A Quantitative Framework to Derive Robust Characterization of Hydrological Gradients

If ecological management of river ecosystems is to keep pace with increasing pressure to abstract, divert and dam, we must develop general flow–ecology relationships to predict the impacts of these hydrologic alterations. Regional flow gradient analyses are a promising tool to quickly reveal these functional relationships, but there are considerable uncertainties in this method because of variability in the historical extent of flow data across different rivers, combined with multiple indices characterizing the ecological attributes of flow regimes. In response, we outline an objective framework for analysing spatial hydrologic gradients that addresses three major sources of uncertainty: robust estimation of flow indices, the potential for temporal trends to confound spatial variation in flow regimes and the statistical robustness to detect underlying hydrological gradients. The utility of our framework was examined in relation to flow regimes across multiple braided river catchments in Canterbury, New Zealand. We found that a subset of flow indices could be robustly estimated using only 10 years of flow data, although indices that captured flow ‘timing’ required longer time series. Temporal trends were unlikely to confound conclusions from a spatial hydrologic gradient analysis, and there were three statistically supported hydrologic gradients related to flow magnitude, flow variability and low flow events. The widespread application of robust spatial flow gradient analyses has the potential to further our understanding of how altered flow regimes affect the ecology of freshwater and riparian ecosystems, thereby providing the evidence base to inform river management. Copyright © 2016 John Wiley & Sons, Ltd.     

Classification of natural flow regimes in Poland

Hydrological classifications are aimed at simplifying spatiotemporal variability of flow regimes and, secondly, at supporting environmental flow management. The objective of this study was to perform classification of natural flow regimes in Poland using an inductive approach based on a set of hydrological metrics (HMs) and to develop a model for prediction of class membership based on a set of environmental variables (EVs). A set of 147 gauges with unmodified flow regimes was identified, and for each gauge, values of 73 HMs and 28 EVs were computed. Classification was performed using k‐means and k‐medoids techniques, based on 4 principal components explaining 73.4% of variability in HMs. Out of 7 distinguished classes, 4 (P1–P4) were spread across the Polish Plain, 1 (U5) was restricted to uplands, and 2 (M6 and M7) to mountains. The between‐class differences in HMs and EVs were generally high, although classes P1 and P3 were not easily distinguishable. Mean predictive accuracy of the developed random forest model was 79%, which is high compared to other studies of this type. The lowest accuracies (0 and 50%) were achieved by 2 classes with the lowest counts. Variables representing diverse aspects: hydrography, climate, topography, and geology had the highest importance in the random forest model. Future research can benefit from the database of selected gauges with computed HMs, EVs, and assigned classes, freely available through a long‐lasting data repository. With this study, the first step towards application of the ELOHA framework for environmental flow management at regional scale has been achieved.     

Determining the effects of dams on subdaily variation in river flows at a whole‐basin scale

River regulation can alter the frequency and magnitude of subdaily flow variations causing major impacts on ecological structure and function. We developed an approach to quantify subdaily flow variation for multiple sites across a large watershed to assess the potential impacts of different dam operations (flood control, run‐of‐river hydropower and peaking hydropower) on natural communities. We used hourly flow data over a 9‐year period from 30 stream gages throughout the Connecticut River basin to calculate four metrics of subdaily flow variation and to compare sites downstream of dams with unregulated sites. Our objectives were to (1) determine the temporal scale of data needed to characterize subdaily variability; (2) compare the frequency of days with high subdaily flow variation downstream of dams and unregulated sites; (3) analyse the magnitude of subdaily variation at all sites and (4) identify individual sites that had subdaily variation significantly higher than unregulated locations. We found that estimates of flow variability based on daily mean flow data were not sufficient to characterize subdaily flow patterns. Alteration of subdaily flows was evident in the number of days natural ranges of variability were exceeded, rather than in the magnitude of subdaily variation, suggesting that all rivers may exhibit highly variable subdaily flows, but altered rivers exhibit this variability more frequently. Peaking hydropower facilities had the most highly altered subdaily flows; however, we observed significantly altered ranges of subdaily variability downstream of some flood‐control and run‐of‐river hydropower dams. Our analysis can be used to identify situations where dam operating procedures could be modified to reduce the level of hydrologic alteration. Copyright © 2009 John Wiley & Sons, Ltd.     

Assessing the impact of human activities on hydrological and sediment changes (1953–2000) in nine major catchments of the Loess Plateau,China

The Range of Variability Approach (RVA) is employed to investigate the variability and spatial patterns of hydrological and sediment changes (1953–2000) induced by intensified human activities, i.e. the implementation of water and soil conservation measures, in nine major catchments of the Loess Plateau, China. Results indicate that: (1) streamflow and sediment load regimes were greatly changed by the implementation of conservation measures; (2) similar spatial patterns of high hydrological and sediment changes resulting from the intensive implementation of conservation measures are observed in most catchments of the middle Yellow River. However, slightly different behaviours of changes exist due to the unique complexity of hydrological and sediment processes in this region and (3) the impacts of various conservation measures on hydrological and sediment processes are closely associated with the extent and types of these measures. Engineering works have a quite immediate impact on streamflow and sediment regimes. Considerable vegetation controls are recognized as additional important driving forces for high hydrological and sediment alterations among various soil conservation measures. In vegetation controls, afforestation is the major factor causing the changes of runoff and sediment processes in these nine catchments. The results of the current study will be greatly beneficial to the regional water resources management and restoration of eco‐environmental system in the middle Yellow River basin characterized by intensified soil‐conservation measures under the changing environment. Copyright © 2009 John Wiley & Sons, Ltd.