River Recovery at Mount Pinatubo, Philippines

菲律宾皮纳图博山河流恢复

• 批准号: 0106681
• 负责人: David Montgomery
• 金额: $ 19.35万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2005-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0106681&HistoricalAwards=false
• 关键词: River; Recovery; Mount; Pinatubo; Philippines

0106681MontgomerySince the 1991 eruption of Mount Pinatubo, the sediment yields from watersheds draining its slopes have been the highest ever recorded. In spite of this overwhelming sediment load, rivers inundated by pyroclastic flow deposits efficiently delivered almost half of the initial deposits to downslope alluvial/debris fans by 1996. Much of this transport occurs by lahars and hyperconcentrated flow, but at low to moderate flow the channels provide end-member examples of channel response to high sediment supply. A program of field measurements in 1997 and 1998 documented extremely high bedload transport rates even at low flow due to enhanced mobility of particles moving over a smooth, fine-grained bed. Measurement of flow velocities and depths, channel properties, and the size of both mobile and stable clasts in the Pasig-Potrero and Sacobia Rivers indicates grain-size-independent dimensionless critical shear stresses of 0.015 to 0.038, and Manning's n values of 0.017 to 0.024, well below values previously reported for steep mountain channels. The dramatic bed mobility and selective transport in these extremely sediment-rich channels indicate that changes in grain size, and bed roughness can increase transport capacity in response to high sediment supply. Dimensionless bedload transport rates in the Pasig-Potrero River are substantially greater than those previously reported for temperate rivers at the same dimensionless shear stress. Over the course of three field seasons, we propose to test a series of hypotheses for river response to changes in sediment supply using this ongoing natural experiment. Specifically, we will monitor channel response to the progressive decline in sediment supply to evaluate the hypotheses that: (i) bed coarsening and armoring is occurring in response to decreased sediment delivery from hillslopes and valley walls and will lead to a change in the character of bedload transport from selective mobility to threshold mobility; (ii) that recovery of an armored, threshold mobility bed in the Pasig-Potrero River will occur faster than in the Sacobia River due to differences in watershed recovery and relative transport capacity; (iii) that the magnitude and rates of changes in the bed surface texture in rivers draining the flanks of Mount Pinatubo track differences in initial sediment loading of their watersheds by pyroclastic flow deposits; and (iv) that pebble cluster formation is a mechanism of channel response to declining sediment load that, in turn, leads to changes in the style of bed mobility and bedload transport rates.

0106681 Montgomerysince 1991年Pinatubo山的喷发，沉积物的产量是从流水的流域产生的，这是有史以来最高的记录。 尽管这种压倒性的沉积物负荷，但在1996年，被火山碎屑流沉积物淹没了几乎一半的初始沉积物到下坡冲积/碎屑风扇。这种运输的大部分发生在拉哈尔斯和高浓度的流量中，但在低到中等流量的情况下，频道的流量为中等流量提供了渠道供应的最终供应供应频道供应的频道响应供应。高空供应供应到高层供应。 1997年和1998年的现场测量程序也记录了由于颗粒在光滑，细粒度的床上移动的增强，即使在低流量下，也有极高的床负载运输速率。 在Pasig-Potrero和Sacobia Rivers中流动速度和深度，通道特性以及移动和稳定碎屑的大小的测量表明，无谷物大小的无尺寸无尺寸临界剪切应力为0.015至0.038，Manning的N值为0.017至0.017至0.024，以前是0.017至0.024的n值，以前报道了陡峭的山路。 在这些极端沉积物的通道中，戏剧性的床迁移率和选择性运输表明，晶粒尺寸的变化和粗糙度可以增加对高沉积物供应的运输能力。 Pasig-Potrero河中无量纲的床载运输速率大大比以前报道的温带河流在相同的无尺寸剪切应力下的床位运输速率要大得多。 在三个赛季的过程中，我们提议使用这种持续的自然实验来测试一系列假设，用于河流对沉积物供应变化的反应。 具体而言，我们将监视对沉积物供应逐渐下降的渠道响应，以评估：（i）响应于从山坡和山谷墙的沉积物递送下降，并将导致床位从选择性迁移到阈值迁移到阈值迁移的特征，以响应减少山坡和山谷墙的散布而发生的假设； （ii）由于分水岭恢复和相对运输能力的差异，帕西格 - 帕特罗河中的装甲阈值移动床的恢复速度将比萨科比河的恢复速度快； （iii）河流中床表面纹理的幅度和变化的速度和变化，这些河流的侧面质地降低了皮纳图博山脉的侧面轨道轨迹差异在其流域通过火山碎屑流沉积物在流域的初始沉积物载荷中的差异； （iv）卵石簇的形成是通道反应下降沉积物负荷下降的机制，进而导致床迁移率和床负载传输速率的变化。