Field Characterization of the Hydraulics of Steep Channels

目前还没有经过充分检验的、一贯准确的公式来计算陡峭河道（坡度为0.002）的阻力系数。总阻力的估算和流量的间接估算由于陡峭的坡度、差分选的河床、粗颗粒、局部流动转变和阶段依赖的阻力形式而变得复杂。在估计陡坡河道的粗糙度系数和流量时存在许多不确定性，这表明需要一个系统设计的程序来收集不同类型陡坡河道在一定流量范围内的数据。拟议研究的主要目标是直接测量(i)影响水力粗糙度的渠道边界配置，以及（ii）在一系列排放期间各种陡峭渠道类型的速度，水力半径和水面坡度的水力变量。我们将重点关注高梯度通道的最陡子集，它们具有级联，阶梯池或平面通道形态。次要研究目标是(i)使用Darcy-Weisbach方程计算达到规模的总阻力，以检验通道类型之间的一致性差异，并评估总阻力随阶段变化的变化率，作为通道类型的函数；（ii）评估不同阻力成分的幅度和可变性，作为通道类型的函数。（iii）测试使用R和S的平均值以外的参数更准确地评估达标总阻力的可能性，以及（iv）使用压力传感器和数据记录器开发流量的震级-频率-持续时间记录，这些记录可用于评估参数，例如与现场水文气候状况相关的水流功率的时间分布。我们将使用来自30个研究河段（每种河段10个）的90组现场数据，这些河段的长度是平均河段宽度的几倍。油田将位于科罗拉多州的East St. Louis Creek和North St. Vrain Creek沿线，以及俄勒冈州的Lookout Creek流域。东圣路易斯溪和北圣Vrain溪是融雪为主的溪流，而了望溪的中下游则是冬季雨雪洪水，产生了闪光的水线。现场数据分析将侧重于检验假设，并使用线性回归和多元回归技术来探索控制变量（w, h, R/D84， S，其他粒度测量如D84或D90）与f和fg的响应变量之间的关系。我们还将采用量纲分析，其中f取决于无量纲组，包括R/D和w/ksbank的替代测量，以及水面坡度、ksbed/ksbank、床料分选、雷诺数、弗劳德数、水流阻塞和每个通道面积的木材阻力。竞争回归模型的稳健性将使用Mallow的Cp、AIC、交叉验证技术和基于过程的解释进行评估。地球科学家、河流生物学家、土地和资源管理机构越来越多地试图估计与涵洞和桥梁设计、鱼类通道和河流稳定或恢复措施有关的陡峭河道的流量、泥沙产量和河道稳定性。间接估算流动阻力、流速和/或流量的能力对于理解和管理陡坡通道至关重要。研究结果对水资源管理、工程和生境管理等领域具有重要的参考价值。

There is presently no well-tested, consistently accurate equation for calculating the resistance coefficients of steep channels (gradient 0.002). The estimation of total resistance and the indirect estimation of discharge are complicated by steep gradients, poorly-sorted beds, coarse particles, localized flow transitions, and stage-dependent forms of resistance. The numerous uncertainties in estimating roughness coefficient and discharge for steep channels indicate the need for a systematically-designed program of data collection from various types of steep channels during a range of discharges. The primary objectives of the proposed research are to directly measure (i) the channel boundary configuration as this influences hydraulic roughness, and (ii) the hydraulic variables of velocity, hydraulic radius, and water-surface slope in various steep channel types during a range of discharges. We will focus on the steepest subset of high-gradient channels, which have cascade, step-pool, or plane-bed channel morphology. Secondary research objectives are to (i) calculate reach-scale total resistance using the Darcy-Weisbach equation to test for consistent differences between channel types, and evaluate rate of change in total resistance with stage as a function of channel type, (ii) evaluate magnitude and variability of different resistance components as a function of channel type, (iii) test the possibility that reach-scale total resistance can be more accurately assessed using parameters other than reach-averaged values of R and S, and (iv) use pressure sensors and dataloggers to develop magnitude-frequency-duration records of flow that can be used to evaluate parameters such as the temporal distribution of stream power in relation to hydroclimatic regime at the field sites. We will use 90 sets of field data from 30 study reaches (10 in each channel type) with lengths several times the average channel width. Field sites will be located along East St. Louis Creek and North St. Vrain Creek, both in Colorado, and along the Lookout Creek drainage basin in Oregon. East St. Louis and North St. Vrain Creeks are snowmelt-dominated streams, whereas the middle and lower reaches of Lookout Creek are dominated by winter rain-on-snow floods that produce flashier hydrographs. Analyses of field data will focus on testing hypotheses, and on using linear regression and multiple regression techniques to explore relations among control variables (w, h, R/D84, S, other measures of grain size such as D84 or D90) and the response variables of f and fg. We will also employ dimensional analysis in which f depends on dimensionless groups including alternative measures of R/D and w/ksbank, as well as water-surface slope, ksbed/ksbank, sorting of bed material, Reynolds number, Froude number, flow blockage, and wood drag per channel area. The robustness of competing regression models will be assessed using Mallow's Cp, AIC, cross-validation techniques, and process-based interpretation. Earth scientists, stream biologists, and land and resource management agencies increasingly attempt to estimate flow, sediment yields, and channel stability in steep channels in relation to the design of culverts and bridges, fish passage, and stream stabilization or rehabilitation measures. The ability to indirectly estimate flow resistance, velocity and/or discharge is critical to understanding and managing steep channels. Results from this work will be of great use to the water-resources management, engineering, and habitat management communities.