Flood Plain Research in Montana with RiverSurveyor

In 1990, noted journalist Charles Kuralt chronicled the discovery, by Flathead Lake Biological Station (FLBS) scientists, of an underground river flowing beneath the flood plain of the Flathead River. Stoneflies and some 40 other species of invertebrates previously unknown to science reside in natural zones of high hydraulic conductivity that channel river water underground, through the alluvial aquifers and back to the surface of the flood plains. This discovery redefined the scientific discipline of river ecology by showing the critical importance of water exchange between the river and adjacent alluvial aquifers. This exchange determines the distribution of riparian plants and creates a complex habitat mosaic, which makes the flood plains regional hotspots of biodiversity.

The key processes that produce and maintain flood plains, composed of zones of preferential underground flow where these organisms reside, are cut and fill alluviation, channel avulsion, and the production and entrainment of large woody debris. Groundwater routing and upwelling is interactive with, and sustained by, cut-and-fill alluviation and successional dynamics of flood plain vegetation such as cottonwood trees. This interaction creates a complex, dynamic array of resource patches and interfaces, thereby producing a regional hot spot of biodiversity. Therefore, alluvial flood plains are regional centers of ecological organization, owing to dynamic, non-linear processes linking water and materials (including biota) flux and retention (surface and subsurface) to interactive landscape-forming processes.

SonTek 3-MHz Mini-ADP RiverSurveyor system
on the Flathead River near Kalispell, MT*

FLBS's use of the SonTek RiverSurveyor ADP stems from their need to measure water depth, flow velocity, and discharge in real-time, in the field, and during the acquisition of airborne remote sensing data. This type of data collection scheme allows FLBS to accurately extrapolate and map flow depth, velocity, shear stress, and stream power for extensive flood plain reaches. Moreover, the data collected with the RiverSurveyor provides the ground-truthing base for FLBS's GIS modeling of changes in potential channel sensitivity and volumetric flux of sediment essential to future sediment budget estimates. Work aimed at identifying these sediment transport issues is the key to understanding the spatial and temporal variability of cut-and-fill alluviation processes that are the driving physical forces for sustaining the ecological health of the river system.

Essentially, FLBS is modeling channel sensitivity to change within river systems by combining remote-sensing and GIS techniques with field-based ground-truthing methods provided by the SonTek RiverSurveyor system. More information of these types of projects and others underway at the University of Montana Flathead Lake Biological Station can be found by visiting their web site at: www.umt.edu/biology/flbs.

*Article and photographs courtesy of the University of Montana Flathead River Biological Station.

• RiverSurveyor