Methane Sampling Technique and the Measurement of Plunge Pool Impact on GasTransfer Rates at Low-Head Hydraulic Structures

摘要

In situ dissolved methane gas was used as a tracer for estimating the gastransfer rates of flow over low-head hydraulic structures. The methane measurement provided a means to assess the effects of the plunging flow in the structure stilling basin. Simultaneous oxygen-methane transfer measurements and nitrogen-methane measurements were used to develop the concept of an effective depth, which is the mean depth to which entrained air bubbles are transported in the stilling basin. Generally, as discharge increased, the mean depth increased probably as a consequence of the increase in momentum. Effective depths computed with oxygen-methane measurements were very similar to effective depths computed with oxygen-nitrogen measurements, thus verifying the concept of effective depth. Additional measurements should be performed at other structures to relate the effective depth to parameters of the spillway jet and stilling basin. (MM).