Three-dimensional mapping of geomorphic controls on flood-plain hydrology and connectivity from aerial photos

Abstract The Nyack flood plain of the Middle Fork Flathead River, MT, USA is a 9-km anastomosed alluvial montane flood plain. Upstream from the flood plain, the river is unregulated and the catchment virtually pristine. A patchy mosaic of vegetation and channels exists on the flood-plain surface. The surface and subsurface geomorphic structures of the flood plain facilitate high hydrologic connectivity (water flux between the channel and flood plain) marked by complex seasonal patterns of flood-plain inundation, extensive penetration of channel water laterally into the alluvial aquifer, and springbrooks formed by ground water erupting onto the flood-plain surface. After delineating and classifying flood-plain “elements” (vegetation patches and channel reaches) on the flood plain, we analyzed field-based elevation survey data to identify expected relationships among flood-plain element type, surface scour frequency, and flood-plain elevation. Data analyses show that scour frequency was inversely proportional to the elevation of the flood plain above river stage, except when localized geomorphic controls such as natural levees prevent normal high flows from inundating and scouring relatively low flood-plain elements. Further, while different flood-plain element types occupy distinct elevation zones on the flood plain, the elevation of each zone above the river channel varies with localized channel entrenchment. We found that topographic variation among flood-plain elements is greater than the variation within elements, suggesting that coarse-scale flood-plain topography can be characterized by delineating flood-plain elements. Field data document strong associations between specific classes of flood-plain elements and preferential ground-water flow paths in the upper alluvial aquifer. Combined with preexisting ground penetrating RADAR (GPR) surveys, these data intimate a sinuous lattice of preferential ground-water flow paths (buried abandoned streambeds) in the upper alluvial aquifer at approximately the same elevation as the main channel's streambed. Using aerial photo interpretation and the identified relationships among element-types, elevation, and preferential ground-water flow paths, we developed a quantitative, three-dimensional characterization of surface and subsurface geomorphology across the entire flood plain to support a heuristic modeling effort investigating the influence of flood-plain geomorphology on spatio-temporal patterns of surface and ground-water flow and exchange under dynamic hydrologic regimes.

[1]  Frederick J. Swanson,et al.  Floods, channel change, and the hyporheic zone , 1999 .

[2]  D. Hannah,et al.  Wood storage within the active zone of a large European gravel-bed river , 2000 .

[3]  J. Stanford,et al.  The hyporheic habitat of river ecosystems , 1988, Nature.

[4]  J. Ward.  RIVERINE LANDSCAPES: BIODIVERSITY PATTERNS, DISTURBANCE REGIMES, AND AQUATIC CONSERVATION , 1998 .

[5]  H. Piégay,et al.  Large woody debris and river geomorphological pattern: examples from S.E. France and S. England , 1997 .

[6]  JamesV. Ward,et al.  An Expansive Perspective of Riverine Landscapes: Pattern and Process Across Scales , 1997 .

[7]  J. Mathieu,et al.  Groundwater/surface water ecotones : biological and hydrological interactions and management options , 1997 .

[8]  D. Montgomery,et al.  LARGE WOODY DEBRIS JAMS, CHANNEL HYDRAULICS AND HABITAT FORMATION IN LARGE RIVERS , 1996 .

[9]  Georgia L. Case.  Distribution and abundance of zoobenthos in channel springbrook and hyporheic habitats of an alluvial floodplain , 1995 .

[10]  G. Malanson,et al.  A major sediment pulse in a subalpine river caused by debris flows in Montana, USA , 1996 .

[11]  R. W. Fonda,et al.  Forest Succession in Relation to River Terrace Development in Olympic National Park, Washington , 1974 .

[12]  G. Malanson,et al.  Floristic Variation Among Gravel Bars in a Subalpine River, Montana, USA. , 1991 .

[13]  Michael E. Campana,et al.  Seasonal variation in surface‐subsurface water exchange and lateral hyporheic area of two stream‐aquifer systems , 1998 .

[14]  S. Walsh,et al.  An overview of scale, pattern, process relationships in geomorphology: a remote sensing and GIS perspective , 1998 .

[15]  S. Fisher,et al.  Multiscale effects of surface–subsurface exchange on stream water nutrient concentrations , 2001, Journal of the North American Benthological Society.

[16]  R. Beschta,et al.  Abiotic aspects of channels and floodplains in riparian ecology , 1998 .

[17]  M. Brunke,et al.  The ecological significance of exchange processes between rivers and groundwater , 1997 .

[18]  Ward,et al.  Biodiversity: towards a unifying theme for river ecology , 2001 .

[19]  J. Kollmann,et al.  Large wood retention in river channels: the case of the Fiume Tagliamento, Italy , 2000 .

[20]  J. Bravard,et al.  6 – Geomorphology of Alluvial Groundwater Ecosystems , 1994 .

[21]  K. Tockner,et al.  Aquatic habitat diversity along the corridor of an Alpine flood plain river (Fiume Tagliamento, Italy)n , 2000 .

[22]  R. Naiman,et al.  Groundwater/Surface Water Ecotones: Biological and Hydrological Interactions and Management Options: Uses and limitations of ground penetrating RADAR in two riparian systems , 1997 .

[23]  J. Stanford,et al.  Microbial respiration within a floodplain aquifer of a large gravel‐bed river , 2002 .

[24]  G. Poole.  Analysis and dynamic simulation of morphologic controls on surface- and ground-water flux in a large alluvial flood plain , 2000 .

[25]  B. K. Ellis,et al.  Microbial Assemblages and Production in Alluvial Aquifers of the Flathead River, Montana, USA , 1998, Journal of the North American Benthological Society.

[26]  Bradley J. Cavallo.  Floodplain habitat heterogeneity and the distribution abundance and behavior of fishes and amphibians in the Middle Fork Flathead River basin Montana , 1997 .

[27]  B. K. Ellis,et al.  14 – Ecology of the Alluvial Aquifers of the Flathead River, Montana , 1994 .

[28]  H. B. N. Hynes,et al.  The stream and its valley , 1975 .

[29]  J. Sharp,et al.  On the relationship between river-basin geomorphology, aquifer hydraulics, and ground-water flow direction in alluvial aquifers , 1992 .

[30]  G. Malanson,et al.  Woody debris, sediment, and riparian vegetation of a subalpine river, Montana, U.S.A , 1990 .

[31]  G. Nanson,et al.  ANABRANCHING RIVERS: THEIR CAUSE, CHARACTER AND CLASSIFICATION , 1996 .

[32]  D. Sear.  River restoration and geomorphology , 1994 .

[33]  K. Tockner,et al.  SHIFTING DOMINANCE OF SUBCATCHMENT WATER SOURCES AND FLOW PATHS IN A GLACIAL FLOODPLAIN, VAL ROSEG, SWITZERLAND , 1999 .

[34]  F. Swanson,et al.  An Ecosystem Perspective of Riparian ZonesFocus on links between land and water , 1991 .

[35]  J. Stanford,et al.  An Ecosystem Perspective of Alluvial Rivers: Connectivity and the Hyporheic Corridor , 1993, Journal of the North American Benthological Society.