The efficiency of seepage meters, long considered a fixed property associated with the meter design, is not constant in highly permeable sediments. Instead, efficiency varies substantially with seepage bag fullness, duration of bag attachment, depth of meter insertion into the sediments, and seepage velocity. Tests conducted in a seepage test tank filled with isotropic sand with a hydraulic conductivity of about 60 m/d indicate that seepage meter efficiency varies widely and decreases unpredictably when the volume of the seepage bag is greater than about 65 to 70 percent full or less than about 15 to 20 percent full. Seepage generally decreases with duration of bag attachment even when operated in the mid-range of bag fullness. Stopping flow through the seepage meter during bag attachment or removal also results in a decrease in meter efficiency. Numerical modeling indicates efficiency is inversely related to hydraulic conductivity in highly permeable sediments. An efficiency close to 1 for a meter installed in sediment with a hydraulic conductivity of 1 m/d decreases to about 60 and then 10 percent when hydraulic conductivity is increased to 10 and 100 m/d, respectively. These large efficiency reductions apply only to high-permeability settings, such as wave- or tidally washed coarse sand or gravel, or fluvial settings with an actively mobile sand or gravel bed, where low resistance to flow through the porous media allows bypass flow around the seepage cylinder to readily occur. In more typical settings, much greater resistance to bypass flow suppresses small changes in meter resistance during inflation or deflation of seepage bags.

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高渗透设置中的可变渗流计效率

渗流计的效率，长期以来被认为是与流量计设计相关的固定属性，在高渗透性沉积物中并不是恒定的。相反，效率随渗流袋的填充度、袋子附着的持续时间、仪表插入沉积物的深度和渗流速度而有很大差异。在装满水力传导率约为 60 m/d 的各向同性砂的渗流试验池中进行的测试表明，当渗流袋的容积大于 65% 至 70% 或小于大约 15% 到 20% 已满。即使在袋子填充度的中等范围内操作时，渗漏通常也会随着袋子附着的持续时间而减少。在袋子连接或移除期间停止通过渗漏计的流动也会导致流量计效率降低。数值模拟表明，在高渗透性沉积物中，效率与水力传导率成反比。对于安装在水力传导率为 1 m/d 的沉积物中的仪表，效率接近 1，当水力传导率分别增加到 10 和 100 m/d 时，效率分别下降到 60% 和 10%。这些大的效率降低仅适用于高渗透性环境，例如波浪或潮汐洗过的粗砂或砾石，或具有活跃移动的砂或砾石床的河流环境，其中流经多孔介质的阻力低，允许绕流渗缸容易发生。在更典型的设置中，更大的旁路流阻力抑制了渗流袋充气或放气过程中仪表阻力的微小变化。