LABS FOR RAINWATER SOCIETY

Hiigawa Terrace is a cafe in the Hii River watershed. In March 2018, watershed area residents and shops took part in a workshop to consider ideas for a rainfall café. Proposed ideas included the installation of a thatched roof made of pergola, the directing of rainwater via a drain spout, and the supplying of rainwater collected in a tank to an aquarium in which fish from the Hii River lived.

 

We organized the ideas to form a plan, and implemented currently feasible items this year. The funding for this implementation came from the research funding for this project as well as funding collected from various sources through crowd funding launched by Kyushu University. Research funding and crowd funding allocation was clearly separated and defined.

The scope of this project was the area used as store space. All of the building's drain spouts discharge into a storm water inlet. The exterior consists of impenetrable concrete and asphalt, as well as tightly packed soil, so almost all of the rain that falls on the soil runs off.

The basic concept of implementation was to create a riverside terrace along the Hii River that would bring people in the watershed area together and foster interaction, and that would store rainwater, curbing runoff as much as possible. The exposed ground area and asphalt parking area, which were relatively easy to modify, were excavated to a depth of 30 cm and a single-sized crushed stone area capable of retaining rainwater was created. The infiltration capacity of the crushed stone base was calculated to be 20 mm/hr. A wood deck was built over the crushed stone layer.

During 100 mm rains, the amount of rainfall on the property was 14.4 m3, and the runoff rate was almost 100%. With the modifications, the runoff rate fell to 50%. The cost of construction was 670,000 yen. At 95,000 yen per 1 m3 of river improvement, this met the target of 100,000 yen / 1 m3. Large scale construction work (soil excavation and crushed stone placement) was performed in conjunction with landscapers, but the deck construction, vegetation planting, etc. were performed by store staff and LRwS and other related parties using a DIY approach.