[A-CG40] Coastal Ecosystems - 1. Water Cycle and Land-Ocean Interactions

[ACG40-P01] Spatial extent of groundwater-derived heat in coastal area of volcanic sandy beach

*Makoto Yamada¹, Ryo Sugimoto², Toshimi Nakajima² (1.Faculty of Economics, Ryukoku University, 2.Faculty of Marine Biosciences, Fukui Prefectural University)

Keywords:Groundwater, Coastal Area, Heat Influx, Thermal Image, Drone

Fresh groundwater from coastal areas provides nutrients to the sea and influences coastal ecosystems, but such fresh groundwater also provides thermal energy as well as chemical components. In contrast to seawater, groundwater has thermal characteristics that do not change significantly throughout the year. In other words, compared to seawater, cold water flows in during the summer and warm water flows in during the winter. However, the actual situation of the heat supplied by such groundwater is incompletely understood. In this study, we measured the surface temperature distribution of the sandy beach area and the sea area by a drone equipped with a thermal camera at the beach along the coast of Chokai Volcano in August 2020, and verified the spatial extent of groundwater-derived heat. In addition, the amount of heat flowing into the coastal zone was estimated from the freshwater inflow and temperature. Groundwater discharge in the sandy beach area was mainly observed on land, and no discharge from the seabed was observed. Groundwater from the land area flowed a few meters on the surface and then flowed into the sea. The groundwater temperature immediately after the discharge was about 9 deg. C, but it became about 12 deg. C while flowing on the surface and flowed into the sea. In the sea area, the sea water temperature range from 20 to 25 deg. C was extended to about 50 m off the shoreline. Since the actual seawater temperature measured offshore was about 28 deg. C, it is thought that a seawater temperature area of 20 to 25 deg. C was formed due to the low temperature water flowing in from the land. The area of the sea affected by groundwater-derived heat was about 13,000 m² (about 300 m north-south and 50 m east-west).The amount of heat flowing from the groundwater into the sea was estimated to be about -16 GJ/day. These results indicate that groundwater discharged at the sandy beach plays a role in lowering the seawater temperature in a certain range of coastal areas during the summer.