Self-Stabilizing Tendencies of Alluvial Channels
01 May 1970-Journal of the Waterways, Harbors and Coastal Engineering Division (ASCE)-Vol. 96, Iss: 2, pp 235-249
TL;DR: In this paper, the authors proposed a design criterion for stable channels constructed in coarse non-uniform alluvial material, which integrates the stabilizing influence of all grain sizes present in a self-stabilized armor coat and permits operating the channel at a preset factor of safety.
Abstract: Channels constructed in coarse alluvial material tend to develop an armor coat at the bed's surface protecting the material beneath the top layer from further erosion. A method is outlined which permit the prediction of the eroded material. Based on these results, it is possible to make an estimate on the minimum amount of material to be eroded prior to development of a stable condition resulting from amoring. An attempt is made to determine those condition which result in a finally stable bed. This leads to a design criterion for stable channels constructed in coarse nonuniform alluvial material. This design criterion integrates the stabilizing influence of all grain sizes present in a self-stabilized armor coat and permits operating the channel at a preset factor of safety.
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TL;DR: In this article, the authors analyzed how hydrologic regimes vary with land use in four large watersheds that span a gradient of natural land cover and precipitation across the continental United States.
392 citations
Cites background from "Self-Stabilizing Tendencies of Allu..."
...Bed coarsening, armoring, and increased bed stability may result from increased durations as finer material is winnowed from gravel-cobble beds (Gessler, 1970; Parker and Sutherland, 1990; Reid and Laronne, 1995; Almedeij and Diplas, 2005)....
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TL;DR: Stable reticulate structures have been observed in cobble-gravel channel beds with low bed material transport rates as mentioned in this paper, showing that such structures develop simultaneously with the armor layer during an extended period when flows do not exceed the Shields threshold.
Abstract: Stable reticulate structures, which we call “stone cells,” have been observed in cobble-gravel channel beds with low bed material transport rates. Experiments show that such structures develop simultaneously with the armor layer during an extended period when flows do not exceed the Shields threshold by more than ∼2 times, so that bed material transport is low. They are constructed by particles moving from less stable positions into more stable configurations against each other. Intermediate developments include clusters and stone lines. They reduce sediment transport by orders of magnitude and are evidently a major stability-promoting mechanism in gravel channels. The timescale for their development suggests that the boundaries of many gravel-bed channels are not in equilibrium with recent competent flows but reflect the history of recent “dominant” flows.
338 citations
20 Nov 1971
TL;DR: In this paper, Gessler et al. describe the degradation process of an armoring coat and show that it is a degradation process that occurs when the garment is worn by a person wearing it.
Abstract: 混合砂礫河床 において は, 河床砂礫 が流水 による分級 作用 を うけてその粒 度構成 に変化 をきたすが, それ に応 じて限界掃流 力や流 砂量が変化す るので均 一砂礫河床 と は異な った変動特性 を示す場 合が ある。ダ ム築造後下流 の河床砂礫 の粒 度が次第に粗 くなる armoring 現象 はそ の典型的 な例 であ る。 したが って, 将来 の河床変動 を予 知す るた めには, 同時に将来の河床砂礫 の粒 度分布 を予 測す ることが必要 であ り, この問題 は河川 工学 にお ける 重 要な研究課題 の一 つであ ると考 え られ る。 ダ ム下流 の armoring 現 象につい ては以前 か ら注 目さ れ てお り, 現地河川 におけ る実測や水路実験 に よる研究 が な さ れ て き た。た とえば, Garde お よび Hasan 1) (1967) は水路実験 と San Louis canals の資料 か ら最終 状態 にお ける armor coat の代表粒径 を初期河床 材料の 標 準偏 差 (√d84/d16) か ら求 め る経 験的 な方法 を提 案 し てい る。また, ダム下流 の河床 低下計算 に armoring の 効果 を導入 す る 最初 の試み は, 河 村 お よ び Simons 2) (1967) に よりな され ている。 しか し, これ らの研 究 に おいては粒 度分布 につ いての考 察はな され ていない。最 近, Gessler3) (1970) は河床低 下 を河床が ほぼ平行 に 低 下 して掃流 力が 時 間的に 変化 しな い parallel degradation と河床勾 配が変化 して掃流力 が 次 第 に 減 少 す る rotational degradation の 2 つの形 態に分 け, 前 者の領
288 citations
TL;DR: In this article, a 2D analysis of fluvial process related to flow with vegetation is introduced with typical processes, which concerns with changes of river landscape and changes in river landscape.
Abstract: Recently, vegetation is a key of river management where environmental aspects should be taken care of as well as the safety against flood and the water resources utilization Then, the management of fluvial processes related to vegetation is inevitably important, and fluvial hydraulics and hydraulics of flow with vegetation must support it These two fields have been recently developed obviously, and coupling them must provide us answers to various emerging problems in new river engineering In this paper, after an explanation how to treat the flow with vegetation, 2D analysis of fluvial process related to flow with vegetation are introduced with typical processes Particular interests are paid on the topics of fluvial process related to flow with vegetation which concerns with changes of river landscape
216 citations
TL;DR: In this paper, the authors show that pavement can coexist with the motion of all available grain sizes because motion is sporadic, so that at any given time only a small percentage of surface grains are actually in motion.
Abstract: Laboratory experiments which model streams with poorly sorted gravel beds at reduced scale reveal that pavement is a mobile bed phenomenon. It acts to decrease the inherent difference in mobility between large and small grains by overrepresenting the percentage of large grains exposed to the flow. Pavement can coexist with the motion of all available grain sizes because motion is sporadic, so that at any given time only a small percentage of surface grains are actually in motion. Particles in the immediate subpavement are only occasionally moved, and deeper particles are hardly ever moved. The experiments were conducted at constant discharges. They provide accurate quantitative models of two field streams in that they obey the same bedload law as field data. Both sediment feed and recirculating configurations were utilized. The only systematic difference between the two is in the behavior of the finer grains.
177 citations