has constructed an alluvial fan which formed the original site of Renton. Fed by a number of small streams high in the Cascades near Stampede Pass, the Green River has a steep gradient and has cut a deep gorge in the hard rock formations well to the east of map 1. Below this point it flows through the folded structure of the Puget Group and the glacial drift of the plateau, reaching the lowland northeast of Auburn. With their sources at Emmons, Frying Pan, and Winthrop glaciers, the east and west forks of the White River converge on the north elopes of Mt. Rainier , while the main tributary, the Greenwater, drains the western flanks of the Cascades well off map 1. The White enters the trough east of Auburn and the town is built on the fan formed by the aggrading stream. Prior to 1906, the two major streams of the lowland, the Green and the White, entered the valley within a short distance of each other and both flowed lorthward, the Green joining the White about a mile northeast of Auburn. Durng floodtime , the White would occasionally spill a small portion of its volume nto the Stuck River, a shallow distributary which carried its waters southward nto the Puyallup River, just south oí Sumner. The flow was never long enough tor in sufficient quantity to develop a well defined channel through the low swampy iasin. At the southern extremity the floor of the lowland rises sharply, built ip by deposition from the Puyallup. During this sedimentation, however, there ras sufficient volume from the Stuck to maintain the opening into the Puyallup· After receiving the waters of the Green, the augmented White River conlnued to flow northward, meandering widely over the flat valley in a channel 5-20 feet deep between well developed natural levees. Just west of Renton 20 Yearbook of the Association VOL. 14 lAKt SEATTLE WAiHittere* TACOMA mam STREAM PATTERN BEFORE HOÉ, ..... LCAVLAND BORDER 1952 of Pacific Coast Geographers 21 LAHt STATTLE WAtHIfCTtM ENTOM D STREAM PATTERN SINCE ? 17 LOWLAND BORDER to mu* ? 22Yearbook of the AssociationVOL. 14 the river cut into the valley side and flowed through a narrow gap to Elliot Bay. At the point where the river left the lowland it was joined by the Black River, a narrow rapid stream which was the outlet for Lake Washington. Its depth varied from a few inches to several feet, regulated by the waters of the lake and the Cedar River which flowed into it from the east. As the Black entered the White, the latter became...