Geology topics

C.P. Konrad

Publications and source records attributed to C.P. Konrad.

5 recordsLinked to original sources

USGS2009

Simulating the recovery of suspended sediment transport and river-bed stability in response to dam removal on the Elwha River, Washington

U.S. Department of the Interior is planning to remove two high dams (30 and 60 m) from the Elwha River, which will allow the river to erode sediment deposits in the reservoirs, and ultimately restore the river ecosystem. Fluvial sediment transport and deposition paradoxically represent ecological disturbance and restoration. A one-dimensional, movable boundary sediment-transport model was applied at a daily time step to simulate changes in river-bed elevations and particle-size distributions and concentrations of suspended sediment. The simulations included a three-year dam removal period and a four-year recovery period. Simulated concentrations of suspended sediment recover rapidly during the recovery period. Simulated bed elevation and particle-size distributions are stable for much of the river during the recovery period, but high flows periodically disturb the river bed, causing changes in river-bed elevation and particle-size distribution, especially during autumn, when summer/autumn chinook salmon are incubating in redds. Although the river bed will become increasingly stable after dam removal, episodic high flows will interrupt recovery trends. Productivity and diversity of the ecosystem may be lower because of excess sediment immediately after dam removal but should increase during recovery above current levels as the river. Monitoring of the recovery of the Elwha River ecosystem can target ecologically significant physical parameters indicating the transition from a sediment transport-limited state to a supply-limited state.

Ecological Engineering↗

USGS2008

Assessing streamflow characteristics as limiting factors on benthic invertebrate assemblages in streams across the western United States

1. Human use of land and water resources modifies many streamflow characteristics, which can have significant ecological consequences. Streamflow and invertebrate data collected at 111 sites in the western U.S.A. were analysed to identify streamflow characteristics (magnitude, frequency, duration, timing and variation) that are probably to limit characteristics of benthic invertebrate assemblages (abundance, richness, diversity and evenness, functional feeding groups and individual taxa) and, thus, would be important for freshwater conservation and restoration. Our analysis investigated multiple metrics for each biological and hydrological characteristic, but focuses on 14 invertebrate metrics and 13 streamflow metrics representing the key associations between streamflow and invertebrates. 2. Streamflow is only one of many environmental and biotic factors that influence the characteristics of invertebrate assemblages. Although the central tendency of invertebrate assemblage characteristics may not respond to any one factor across a large region like the western U.S.A., we postulate that streamflow may limit some invertebrates. To assess streamflow characteristics as limiting factors on invertebrate assemblages, we developed a nonparametric screening procedure to identify upper (ceilings) or lower (floors) limits on invertebrate metrics associated with streamflow metrics. Ceilings and floors for selected metrics were then quantified using quantile regression. 3. Invertebrate assemblages had limits associated with all streamflow characteristics that we analysed. Metrics of streamflow variation at daily to inter-annual scales were among the most common characteristics associated with limits on invertebrate assemblages. Baseflow recession, daily variation and monthly variation, in streamflow were associated with the largest number of invertebrate metrics. Since changes in streamflow variation are often a consequence of hydrologic alteration, they may serve as useful indicators of ecologically significant changes in streamflow and as benchmarks for managing streamflow for ecological objectives. 4. Relative abundance of Plecoptera, richness of non-insect taxa and relative abundance of intolerant taxa were associated with multiple streamflow metrics. Metrics of sensitive taxa (Ephemeroptera, Plecoptera and Trichoptera), and intolerant taxa generally had ceilings associated with flow metrics while metrics of tolerant taxa, non-insects, dominance and chironomids generally had floors. Broader characteristics of invertebrate assemblages such as abundance and richness had fewer limits, but these limits were nonetheless associated with a broad range of streamflow characteristics.

Freshwater Biology↗

USGS2008

Integrating remotely acquired and field data to assess effects of setback levees on riparian and aquatic habitat in glacial-melt water rivers

Setback levees, in which levees are reconstructed at a greater distance from a river channel, are a promising restoration technique particularly for alluvial rivers with broad floodplains where river-floodplain connectivity is essential to ecological processes. Documenting the ecological outcomes of restoration activities is essential for assessing the comparative benefits of different restoration approaches and for justifying new restoration projects. Remote sensing of aquatic habitats offers one approach for comprehensive, objective documentation of river and floodplain habitats, but is difficult in glacial rivers because of high suspended-sediment concentrations, braiding and a lack of large, well-differentiated channel forms such as riffles and pools. Remote imagery and field surveys were used to assess the effects of recent and planned setback levees along the Puyallup River and, more generally, the application of multispectral imagery for classifying aquatic and riparian habitats in glacial-melt water rivers. Airborne images were acquired with a horizontal ground resolution of 0.5 m in three spectral bands (0.545-0.555, 0.665-0.675 and 0.790-0.810 ??m) spanning from green to near infrared (NIR) wavelengths. Field surveys identified river and floodplain habitat features and provided the basis for a comparative hydraulic analysis. Broad categories of aquatic habitat (smooth and rough water surface), exposed sediment (sand and boulder) and vegetated surfaces (herbaceous and deciduous shrub/forest) were classified accurately using the airborne images. Other categories [e.g. conifers, boulder, large woody debtis (LWD)] and subdivisions of broad categories (e.g. riffles and runs) were not successfully classified either because these features did not form large patches that could be identified on the imagery or their spectral reflectances were not distinct from those of other habitat types. Airborne imagery was critical for assessing fine-scale aquatic habitat heterogeneity including shallow, low-velocity regions that were not feasible or practical to map in the field in many cases due to their widespread distribution, small size and poorly defined boundaries with other habitat types. At the reach-scale, the setback levee affected the amount and distribution of riparian and aquatic habitats: (1) the area of all habitats was greater where levees had been set back and with relatively more vegetated floodplain habitat and relatively less exposed sediment and aquatic habitat, (2) where levees confine the river, less low-velocity aquatic habitat is present over a range of flows with a higher degree of bed instability during high flows. As river restoration proceeds in the Pacific Northwest and elsewhere, remotely acquired imagery will be important for documenting its effects on the amount and distribution of aquatic and floodplain habitats, complimenting field data as a quantitative basis for evaluating project efficacy.

River Research and Applications↗

USGS2005

Hydrologic changes in urban streams and their ecological significance

Urban development modifies the production and delivery of runoff to streams and the resulting rate, volume, and timing of streamflow. Given that streamflow demonstrably influences the structure and composition of lotic communities, we have identified four hydrologic changes resulting from urban development that are potentially significant to stream ecosystems: increased frequency of high flows, redistribution of water from base flow to storm flow, increased daily variation in streamflow, and reduction in low flow. Previous investigations of streamflow patterns and biological assemblages provide a scale of ecological significance for each type of streamflow pattern. The scales establish the magnitude of changes in streamflow patterns that could be expected to produce biological responses in streams. Long-term streamflow records from eight streams in urbanizing areas of the United States and five additional reference streams, where land use has been relatively stable, were analyzed to assess if streamflow patterns were modified by urban development to an extent that a biological response could be expected and whether climate patterns could account for equivalent hydrologic variation in the reference streams. Changes in each type of streamflow pattern were evident in some but not all of the urban streams and were nearly absent in the reference streams. Given these results, hydrologic changes are likely significant to urban stream ecosystems, but the significance depends on the stream's physiographic context and spatial and temporal patterns of urban development. In urban streams with substantially altered hydrology, short-term goals for urban stream rehabilitation may be limited because of the difficulty and expense of restoring hydrologic processes in an urban landscape. The ecological benefits of improving physical habitat and water quality may be tempered by persistent effects of altered streamflow. In the end, the hydrologic effects of urban development must be addressed for restoration of urban streams. ?? 2005 by the American Fisheries Society.

American Fisheries Society Symposium↗

USGS2002

Hydrologic trends associated with urban development for selected streams in the Puget Sound basin, western Washington

Annual streamflow statistics from 10 selected streams in the Puget Sound Basin in western Washington were analyzed to identify possible hydrologic trends associated with urban development and to evaluate the effect of record length on errors in trend analysis. The analysis used three common streamflow statistics (annual mean discharge, annual maximum discharge, and 7-day low flow) and introduced an alternative statistic (fraction of year annual mean discharge was exceeded) for assessing the hydrologic effects of urban development. Although trends were identified in each of the four statistics analyzed, trends were not consistent in any of the four statistics for all selected streams. Instead, trends in two statistics ? (1) fraction of year annual mean discharge was exceeded, and (2) annual (instantaneous) maximum discharge ? were evident in streams with the highest levels of urban development over the period of record but not in streams with the lowest levels of urban development. Trends were not consistent for either annual mean discharge or 7-day low flow in urban streams. Trends were sensitive to the period of analysis for all four statistics, but particularly for the 7-day low flow, which showed increasing and decreasing trends for 10 subsets of the period of record in some streams.

Water-Resources Investigations Report↗