The concept of groundwater governance has taken over the discussion of Integrated Water Resource Management centered on stakeholder participation and cross-sector integration. The Groundwater Governance Project by Global Environmental Facility and other international organizations from 2011 to 2014 comprehensively reviewed the current status of groundwater governance all over the world and concluded that it is still far from an ideal state. In the case of Japan,top-down regulations by national and local governments have been the main way for groundwater management traditionally. However, there have been moves to adopt the concept of groundwater governance recently. This paper gives a brief overview of groundwater management in Japan based on "four components of governance" by the Groundwater Governance Project - actors; legal, regulatory and institutional frameworks; goals, policies and plans; and information, knowledge and science - and discusses the significance and issues of introducing the concept of groundwater governance.

In recent years, increasing attention has been paid to the involvement of various stakeholders in groundwater conservation. Because of the importance of this trend, this paper aims to clarify what existing consensus-building studies imply for groundwater governance. First, we reviewed consensus building studies, assessing the main concerns and the relationship to groundwater governance studies. Then, factors which promote consensus-building were investigated through case studies in the fields of social dilemma, project-management and commons studies. The comparative study showed that the following factors played important roles in consensus-building; framing, policy combination, and providing for multiple goals for stakeholders with plural values. Finally, we considered how these factors could be applied to groundwater governance.

This article focuses on the governance dynamics of groundwater which means a change of structure and function of groundwater governance over time. Based on a change (multiple stratification) of policy agenda on groundwater in Japan, we suggest that social value of groundwater is a key concept to grasp related cases comprehensively. The types of reaction to social value include countermeasures against social loss, avoidance of social loss and creation of social value. We clarify the degree of groundwater governance is stronger with expansion of those types of social value. A change of groundwater management is another topic, we clarify how that change reflects the characteristics of groundwater governance which consist of multi-actor, multi-level and policy mix through some case studies of groundwater infrastructure.

As one of the recent activities, JAGH (Japanese Association of Groundwater Hydrology) established the groundwater governance research group. It investigates the policies and sustainable groundwater use governance in relation to the Basic Plan on Water Cycle Policy. The research is conducted with a certain scope on social scientific aspects. The research group (Group C: 15 members) is manly focused on domestic case studies. Present work represents a study on 65 individual cases collected from 58 provinces. The case studies were compiled and characterized with some basic clustering criteria.

I began my career with the Geology Laboratory of the Railway Technical Research Institute of the Japan National Railways. Most of my jobs for more than 55 years since then are related to tunnel construction, especially with difficulties arisen from groundwater inflow. As I had the opportunity to present the article for the special issue 'Tunnel' of the Journal of Groundwater Society, essences of what I have learned and experienced with regard to groundwater inflow to tunnels are introduced with some of the case studies. Firstly, an overview on the "Fundamentals of groundwater inflow" is explained, such as classification and treatment of water inflow, concept of perpetual water inflow in tunnel with its origin, and the reason why difficulties of tunnel construction is proportional to the amount of water inflow and level of ground pressure. Then, various findings through my research on water inflow and tunnels are introduced, such as systemization of hydrological survey methods, how to select tunnel route, construction methodology of tunnel and effective use of tunnel water inflow, interrelation between tunnel and dam when constructed adjacent to dam, and water quality of tunnel inflow. I hope this article may be helpful to those researchers and engineers involved in tunnel construction.

Author explained the influence of the construction of tunnels and underground structures on the groundwater environment, and the influence of groundwater on the tunnel construction, based on past cases. In addition, an overview of the history of new construction techniques that have been developed so far to prevent the adverse effects of tunnel construction on the groundwater environment was also presented. In particular, author described various construction methods for each of the water cut-off method and drainage method,their difficulties, and how to use them properly according to the situation at the site.

A 3D numerical model was developed to simulate seawater intrusion and aquifer recovery in Niijima Island under the future Nankai earthquake and tsunami scenario. The FEFLOW code was used to solve density-dependent groundwater flow and mass transport in unsaturated-saturated porous media. The simulations indicated that the maximum amount of seawater intrusion during the tsunami was controlled by the total unsaturated void space of the soil beneath the inundation area. After the tsunami, directions of seawater movement and flushing time depended on the pre-tsunami groundwater flow conditions and bedrock structures. Some groundwater was found to be survived from salinization, and showed the potential to provide water supply in an equivalent amount of the pre-tsunami level without worsening the recovery process. The simulated attempt to remove the intruded seawater from a polluted well could accelerate aquifer recovery but might not be practical due to the cost of maintaining intensive pumping over years.