Recently, a lot of researchers have been interested in `scale issues' in the research area of hydrology. 'Scale issues' include various questions to be solved, including lots of issues regarding runoff process. For example, the relationships between some hydrological processes which control runoff process and catchment scale have been studied. Recently, some researchers have tried to clarify the runoff system using mean annual flood (MAF) per unit area and coefficient of variation (CV) of annual flood.In this study, analysis of runoff process by CV and MAF was carried out. First, CV/MAF versus catchment area were plotted for 285 catchments in Japan. Secondly, Eagleson's method was used in order to calculate MAF and CV. The aim of this study is to develop model for numerical analysis of runoff, which will be combined to analysis by the data of 285 catchments. The model used in this study could estimate MAF qualitatively, but further consideration is necessary in regard to CV.

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Some diseases in Myanmar during the rainy season are related to the water environment and the water quality. In order to contribute to ensuring safe water supply, we collected and analyzed water samples in Myanmar in September 2011. Early research had already reported that coliform and E. Coli were detected in all the survey areas. We examined the water quality, especially chemical components harmful for health, and classified the sample waters into water quality-types in order to identify the sources and contamination. We obtained the following results: (1) Some tube well, dug well, and filtered waters were estimated to be contaminated and unsuitable for drinking and domestic water. (2) Waters at elevation less than about 10 m were more likely to be polluted. (3) The chemical components beyond the drinking water guideline values of World Health Organization (WHO) for health were NO 2 -, NO 3 -, Pb 2+ , and Mn 2+ . (4) For the taps with longer direct distance from the pumping station and lower elevation, there were several cases in which the tube well water geographically close to the tap intruded into the tap of filtered water. Then, we suggested some recommendations for water treatment based on WHO guidelines, and we also suggested the desirable improvements to the water supply systems. The first potential approach to treatment of drinking water supplies is to dilute the contaminated water with a low-contaminated source (e.g., high-elevation reservoirs). The desirable improvement to the water supply systems are as follows: (a) piping routes from reservoir to user places should be maintained as sanitary and clean, and (b) tube well water systems should be improved to prevent the intrusion of contaminants.

Abstract:Eagleson's classical regional flood frequency model is investigated. Our intention was not to improve the model, but to reveal previously unidentified important and dominant hydrological processes in it. The change of the coefficient of variation (CV) of annual maximum discharge with catchment area can be viewed as representing the spatial variance of floods in a homogeneous region. Several researchers have reported that the CV decreases as the catchment area increases, at least for large areas. On the other hand, Eagleson's classical studies have been known as pioneer efforts that combine the concept of similarity analysis (scaling) with the derived flood frequency approach. As we have shown, the classical model can reproduce the empirical relationship between the mean annual maximum discharge and catchment area, but it cannot reproduce the empirical decreasing CV-catchment area curve. Therefore, we postulate that previously unidentified hydrological processes would be revealed if the classical model were improved to reproduce the decreasing of CV with catchment area. First, we attempted to improve the classical model by introducing a channel network, but this was ineffective. However, the classical model was improved by introducing a two-parameter gamma distribution for rainfall intensity. What is important is not the gamma distribution itself, but those characteristics of spatial variability of rainfall intensity whose CV decreases with increasing catchment area. Introducing the variability of rainfall intensity into the hydrological simulations explains how the CV of rainfall intensity decreases with increasing catchment area. It is difficult to reflect the rainfall-runoff processes in the model while neglecting the characteristics of rainfall intensity from the viewpoint of annual flood discharge variances.