The development of a system capable of distributing water, without shortages or surpluses, to each terminal in a down-stream region is a topic of interest in the context of open channel waterway systems, in which the water demand for agriculture fluctuates considerably. In this study, the optimal combination of inflow amount to the upstream side of the check gate of the main open channel from the pipeline was attempted to be determined for a double-waterway system, in which the pipeline is constructed along the main canal of the long open channel. A type of conjugate gradient method called the Davidon–Fletcher–Powell method was embedded into an unsteady flow program for the open channel, and four types of evaluation functions for water diversion and water level, which incorporate a penalty function corresponding to surplus water and volume of inflow, were introduced to evaluate the degree of achievement with respect to the objective. The effectiveness of the evaluation function was investigated, and the results demonstrated that the inflow stabilized in the order of water diversion ＜ water level ＜ water level + water diversion ＜ water level + surplus water; irrespectively, a favorable result was obtained from each of the evaluation functions. Therefore, the double-waterway system is an ideal system in which the open channel and the pipeline mutually overcome the limitations of each other, and the system is capable of managing the demand fluctuation at the terminals.

  In recent years, heavy rainfall has frequently occurred for the first time in observation history due to climate change associated with global warming. Therefore, in the future, it is important to use rainwater as a water resource and create a town that incorporates groundwater recharge by infiltration of rainwater. To this end, the Architectural Institute of Japan has published "Guideline for Rainwater Harvesting Architecture (AIJES-W0002-2011, AIJES-W0002-2019)" and "Technical Standards for Rainwater Harvesting (AIJES-W0003-2016)". The Guideline for Rainwater Harvesting Architecture specify details on the design, installation, and operation of rainwater harvesting systems according to four basic technologies: rain collection, rain holding, rain control, and rain distribution. The Technical Standards for Rainwater Harvesting proposed a new concept called “Rain Stock” that stores and uses rain on the site. This report introduces each standards, evaluates the performance of rain stock proposed in the Technical Standards for Rainwater Harvesting, and discusses future issues and prospects.

  We investigate the succession of woody vegetation and use our results to predict the occurrence of shallow landslides on susceptible steep slopes in an abandoned forest after plantation clear cutting in Kagoshima Prefecture. We installed quadrats on six slopes to conduct vegetation surveys and measure topsoil thickness: four on steep slopes of ≥40º and two with gentle slopes of ＜20º. The results show that steep slopes have a smaller diameter at chest height, maximum tree height, tree age, number of trees and tree species, chest height cross-sectional area, Fisher-Williams index of diversity, topsoil thickness, and rate of topsoil development than those on gentle slopes. Vegetation was less abundant on steep slopes prone to shallow landslides than on gentle slopes. We also conducted a field survey to predict the occurrence of shallow landslides on steep slopes. The minimum values of topsoil thickness caused by shallow landslides decreased with increasing slope inclination. If the value of topsoil thickness caused by a shallow landslide exceeds the minimum values of topsoil thickness caused by shallow landslides, shallow landslides were generated.

  In the dry field irrigation pipeline, under some mean pressure, it receives repetitive fluctuating pressure due to the operation of the terminal sprinkler. Therefore, even when a pressure lower than the design water pressure is applied, fatigue fracture which is presumed to be caused by the material in the PVC (Polyvinyl chloride) pipe may occur in some cases. Therefore, in addition to the average pressure, the lifetime of the PVC pipe subjected to repetitive oscillating pressures pulsation is predicted using the fatigue crack propagation rate. As a result, the number of life cycles by model calculation is roughly in agreement with the cycle estimated from accident cases of fatigue fracture at the site, and it became clear that lifetime predictions by the crack propagation rate is possible to some extent.

  This study assessed the impact of the small-scale irrigation in the northern area of Zambia, hypothesized that the small-scale irrigation affects not only agricultural production but also the rural livelihood. The impact has been evaluated with comparing quantitative indicators such as cultivated areas, agricultural yield/income, food expenditure/diversification, coping strategy index and children's height/weight between the irrigated areas and non-irrigated areas. This study revealed that the introduction of small-scale irrigation not only has a direct impact on the increase in agricultural production and livelihood improvement, but also has a secondary impact on food diversification/security and nutrition improvement．

  Akashima island, Goto City, in the Nagasaki Prefecture of Japan is a small island (0.54 km²) with approximately 10 residents. The island is the only island in Japan where all domestic water is supplied by rainwater harvesting. The Fukui University of Technology has been implementing the Akashima Revitalization Project since 2016, aiming at the sustainable development of Akashima. As part of the project, a survey on rainwater usage was conducted in Akashima. The survey results indicated that the quality of the stored rainwater was relatively good, and there were no issues with simple filtration and sterilization. The daily water consumption per person was between 50 to 60 L, approximately a quarter of the water used by people living in a general city with water supply (219 L).