Hydrologieal Investigations of the Takase River, Yamagata City

Abstract

The determination of mineral discharge from the catchment area of a river is fundamentally a matter of hydrology. The purpose of the paper is to discuss the mechanism of the transportation of the dissolved minerals that applies to the erosion by dissolution and at the same time to describe the quality-of-water under hydrological considerations. Data presented herein were collected once a week from the Takase River at Hiraishimizu, Yamagata City during the period 1964-1966.
The observation of the water temperature during the period 1964-1965, reveals the linear relationship of this and the dissolved oxygen. This can be represented by
DO=13.97-0.290Tw
where DO=dissolved oxygen in ppm
Tw=water temperature in °C.
Moreover, during spring months the days of high temperatures and thaws may be reflected by increase in stream flow and by elevation in water temperature as expressed by the equation :
log₁₀ Q=0.93Tw-0.475,
where Q=stream flow in m³/sec
Tw=water temperature in °C.
The amounts of dissolved minerals are in the order : Ca²⁺>Na⁺>Mg²⁺ and HCO₃^->Cl^->SO₄^2-. A linear relationship is found to exist between Ca²⁺ concentration and pH 4.3 alkalinity (Bx). This can be readily computed as follows :
(Ca²⁺) =0.67 Bx+0.11
where each quantity is expressed in meq/1.
The transportation of various dissolved minerals was examined for the 1965 water year. A simple relation is found in each of dissolved minerals in a manner analogous to the transportation of suspension
Q_d=aQⁿ
where Q_d is each mineral discharge and a and n are constants characteristic of each constituent. The same is the case with the total mineral discharge and the following equation is obtained :
Q_ds=47.4Q^0.793
where Q_ds=total mineral discharge in g/sec
Q=flow rate in m³/sec.
The total mineral discharge for the present water year is estimated to be fifteen hundred tons per year.