FLOW STRUCTURES DETERMINING RIVER LEVEL IN AN ESTUARY

为了掌握洪水期间的流量以及农业和水力发电等河水的利用情况，必须找到流量与河水水位之间的正确关系。通常情况下，河流流量是通过经验H-Q方程由水位给出的，其中H是水位(高度)，Q是流量，但在干旱期间，将该表达式应用于河口比应用于上游变得非常困难。这是因为在潮汐、大气压力、风向和风速四个关键因素的影响下，河流水位可以取很大范围的值。本文试图推导出一种定量估计潮汐、气压、风向和风速对石卡里河河口流量影响的方法，其中这四个因素显著降低了水位(H)和河流量(Q)之间的相关性。研究发现，潮汐和大气压力对海平面的影响几乎完全反映在河流水位的波动上。通过在无风条件和稳定河流流量条件下观测河流水位的数据，可以应用纯粹由流量引起的河流上涨的经验规则，从而提供风和河流行为之间关系的定量估计。然后，利用得到的这四个因子与河面水位的定量关系，估算出某一位置的流量，其结果与观测流量基本一致。这印证了本研究的实践效度。

It is essential to find the correct relationship between flow rate and river level in order to have information about the flow rate during flood and about uses of the river water like agriculture and hydroelectric generation. Normally, the river flow rate is assumed to be given by the level through the empirical H-Q equation, where H is the water level (height) and Q is the flowrate, but during drought, it becomes extremely more difficult to apply this expression to the estuary than to locations upstream. This is because the river level can take a large range of values under the influence of the four key factors of tide, atmospheric pressure, wind direction and wind speed. In this study, it was attempted to derive a method for quantitative estimation of the effects of tide, atmospheric pressure, wind direction and wind speed on flowrate in the estuary of the Ishikari River, where these four factors dramatically lower the correlation between water level (H) and river flowrate (Q). It was found that the effect of tide and atmospheric pressure on sea level is almost exactly reflected in the fluctuations of river level. Data from observations of river level under windless conditions and steady river flowrate allowed application of empirical rules for river rise due purely to flowrate, providing a quantitative estimate of the relation between wind and river behavior. Next, the flowrate was estimated at a certain location using the obtained quantitative relation between the four factors and river level, and this was found to be nearly identical to the observed flowrate. This confirmed the practical validity of this study.