Effects of reservoir shape on musty odor occurrence

Abstract

The Izari River Dam reservoir has a distinctively shaped bottom, and the Takisato Dam reservoir has a distinctively shaped shoreline. We conducted observations and two-dimensional vertical model simulations in order to (1) identify the effects of shape on flow regime, water temperature, and water quality components, (2) examine the behavior of ray fungi and blue-green algae, which cause musty odor, and (3) understand how odoriferous materials, geosmin and 2-methyl-isoborneol (2-MIB), are formed and released. For the Izari River Dam it was found that water flow toward the surface intake predominates when there were riffles at the upstream part of the reservoir (data of 2000); thus, vertical circulation was weaker when there were riffles than when there were not (data of 1981). This suggests that the release of geosmin involves stagnancy of flow, followed by formation of an anaerobic layer and then death of ray fungi. For Takisato Dam it was found that the increase of water temperature, the proliferation of blue-green algae and generation of 2-MIB are promoted in stagnant water areas at the upstream and downstream parts of the reservoir. The stagnant area forms because the water velocity decreases at the wider part of the reservoir and because the reservoir narrows and curves at the middle. By understanding the relationship between reservoir shape and water flow, a possible way of limiting the musty odor was found.