Christopher P. Konrad

Large-scale Flow Experiments for Managing River Systems

Experimental manipulations of streamflow have been used globally in recent decades to mitigate the impacts of dam operations on river systems. Rivers are challenging subjects for experimentation, because they are open systems that cannot be isolated from their social context. We identify principles to address the challenges of conducting effective large-scale flow experiments. Flow experiments have both scientific and social value when they help to resolve specific questions about the ecological action of flow with a clear nexus to water policies and decisions. Water managers must integrate new information into operating policies for large-scale experiments to be effective. Modeling and monitoring can be integrated with experiments to analyze long-term ecological responses. Experimental design should include spatially extensive observations and well-defined, repeated treatments. Large-scale flow manipulations are only a part of dam operations that affect river systems. Scientists can ensure that experimental manipulations continue to be a valuable approach for the scientifically based management of river systems.

Are large-scale flow experiments informing the science and management of freshwater ecosystems?

Greater scientific knowledge, changing societal values, and legislative mandates have emphasized the importance of implementing large-scale flow experiments (FEs) downstream of dams. We provide the first global assessment of FEs to evaluate their success in advancing science and informing management decisions. Systematic review of 113 FEs across 20 countries revealed that clear articulation of experimental objectives, while not universally practiced, was crucial for achieving management outcomes and changing dam-operating policies. Furthermore, changes to dam operations were three times less likely when FEs were conducted primarily for scientific purposes. Despite the recognized importance of riverine flow regimes, four-fifths of FEs involved only discrete flow events. Over three-quarters of FEs documented both abiotic and biotic outcomes, but only one-third examined multiple taxonomic responses, thus limiting how FE results can inform holistic dam management. Future FEs will present new opportunities to advance scientifically credible water policies.

Effects of urban development in the Puget Lowland, Washington, on interannual streamflow patterns: Consequences for channel form and streambed disturbance

fraction of time that streamflow exceeds the 0.5-year flood (T0.5). Urban streams had low interannual variability in annual maximum streamflow and brief duration of frequent high flows, as indicated by significant correlations between road density and both CVAMF and T0.5. The broader distribution of streamflow indicated by TQmean may be affected by urban development, but differences in TQmean between streams are also likely a result of other physiographic factors. The increase in the magnitude of frequent high flows due to urban development but not their cumulative duration has important consequences for channel form and bed stability in gravel bed streams because geomorphic equilibrium depends on moderate duration streamflow (e.g., exceeded 10% of the time). Streams with low values of TQmean and T0.5 are narrower than expected from hydraulic geometry. Dimensionless boundary shear stress (t*) for the 0.5-year flood was inversely related to T0.5 among the streams, indicating frequent and extensive bed disturbance in streams with low values of T0.5. Although stream channels expand and the size of bed material increases in response to urban streamflow patterns, these adjustments may be insufficient to reestablish the disturbance regime in urban streams because of the differential increase in the magnitude of frequent high flows causing disturbance relative to any changes in longer duration, moderate flows that establish a stable channel.

Partial entrainment of gravel bars during floods

[1] Spatial patterns of bed material entrainment by floods were documented at seven gravel bars using arrays of metal washers (bed tags) placed in the streambed. The observed patterns were used to test a general stochastic model that bed material entrainment is a spatially independent, random process where the probability of entrainment is uniform over a gravel bar and a function of the peak dimensionless shear stress t* of the flood. The fraction of tags missing from a gravel bar during a flood, or partial entrainment, had an approximately normal distribution with respect to t* 0 with a mean value (50% of the tags entrained) of 0.085 and standard deviation of 0.022 (root-mean-square error of 0.09). Variation in partial entrainment for a given t* demonstrated the effects of flow conditioning on bed strength, with lower values of partial entrainment after intermediate magnitude floods (0.065 < t* < 0.08) than after higher magnitude floods. Although the probability of bed material entrainment was approximately uniform over a gravel bar during individual floods and independent from flood to flood, regions of preferential stability and instability emerged at some bars over the course of a wet season. Deviations from spatially uniform and independent bed material entrainment were most pronounced for reaches with varied flow and in consecutive floods with small to intermediate magnitudes. INDEX TERMS: 1815 Hydrology: Erosion and sedimentation; 1821 Hydrology: Floods; 1869 Hydrology: Stochastic processes; KEYWORDS: sediment transport, bed material entrainment, disturbance, gravel bars, stochastic model

Channel Dynamics in the Middle Green River, Washington, from 1936 to 2002

Abstract Alluvial rivers are dynamic elements of the landscape in the Pacific Northwest. They expand, contract, and migrate across the bottom of valleys in response to changing flow and vegetation. Channel dynamics fundamentally structure river and floodplain ecosystems. Human activities that affect channel migration—including river regulation, channel revetments, and land use—have the potential for impacting river ecosystems. Active channel width and lateral movement of the active channel centerline was analyzed in 17 km valley segment of the middle Green River in western Washington from aerial photographs for 26 years of unregulated flows (1936–1961) and 41 years of flood regulation by Howard Hansen Dam. Area-based measures proved more robust for characterizing channel dynamics than cross-sectional measurements, though cross-sectional measurements are useful for resolving local processes. Prior to regulation from 1936 to 1961, the active channel width varied from 82 m to 120 m (median 94 m) and the channel migrated laterally a total of 68 m. After flood regulation from 1961 to 2002, the active channel width was generally smaller, varying from 84 m to 52 m (median 69 m) and the channel migrated 48 m. Streamflow greater than about 250 m3/s are most effective for forcing migration and have been reduced since dam construction. The river has re-occupied areas with increasing frequency since dam construction. High flows are essential to create new channel and floodplain habitats in the middle Green River, but land cover/use and revetments in the river corridor are also influential factors for maintaining channel dynamics.

Stream-temperature estimation from thermal infrared images

Stream temperature is an important water quality indicator. Spatial gradients of stream temperature can also be used to identify groundwater and surface water input locations in channel systems. Endangered fish populations are sensitive to elevated stream temperature, especially in the summer when low precipitation and high solar insolation increase temperatures beyond established thresholds. The removal of riparian vegetation and increases in surface run-off, that results from land-use change, also contribute to elevated stream temperatures. Thus, if critical watersheds are to be managed properly, accurate and spatially extensive temperature measurements are needed. For these purposes, it is necessary to know water surface temperature within 1/spl deg/C. Thermal infrared images (TIR) have long been used to estimate water surface temperatures, especially of the ocean where split-window techniques have been used to compensate for atmospheric effects. Streams are a more complex environment because 1) most are unresolved in typical thermal infrared images, and 2) stream corridors may consist of tall trees that irradiate the stream surface. Therefore, key additional problems to solve in measuring stream temperatures include both subpixel unmixing and multiple scattering. Over a watershed In the Cascade mountains of southern Washington, USA, we use fine-resolution airborne MODIS/ASTER Simulator (MASTER) data, and coarse-resolution ASTER data, to develop an approach for successful extraction of stream temperatures.

Classification of California streams using combined deductive and inductive approaches: Setting the foundation for analysis of hydrologic alteration

Regional classification of streams is an early step in the Ecological Limits of Hydrologic Alteration framework. Many stream classifications are based on an inductive approach using hydrologic data from minimally disturbed basins, but this approach may underrepresent streams from heavily disturbed basins or sparsely gaged arid regions. An alternative is a deductive approach, using watershed climate, land use, and geomorphology to classify streams, but this approach may miss important hydrological characteristics of streams. We classified all stream reaches in California using both approaches. First, we used Bayesian and hierarchical clustering to classify reaches according to watershed characteristics. Streams were clustered into seven classes according to elevation, sedimentary rock, and winter precipitation. Permutation-based analysis of variance and random forest analyses were used to determine which hydrologic variables best separate streams into their respective classes. Stream typology (i.e., the class that a stream reach is assigned to) is shaped mainly by patterns of high and mean flow behavior within the streams landscape context. Additionally, random forest was used to determine which hydrologic variables best separate minimally disturbed reference streams from non-reference streams in each of the seven classes. In contrast to stream typology, deviation from reference conditions is more difficult to detect and is largely defined by changes in low-flow variables, average daily flow, and duration of flow. Our combined deductive/inductive approach allows us to estimate flow under minimally disturbed conditions based on the deductive analysis and compare to measured flow based on the inductive analysis in order to estimate hydrologic change.

Analysis of low flows and selected methods for estimating low-flow characteristics at partial-record and ungaged stream sites in western Washington

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Effect of river confinement on depth and spatial extent of bed disturbance affecting salmon redds

ABSTRACT Human impacts on rivers threaten the natural function of riverine ecosystems. This paper assesses how channel confinement affects the scour depth and spatial extent of bed disturbance and discusses the implications of these results for salmon-redd disturbance in gravel-bedded rivers. Two-dimensional hydrodynamic models of relatively confined and unconfined reaches of the Cedar River in Washington State, USA, were constructed with surveyed bathymetry and available airborne lidar data then calibrated and verified with field observations of water-surface elevation and streamflow velocity. Simulations showed greater water depths and velocities in the confined reach and greater areas of low-velocity inundation in the unconfined reach at high flows. Data on previously published scour depth of bed disturbance during high flows were compared to simulated bed shear stress to construct a probabilistic logistic-regression model of bed disturbance, which was applied to spatial patterns of simulated bed shear stress to quantify the extent of likely bed disturbance to the burial depth of sockeye and Chinook salmon redds. The disturbance depth was not observed to differ between confined and unconfined reaches; however, results indicated the spatial extent of disturbance to a given depth in the confined reach was roughly twice as large as in the unconfined reach.

Visions, Objectives, Targets, and Goals

Establishing a shared and defined vision is a critical initial step in managing river resources and implementing environmental water regimes. We argue that the vision statement is best obtained through the stakeholder engagement processes and identification of ecosystem services, set within the context of wider constraints and national priorities, laws, and international commitments. This chapter discusses the approach to establishing objectives, targets, and goals that translate the social values espoused through the vision into scientific endpoints that support and inform management. We suggest a hierarchical ecosystem framework that establishes objectives, goals, and targets to account for different temporal and spatial scales of response.