Using UAV-Based Remote Sensing and Ground-Based Sampling to Characterize Riparian Vegetation and Estimate its Effect on Hyporheic Zone Hydrology

Abstract:

Rangeland watersheds are home to many small headwater streams that contribute a large portion of water to the arid and semiarid ecosystems of the western United States. Improved management of these headwater streams is imperative to the conservation of water resources in rangelands, resources that are experiencing increasing pressure by human migration into these ecosystems. Currently, there is a need for an improved understanding of how vegetation affects hyporheic zones and water balances in rangeland riparian areas. This study examines two methods for producing metrics valuable to understanding the influence of riparian vegetation on hyporheic zones over six stream reaches in a small watershed in the Laramie mountain range in southeastern Wyoming. Four of the reaches feature willows in the riparian areas, while two reaches do not have significant riparian vegetation beyond grasses. To directly link riparian vegetation characteristics and hyporheic zone hydrology, we characterized the type and distribution of riparian vegetation with remote sensing and ground-based sampling methods, then compared those characteristics with hydrologic observations obtained from a series of instrumentation including soil moisture sensors, shallow groundwater wells, and stilling wells. Remote sensing of the reaches was performed using a small Unmanned Aerial Vehicle (sUAV) and cameras for capturing RGB, thermal, and multispectral imagery. High resolution RGB imagery allowed for derivation of a digital surface model, multispectral imagery was used to calculate vegetation indices such as NDVI and EVI, and thermal imagery was used to obtain evapotranspiration estimates in conjunction with observations from a nearby meteorological tower. Ground-based sampling methods, including line-point intercept and modified belt transects, are used to assess canopy cover and vegetation type, structure, and distribution. This study will describe the potential for drone-based research approaches for rangeland eco-hydrologic studies and management applications.