Decision Making for a Small Sewerage Plan by Estimation of the Influence of a Population Decrease on Total Cost

Study on planning small sewerage systems in rural areas (II)

Abstract

Recently, a master plan for sewerage construction, for complete coverage of city, town and village areas has been devised in Japan. This plan has be able to make progress regarding the construction of small sewerage systems in rural areas.
One of the purposes of this plan is to make sewerage disposal as economical as possible. The economical estimation of sewerage construction is made on the assumption that population of each district will increase. Therefore, the economical influence due to the decrease in the population is not considerd exactly. However, in rural areas, a decrease in population happens in general.
Economical estimation changes for the worse, as the population decreases. The effect of a decreasing population on the economical estimation is different between each sewerage system. So that a suitable sewerage system for a district changes as the population decreases. Then, we must consider the features of a population district, when we plan sewerage construction from the economical point of view.
In this paper, authors discussed three points.
1. Analysis on the character of population changes in rural areas.
2. Analysis on the economical estimation under the condition of a decreasing population.
3. Suggestions on how to make a master plan in population decreasing area, from the economical point of view.