Downstream Effects of the Pelton-Round Butte Hydroelectric Project on Bedload Transport, Channel Morphology, and Channel-Bed Texture, Lower Deschutes River, Oregon (original) (raw)
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Field, laboratory, and historical data provide the basis for interpreting the effects of the Pelton-Round Butte darn complex on the surface water hydrology and geomorphology of the lower Deschutes River, Oregon, USA. The river's response to upstream impoundment and flow regulation is evaluated in terms of changes in predicted bedload transport rates, channel morphology, and channel-bed texture. Using a hydraulic model, we predicted discharges between 270 and 460 m3ls would be required to initiate bedload transport. Analysis of morphologic change at a long-term cross-section showed general scour and fill beginning at approximately 250 m3/s. Such bed-mobilizing flows have occurred less than 1 % of the time dwing the 7W-year period of record, substantially less frequently than on other alluvial rivers. Historical streamflow records and bedload tramport modeling suggest dam operations have had only minimal effects on the fkquency and magnitude of streamflow and bedload transport. Analysis of gage data collected just below the d a m complex revealed slow, minor degradation of the channel over the entire period of record, indicating the dams have not noticeably accelerated long-term incision rates. The dams also have had only minimal effect on channel-bed texture, as demonstrated by detailed analysis of longitudinal trends in surface and subsurface grain-sizes and bed armoring. This study presents a coherent story of the Deschutes River as a stable alluvial system. This stability appears to be due to a hydrologically uniform flow regime and low rates of sediment supply, neither of which has been substantially altered by the dams or their operation.
2003
Within the Deschutes River basin of central Oregon, the geology, hydrology, and physiography influence geomoqhic and ecologic processes at a variety of temporal and spatial scales. Hydrologic and physiographic characteristics of the basin are related to underlying geologic materials. In the southwestern part of the basin, Quaternary volcanism and tectonism has created basin fills and covered and deranged the surficial hydrologic system, resulting in a relatively low-relief lava-covered landscape with runoff emerging largely from extensive groundwater systems fed by Cascade Range precipitation. The remarkably steady flows of the entire Deschutes River, as depicted in annual and peak flow hydrographs, are due primarily to buffering by the extensive groundwater system of this part of the basin. The eastern part of the basin is primarily underlain by Tdary volcanic, volcaniclastic, and sedimentary rocks that have weathered into dissected uplands with generally greater slopes and drainage densities than of that of the southwestern part of the basin. Surficial runoff is more seasonal and less voluminous from this more arid part of the basin. The northern part of the basin has been sharply etched by several hundred meters of late Cenozoic incision, resulting in the greatest relief and drainage density of anywhere in the basin.
Beaver dams and channel sediment dynamics on Odell Creek, Centennial Valley, Montana, USA
Geomorphology, 2014
Beaver dams in streams are generally considered to increase bed elevation through in-channel sediment storage, thus, reintroductions of beaver are increasingly employed as a restoration tool to repair incised stream channels. Here we consider hydrologic and geomorphic characteristics of the study stream in relation to in-channel sediment storage promoted by beaver dams. We also document the persistence of sediment in the channel following breaching of dams. Nine reaches, containing 46 cross-sections, were investigated on Odell Creek at Red Rock Lakes National Wildlife Refuge, Centennial Valley, Montana. Odell Creek has a snowmelt-dominated hydrograph and peak flows between 2 and 10 m 3 s −1 . Odell Creek flows down a fluvial fan with a decreasing gradient (0.018-0.004), but is confined between terraces along most of its length, and displays a mostly single-thread, variably sinuous channel. The study reaches represent the overall downstream decrease in gradient and sediment size, and include three stages of beaver damming: (1) active;
Dams and geomorphology: Research progress and future directions
Dams impose changes of flow and sediment transfer that drive changes of channel form along the downstream regulated river. These changes have been described for more than 50 years but process-form relationships have only been advanced with the establishment of a conceptual framework during the 1970s, and then the extension of monitoring data and advancement of remote sensing technologies, particularly over the past 20 years. This paper reviews these developments and identifies three influential themes: (i) channel dynamics, (ii) the role of riparian vegetation, and (iii) channel change as the driver of ecological change. Changes can be rapid in semi-arid regions but elsewhere relaxation periods may extend to millenia. In these latter cases regime or steady-state models should be replaced by models of transient states applied to the reach scale in order to respond to the needs of river managers over decadal timescales.
Run-of-the-river dams (RORDs) comprise the vast majority of dams on river systems and are commonly removed as a part of stream restoration strategies. Although these dams are routinely removed, few studies have documented the geomorphological responses of sand-bed rivers to the removal of RORDs. We examined the response of a large sand-bed river located in South-Central Kansas, USA, to the installation and removal of a dam that is installed annually for seasonal recreational purposes. Channel adjustments were tracked using cross-sections sampled over the course of 7 months as the dam was installed and subsequently removed. Multivariate spatiotemporal analysis revealed emergence of channel stability when the dam was in place for most cross-sections, except for those immediately adjacent to or at great distances from the dam. Our results provide an approximation for how sand-bed rivers respond to RORD construction and removal and are useful for guiding management decisions involving preservation or restoration of connectivity. Results of this study suggest that sand-bed rivers are resilient and recover quickly when transient RORDs are removed. Figure 3. Photographs of the (A and B) permanent I-beams that are in the channel year round that provide foundation for the dam, (C) the installed dam with planks of wood until the dam is 1 m in height and (Cand D) of the dam spanning the entire channel width. Photographs (B) and (D) were taken from the same vantage point. This figure is available in colour online at wileyonlinelibrary.com/journal/rra Figure 5. Bedform morphology changes of the upstream section South Fork Ninnescah River for the surveying period. This figure is available in colour online at wileyonlinelibrary.com/journal/rra Figure 6. Bedform morphology changes of the downstream section the South Fork Ninnescah River for the surveying period. This figure is available in colour online at wileyonlinelibrary.com/journal/rra RESPONSE OF A SAND-BED RIVER TO RORD Figure 7. Channel cross-sectional profiles for the upstream reach where the left is the North bank and the right is the South bank of the South Fork Ninnescah River. Cross-sections are numbered where +10 is the first cross-section approached moving upstream and +90 is the furthest upstream from the dam and the upper end of the surveying reach Figure 8. Channel cross-sectional profiles for the downstream reach where the left is the North bank and the right is the South bank of the South Fork Ninnescah River. Cross-sections are numbered where À10 is the first cross-section approached moving upstream and À270 is the furthest upstream from the dam and the lower end of the surveying reach Figure 9. Principal component analysis for the first two axes of (A) geomorphic variables and the spatiotemporal effects of the dams for all surveying campaigns for (B) +/À10 m, (C) +/À30 m, (D) +/À50 m, (E) +/À70 m, (F) +/À90 m and (G) À140 m, À190 m, À240 m and À290 m RESPONSE OF A SAND-BED RIVER TO RORD
Sediment transport and channel adjustments associated with dam removal: Field observations
Water Resources Research, 2007
1] This study documents changes in channel geometry, bed level profile, and bed grain size distribution and their relations with the sediment transport at the reach scale, following the removal of a low-head dam. After the removal, net sediment deposition occurred downstream of the dam, and net erosion occurred in the reservoir, but approximately less than 1% of the sediment stored in the reservoir was transported downstream. No bank erosion was evident either upstream or downstream of the dam. Bed deposition and scouring in the reservoir accounted for a decrease in the bed slope of 30%. The stations downstream of the dam had surface bed material sizes at least 40% finer than preremoval conditions. However, the sediment transport rates downstream of the dam were not significantly different from predam to postdam removal or from an upstream control. Overall, the removal of the dam had only minor effects on the channel adjustment downstream of the dam. A simple analysis linking transport to channel geometry explains this effect.
Revisiting the homogenization of dammed rivers in the Southeastern US.
s u m m a r y For some time, ecologists have attempted to make generalizations concerning how disturbances influence natural ecosystems, especially river systems. The existing literature suggests that dams homogenize the hydrologic variability of rivers. However, this might insinuate that dams affect river systems similarly despite a large gradient in natural hydrologic character. In order to evaluate patterns in dam-regulated hydrology and associated ecological relationships, a broad framework is needed. Flow classes, or groups of streams that share similar hydrology, may provide a framework to evaluate the relative effects of dam regulation on natural flow dynamics. The purpose of this study was to use a regional flow classification as the foundation for evaluating patterns of hydrologic alteration due to dams and to determine if the response of rivers to regulation was specific to different flow classes. We used the US Geological Survey (USGS) database to access discharge information for 284 unregulated and 117 regulated gage records. For each record, we calculated 44 hydrologic statistics, including the Indicators of Hydrologic Alteration. We used a sub-regional flow classification for eight states as a way to stratify unregulated and regulated streams into comparable units. In general, our results showed that dam regulation generally had stronger effects on hydrologic indices than other disturbances when models were stratified by flow class; however, the effects of urbanization, withdrawals, and fragmentation, at times, were comparable or exceeded the effects of dam regulation. In agreement with the existing literature, maximum flows, flow variability, and rise rates were lower whereas minimum flows and reversals were higher in dam regulated streams. However, the response of monthly and seasonal flows, flow predictability, and baseflows were variable depending on flow class membership. Principal components analysis showed that regulated streams occupied a larger multivariate space than unregulated streams, which suggests that dams may not homogenize all river systems, but may move them outside the bounds of normal river function. Ultimately, our results suggest that flow classes provide a suitable framework to generalize patterns in hydrologic alterations due to dam regulation.
Case Study: Channel Stability of the Missouri River, Eastern Montana
Journal of Hydraulic Engineering, 2002
The construction of Fort Peck Dam in the 1930s on the Missouri River, eastern Montana, initiated a series of changes in hydrologic conditions and channel morphology downstream from the dam that impacted channel stability. Impacts included streambed degradation of up to 3.6 m and substantially altered magnitude, frequency, and temporal distribution of flows. To investigate the effects of the altered flow regime and bed degradation on bank stability, two independent bank-stability analyses ͑one for planar failures, the other for rotational failures͒ were performed on 17 outside meanders. Both included the effects of matric suction and positive pore-water pressures, confining pressures, and layering. Instability occurred from the loss of matric suction and the generation of positive pore-water pressures. In this semiarid region, such hydrologic conditions are most likely to occur from the maintenance of moderate and high flows ͑greater than 425-566 m 3 /s͒ for extended periods ͑5-10 days or more͒, thereby providing a mechanism for saturation of the streambank. For the postdam period, average annual frequencies of flows maintained above 566 m 3 /s for 5-and 10-day durations are 149 and 257% greater, respectively. The analyses indicated that 30% of the sites were susceptible to planar failures while 53% of the sites were susceptible to rotational failures under sustained moderate-and high-flow conditions, while under a worst-case rapid drawdown scenario, 80% of the banks were susceptible to failure. Despite the negative effects of the altered flow regime, analysis of maps and aerial photographs shows that closure of Fort Peck Dam has resulted in a fourfold reduction of the average rate of long-term channel migration between the dam and the North Dakota border.