Annual layers in river-bed sediment of a stagnant river-mouth area of the Kitagawa Brook, Central Japan

Y Kurashige,T Nakano,E Kasubuchi,H Domitsu,M Maruo

doi:10.5194/piahs-367-251-2015

Abstract

Abstract. The river mouth of Kitagawa Brook is normally stagnant because it is easily closed by sand and gravel transported by littoral currents of Biwa Lake, Japan. A new urban area exists in the basin and sewerage works were constructed in the early 1990s, so contaminated water with a bad odour had flowed into the brook before the sewerage works. To reduce the smell, the river mouth was excavated to narrow the channel in the early 1980s. Thus, river-bed sediment after this excavation only occurs at the river mouth. From the upper 24 cm of a sediment core, we found 19 strata of leaves which were supplied from deciduous trees in autumn. We also found several gravel layers which were supplied from the lake during severe storms. The combination of veins and gravel layers were reconstructed for about 20 years of sediment records with an error of two to three years.

Highlights

The Kitagawa Brook is a small brook which flows through the new urban area of Hikone City, and into Lake Biwa, the largest lake in Japan
Very contaminated water flowed into the brook, and the citizens of Ooyabu Town living around the river mouth had suffered from the very foul odour of the river water, in summer
The age could not be determined for the layers lower than the 33 cm depth in the core

Summary

Introduction

The Kitagawa Brook is a small brook which flows through the new urban area of Hikone City, and into Lake Biwa, the largest lake in Japan. The river channel of the river-mouth area was artificially narrowed and meandered. Sewerage works were started in the early 1990s and completed in 1998 in this urban area (Hikone City, 2013). Very contaminated water flowed into the brook, and the citizens of Ooyabu Town living around the river mouth had suffered from the very foul odour of the river water, in summer. To take measures to cope with this situation, the local government excavated the river-bed sediment at the river mouth to narrow the water surface in the early 1980s There is no official record of this alteration at Hikone City Hall

Objectives

Conclusion