Climate, Hydrologic Disturbance, and Succession: Drivers of Floodplain Pattern

Floodplains are among the world\u27s most threatened ecosystems due to the pervasiveness of dams, levee systems, and other modi. cations to rivers. Few unaltered floodplains remain where we may examine their dynamics over decadal time scales. Our study provides a detailed examination of landscape change over a 60-year period ( 1945 - 2004) on the Nyack floodplain of the Middle Fork of the Flathead River, a free-flowing, gravel-bed river in northwest Montana, USA. We used historical aerial photographs and airborne and satellite imagery to delineate habitats ( i.e., mature forest, regenerative forest, water, cobble) within the. oodplain. We related changes in the distribution and size of these habitats to hydrologic disturbance and regional climate. Results show a relationship between changes in. oodplain habitats and annual flood magnitude, as well as between hydrology and the cooling and warming phases of the Pacific Decadal Oscillation (PDO). Large magnitude floods and greater frequency of moderate floods were associated with the cooling phases of the PDO, resulting in a floodplain environment dominated by extensive restructuring and regeneration of floodplain habitats. Conversely, warming phases of the PDO corresponded with decreases in magnitude, duration, and frequency of critical flows, creating a floodplain environment dominated by late successional vegetation and low levels of physical restructuring. Over the 60-year time series, habitat change was widespread throughout the floodplain, though the relative abundances of the habitats did not change greatly. We conclude that the long- and short-term interactions of climate, floods, and plant succession produce a shifting habitat mosaic that is a fundamental attribute of natural. oodplain ecosystems

Potential sedimentation impacts related to dam removal: Icicle Creek, Washington, U.S.A.

A series of small dams were built in Icicle Creek in 1937 to facilitate the operations of Leavenworth National Fish Hatchery. However, several of those dams have been abandoned spurring recent discussions among local watershed conservation groups, as well as state and federal agencies, about removing the dams and the potential impact to the lower reaches of Icicle Creek due to elevated sedimentation. The objective of this study was to measure the total volume of sediment trapped behind the Icicle Creek dams and estimate the potential sedimentation impacts for the lower portion of Icicle Creek should the dams be removed. Another objective was to assess the ability of the river to flush the sediments and naturally restore the system to as close to its predam condition as possible. A flow-competence approach was used to assess the restoration potential of the river to do the work of flushing sediments and reestablishing the predam stream channel characteristics. A sediment probe, a total station, a GPS and aerial photographs were used to map out sediment deposits and measure their depths to determine sediment volumes. Grain size distributions from bed sediments, bars, islands and stream banks were used to assess potential downstream sedimentation impacts. The total volume of sediment trapped behind the dams was estimated at 36,000 m3 (± 4000 m3). The river has sufficient stream power to flush these sediments over 90% of its natural discharge regime. Controlled flushing of the trapped sediments over several years poses very little threat to the water quality and spawning habitats in the lower Icicle Creek scaled against natural flux rates

A flume experiment to examine underwater sound generation by flowing water

ISSN:1015-1621ISSN:1420-905

Field-based observation of the entrainment threshold of cobbles with motion loggers

Beaches composed of pebble to boulder-sized material are a common feature of coastal regions and provide effective protection against wave attack. The wave-related entrainment threshold of these coarse particles is of utmost importance to defining the onset of dynamic beach behavior. Wave-competence equations derived to predict the boundary between particle stability and entrainment when acted on by waves (e.g. Lorang, 2000) are useful when designing artificial gravel beaches as shore protection structures because they help inform the size of material required to mimic the dynamic behavior of their natural counterpart. The objective of this study is to use motion loggers embedded within native cobbles to measure the entrainment threshold during storm wave events to provide much-needed field data with which to test the accuracy of the Lorang (2000) equations. The movement of 14 cobbles were observed over a range of conditions (0.10 m < HS < 0.52 m) during five separate 1.5-hour-long experiments on coarse pebble/cobble beach at Flathead Lake, Montana, USA. The entrainment threshold was positively related to wave power and was accurately predicted by the Lorang (2000) equations using significant wave height, mean period and beach slope to estimate swash velocities and run-up height as driving variables. More experiments are required to constrain the value(s) used for the beach stability coefficient Kr, although the values found here correspond with the widely used Hudson Formula (Hudson, 1952). Alternatively, directly quantifying swash velocities and run-up elevations from video analysis would greatly improve the results rather than estimating these primary variables. These results provide a unique insight into the wave-competence approach to designing dynamic revetments and artificial gravel beaches as shore protection alternatives to rip-rap and seawalls at a time when rising sea level and a potential increase in storm intensity are likely to increase the wave impact on coastal regions

Remote sensing analysis of physical complexity of North Pacific Rim rivers to assist wild salmon conservation

Salmon populations are highly variable in both space and time. Accurate forecasting of the productivity of salmon stocks makes effective management and conservation of the resource extremely challenging. Furthermore, widespread and consistent data on the productivity of species-specific and total salmon stocks in a river are almost nonexistent. Ranking rivers based on physical complexity derived from remote sensing allows rivers to be objectively compared. Our approach considered rivers with great geomorphic complexity (e.g. having expansive, multichanneled floodplains and/or on-channel lakes) as likely to have greater productivity of salmon than rivers flowing in constrained or canyon-bound channels. Our objective was to develop a database of landscape metrics that could be used to rank the rivers in relation to potential salmon productivity. We then examined the rankings in relation to existing empirical (monitoring) data describing productivity of salmon stocks. To extract the metrics for each river basin we used a digital elevation model and multispectral satellite imagery. We developed procedures to extract channel networks, floodplains, on-channel lakes and other catchment features; variables such as catchment area, channel elevation, main channel length, floodplain area, and density of hydrojunctions (nodes) were measured. We processed 1509 catchments in the North Pacific Rim including the Kamchatka Peninsula in Russia and western North America. Overall, catchments were most physically complex in western Kamchatka and western Alaska, and particularly on the Arctic North Slope of Alaska. We could not directly examine coherence between potential and measured productivity except for a few rivers, but the expected relationship generally held. The resulting database and systematic ranking are objective tools that can be used to address questions about landscape structure and biological productivity at regional to continental extents, and provide a way to begin to efficiently prioritize the allocation of funding and resources towards salmon management and conservation