WORKING THROUGH THE WATER: STREAM BATHYMETRY WITH THE EXPERIMENTAL ADVANCED AIRBORNE RESEARCH LIDAR (EAARL)

The EAARL is a cross-environment, narrow-beam, full-waveform airborne lidar capable of simultaneous surveys of shallow bathymetry, subaerial bare earth topography and the three-dimensional structure of a vegetation canopy. In small clear mountain streams in the Idaho Batholith, the EAARL has demonstrated a scope of 10⁵, with channel bed and bank features having a minimum size of 1-2 m² mapped over channel domains of about 100 km. EAARL data have been used to describe the spatio-temporal distribution of channel morphology and aquatic habitat in this environment, replacing traditional isolated local field-surveyed samples of channel conditions with more nearly complete inventories. The extensive and continuous EAARL stream mapping offers improved opportunities to analyze channel topography and habitat in the frequency domain, and particularly to explore patterns of features with wavelengths much greater than the spatial limit of conventional ground surveys. The data also support mechanistic analyses, using a 2D computational fluid dynamics model, of potential climate change effects on the viability of salmon and steelhead egg nests due to increased channel bed mobility and sand transport. The EAARL is currently being upgraded to have six-times greater data spatial density as well as improved water penetration and depth discrimination, using a laser with a five-fold increase in power and one-half the previous pulse width. This new ability to map large portions of stream networks and floodplains challenges us to think beyond conventional channel cross sections and short reaches of streams, and instead to describe and investigate channel and riparian processes, forms and spatial patterns of habitat at up to watershed scales.