[A-HW28] Hydrology and Water Environment

[AHW28-P10] Exploring GIS-based soil moisture indices for modeling riparian zone groundwater dynamics in steep headwater catchments of Central Japan

*Aaron Alexander Conte¹, Andrew Charles Whitaker² (1.Graduate School of Science and Technology, Niigata University, Japan, 2.Institute of Science and Technology, Niigata University, Japan)

Keywords:riparian zone, headwaters, water quality, surface-groundwater interactions, soil moisture models

Headwater streams constitute a significant portion of the landscape across various catchment settings, comprising more than 70% of the entire stream network. Due to their unique position at the interface of terrestrial and aquatic ecosystems, riparian areas around headwater streams exert high amounts of influence in the regulation of water quality within these environments. This is one of the main drivers for the establishment of riparian management zones surrounding headwater streams, which normally tend to be outlined as fixed-width protecting vegetation strips. However, further examination has shown that the capacity for water quality regulation is strongly influenced by the hydrological processes occurring at the surface – groundwater interface within riparian zones, and that the properties of these interactions are not homogeneously distributed along the river continuum. Findings suggest the existence of constrained areas along a stream network where groundwater seepage tends to generate disproportionate alterations to the stream water chemistry. Identifying and delineating the extent and spatial distribution of this interface is still a challenge currently being addressed by research, which could contribute to a better understanding of riparian functions and improved utilization of riparian management zones. In this study, we assess the utility of two topography-based soil moisture modelling techniques in mapping and interpreting the characteristics of surface-groundwater interaction zones. The Topographic Wetness Index (TWI) and the Cartographic Depth-to-Water (DTW) Index were estimated by using a 5 m resolution Airborne Laser Survey (ALS) DEM corresponding to a steep headwater catchment area of Central Japan. The values obtained from the models were then compared with continuous water level data collected from groundwater observation wells installed within transects with differing topography. Initial findings suggest that both models are suitable for identifying groundwater seepage points in riparian areas, however, the observed relationship between groundwater levels and model outputs was not constant over time and was also found to differ between monitoring sites. Finally, some considerations about the sensitivity and applications of these soil moisture indices within the study area are provided.