Placing global stream flow variability in geographic and geomorphic contexts
Tóm tắt
The importance of hydrologic variability in sustaining natural riverine ecosystems is now well accepted. Over the last 15 years or so, many typologies and assessment tools have been developed to assist ecologists and managers in describing natural flow regimes in quantitative terms. In the course of this recent progress, however, some critical questions have arisen concerning the degree to which generalizations about flow regime characteristics are geographically dependent both within and among regions, and the degree to which flow variability alone captures critical environmental variability. In this paper we address these issues in a hierarchical framework that allows comparative statements about hydrologic variability to be made a multiple spatial scales, from local to global.
First, we examined hydrologic variability among 463 readily available daily streamflow gauges from five continents/countries around the world: Australia, New Zealand, South Africa, Europe, and the United States. Using ordination and clustering techniques, we identified similarities and differences among these gauges. We found that the US gauges exhibited the greatest overall flow variability among a suite of 66 hydrologic indicators, whereas Australian streams showed the greatest influence by interannual variability in flow. Similarities in overall flow regime were greatest between Australia and the US, whereas New Zealand streams were most regionally distinctive. These results support the idea of intercontinental distinction in streamflow variability at a global scale; however, they also point to important similarities in flow characteristics among continents/countries.
Second, within the continental United States, we examined how hydrologic variability changes along river profiles as catchment area increases for five river basins arrayed across a gradient of hydroclimatic variation. Using historical streamflow records that precede river impoundment, we found that small ‘headwater’ streams exhibit the greatest similarity in flow characteristics across the basins, as compared to mid‐sized and larger river reaches, which often diverged among the rivers. These results reveal the importance of more carefully defining the spatial domain of allowable hydrologic extrapolation from individual stream gauges and emphasize the need to stratify within basins when considering hydrologic variability at regional scales.
Third, we used a modeling approach to illustrate how geomorphic setting provides a context for assessing the ecological consequences of flow variation at the local scale of stream reaches. For modeled channels having the same sediment size distribution but with either entrenched or floodplain morphology, we found that the effective regime of bed movement for three hydrologically distinct streams depended as much on geomorphic setting as on flow regime
In sum, if riverine scientists wish to develop a general framework for comparing hydrologic variability across basins, regions, and continents, a hierarchical approach is advised. At very broad scales, intercontinental differences in flow regimes could allow a stratification of basins to identify similar hydroecological settings. Within continents or hydroclimatically similar regions, finer‐scale spatial analysis of flow regime types would further assist in hydrologic stratification, based only on the regionally‐relevant components of flow variability. Finally, within hydrologically homogeneous sub‐regions, geomorphic stratification could be applied to identify stream reaches or segments having similar hydrogeomorphic properties. Copyright © 2006 John Wiley & Sons, Ltd.
Từ khóa
Tài liệu tham khảo
Atabay S, 1999, River Sedimentation: Theory and Applications, 223
Breiman L, 1984, Classification and Regression Trees
Brown CB, 1950, Engineering Hydraulics
Dunne T, 1978, Water in Environmental Planning
EinsteinHA.1950.The bed‐load function for sediment transport on open channel flows. Technical Bulletin #1026 US Department of Agriculture Soil Conservation Service 71.
Growns J, 2002, Characterisation of Flow in Regulated and Unregulated Streams in Eastern Australia, 70
Hayden BP, 1988, Flood Geomorphology, 13
Hey RD, 1997, Applied Fluvial Geomorphology for River Engineering and Management, 223
Knighton AD, 1998, Fluvial Forms and Processes: A New Perspective
Lytle DA, 2004, Adaptations to natural flow regimes, Trends in Ecology and Evolution, 19, 97, 10.1016/j.tree.2003.10.002
Marion CB, 1964, Handbook of Hydrology
McMahonTA.1979.Hydrological characteristics of arid zones. The Hydrology of Areas of Low Precipitation No. 128. IAHS Canberra Australia;105–123.
McMahonTA.1982.World hydrology: does Australia fit?Proceedings of the Hydrology and Water Resources Symposium National Conferenence Publication 83/2 The Institution of Engineers;1–7.
McMahon TA, 1992, Global Runoff—Continental Comparisons of Annual Flows and Peak Discharges
Naiman RJ, 1995, The freshwater imperative: a research agenda
Poff NL, 2001, Scenarios of Future Biodiversity, 315
Sambrook‐Smith GH, 1995, The gravel‐sand transition along river channels, Journal of Sedimentary Research, 65, 423
Wharton G, 1995, Changing River Channels, 325