Author(s)

K. Yokoo, S. Yoshida, C. P. Caulfield, P. F. Linden & I. Ito

Abstract

Generally, the response of the river water level in an estuary to the river flowrate is far from simple. The main reasons for this are the four competing factors of tide, atmospheric pressure, wind direction and wind speed, whose effects drive the river level to a variety of elevations. The error represented by the average of that dispersed group can at times be over 200%. No matter what statistical analysis is applied, no plausible estimate of the flowrate can be made from the river level alone. This paper uses data taken in the Ishikari River estuary over the last 5 years to present a quantitative relationship of the above 4 factors on the level of the Ishikari River. These relationships permit highly precise calculation of the river flowrate, using observed values of the above 4 factors, at any arbitrary location in the estuary. Keywords: estuary, river mouth, two-layer flow, river level, tidal river, flowrate, H-Q curve. 1 Introduction It has been over 60 years since the inaugural research into highly stratified rivers in Japan with observations of the salt wedge in the Ishikari Estuary in 1939 (Fukushima [2]). Stratified flow problems are far better known now, and a large number of researchers have provided a generous fund of data on stratified flows in estuaries and the littoral zone (Dyer [1]; Officer [5]; Manual of Hydraulic Engineering [4]; Yoshida [8]). However, some reflection on the currently available results will show that even though it has become possible to predict the shape of the salt wedge in quasi-steady flow, nearly all real estuarine flows are not quasi-steady, because of the various factors influencing real rivers. It is difficult to say that previous research has been that helpful for practical river management. The main reason for this impasse is the great expense of field

Keywords

estuary, river mouth, two-layer flow, river level, tidal river, flowrate, H-Q curve.