Streamflow | EPFL Graph Search

Streamflow, or channel runoff, is the flow of water in streams and other channels, and is a major element of the water cycle. It is one runoff component, the movement of water from the land to waterbodies, the other component being surface runoff. Water flowing in channels comes from surface runoff from adjacent hillslopes, from groundwater flow out of the ground, and from water discharged from pipes. The discharge of water flowing in a channel is measured using stream gauges or can be estimated by the Manning equation. The record of flow over time is called a hydrograph. Flooding occurs when the volume of water exceeds the capacity of the channel. Role in the water cycle Streams play a critical role in the hydrologic cycle that is essential for all life on Earth. A diversity of biological species, from unicellular organisms to vertebrates, depend on flowing-water systems for their habitat and food resources. Rivers are major aquatic landscapes for all manners of plants and a

Hydrologic Drivers and Controls of Stream Ecological Processes

Serena Ceola

The temporal variability of streamflows is a key feature structuring and controlling ecological communities and ecosystem processes. The magnitude, frequency and predictability of streamflows, and thus of velocity and near-bed shear stress fields, control ecological structure and function, particularly of benthic organisms. River ecosystem dynamics is indeed deeply connected to streamflow variability, which chiefly relies on rainfall, climate, land use, and geomorphologic properties. Although alterations of streamflow regime due to climate change, habitat fragmentation or other anthropogenic factors are ubiquitous, their ecological implications remain poorly understood. The present Thesis therefore addresses a quantitative analysis of the implications of hydrological fluctuations on river ecosystems positing that they have major ecological importance. From a food-web perspective, the response of benthic biota to hydrologic change is analyzed through experimental and theoretical approaches. Starting from the theoretical characterization of the probability distribution function of streamflows, flow velocities, water depths and near-bed shear stresses at a site, where a comparison between measured and analytical streamflow statistics across several catchments is outlined, a flume experimental campaign has been carried out in order to analyze how flow variability affects biofilm growth and invertebrate grazing activity. Here, two contrasting flow regimes (a constant and a time-varying discharge sequence) and four different light conditions (from 90% to 27% of incoming light radiation), as a key control on biofilm algal productivity and grazer activity, have been performed. Average grazing rates were significantly enhanced under time-varying flow conditions and highest at intermediate light availability. This result suggests that the stochastic flow regime offers increased opportunities for grazing under more favorable shear stress conditions, with implications for stream ecology and trophic carbon transfer in stream food webs. A spatial generalization of the above results, upscaling them to whole river basins, is made possible by employing scaling relationships that are known to characterize the geometry and topology of natural landforms and riverine patterns. The proposed generalization accounts for hydrological characterizations of the driving streamflow variability where the explicit dependence of invertebrate suitability on geomorphic controls (e.g. river depth, bed shear stress and flow velocity) and on hydrologic conditions (e.g. embedded in the probability of streamflow, and the ensuing temporal correlations that define the persistence of the hydrologic signal in time) has been accounted for. Different invertebrate grazing species have been compared. Suitable dynamic models, describing benthic biota dynamics, in particular stream biofilm growth under both ungrazed and grazed conditions (that is, via the absence and presence of invertebrates, respectively), have been explored in order to assess the relevant processes that controlled biofilm-invertebrate temporal pattern. The present Thesis therefore aims to further our understanding of the linkages between hydrology and ecology, possibly leading to a comprehensive theory of hydrologic drivers and controls of biotic processes in stream benthic environments.

EPFL2012

Etude des processus hydrologiques par l'application du traçage environnemental

Abstract The main objective of this research is to improve the comprehension of the hydrological behaviour of natural catchments. This study is based essentially on the observation and the measurement of hydrological processes on the Haute-Mentue experimental research basin. The main originality of this work is to associate different types of measurements in order to obtain a better vision of hydrological processes responsible for streamflow generation. First the hydrological behaviour is studied at the catchment scale by the application of environmental tracing. Then hillslope measurements are conducted so as to identify the form of water flows through the catchment. Before the application of the environmental tracing technique on the Haute-Mentue, an uncertainty analysis of hydrograph separation models is proposed. In order to improve their interpretation in terms of hydrological processes, it is essential to estimate systematically their uncertainty. Two types of uncertainty are distinguished: the model uncertainty, which is affected by model assumptions, and the statistical uncertainty, which is due to the temporal variability of the chemical tracer concentrations of the components. The statistical uncertainty is studied using a Monte Carlo procedure. The model uncertainty is investigated by the comparison of alternative hypotheses concerning the chemical concentration of mixing model components and their spatio-temporal variability. This analysis validates in a way the use of hydrograph separation for the study of catchment hydrological behaviour. In fact it indicates that despite the uncertainty, the flow sources which generate the stream flow are clearly identified. However, the precision and the coherence of hydrograph separations can be improved by taking account of the temporal and spatial variability of component chemical concentrations. After this analysis, hydrographs recorded at the outlets of four Haute-Mentue sub-basins are separated by the application of a three-component mixing model based on the silica and calcium concentrations of water. This model allows the distinction of the following three components: direct precipitation, soil water and groundwater. The analysis of hydrograph separations of these four sub-basins allows the study of the spatial and temporal variability of hydrological responses. Concerning the spatial variability, despite the uncertainty of hydrograph separation, it appears that the hydrological behaviour of each sub-basin is different. The spatial variability of hydrological responses, which is observed essentially at the soil water contribution level, seems mainly due to the catchment morphology and geology. In general, soil contribution decreases with the steepness of the soil and the permeability of geological formation. As for the temporal variability of hydrological responses, it seems essentially to be controlled by the catchment humidity. Soil contribution increases with increasing basin humidity. A statistical analysis based on the development of multiple linear regressions allows the confirmation of the influence of these physico-climatic factors on the spatio-temporal variability of hydrological responses. In order to discover the processes responsible for the important soil water contributions highlighted by the application of environmental tracing, two experiments, one with a TDR system and the other with a rainfall simulator, were conducted within the catchment. On the whole, these two experiments indicate that the water flow processes are spatially quite heterogeneous and depend on very local properties. In fact, a geostatistical analysis of TDR measurements shows that the spatial variability of soil water content is very important at a local scale (1-20 meters). The soil infiltration capacity, determined by the simulation of artificial rainfall, is also spatially quite variable. This variability depends on the physical properties of the soil and geology but also on very local properties as macropores. After these different experiments, all of the observations done at the local scale as well as at the catchment scale are combined in order to get the maximum information about hydrological processes which are at the origin of streamflow. First, the TDR measurements partially confirm the environmental tracing results indicating that the soil water is an important potential source of subsurface flows. In view of the important spatial variability of soil water content and more particularly of the drainage dynamics, it seems that the stream flow generation is essentially controlled by processes at the local scale. The experiment with the rainfall simulator confirms this observation showing that the capacity of soil to transmit a water flow varies strongly in space. According to this experiment it seems, in the particular case of the Haute-Mentue, that soil water flows contributing to the stormflow generation moves essentially through the macropore system. In order to identify the form of subsurface flows and indirectly to confirm the role of macropores, an artificial tracing experiment was conducted. The transit speeds highlighted during this experiment are quick enough to conclude that the water contained in hillslopes contributes to the stromflow generation. Considering the physical and hydrodynamic properties of soils, only preferential flows can explain these transit speeds. In fact, from this experiment, it is not possible to know the nature of these preferential flows, but according to previous results it seems to be macropore flows. Finally, according to the information collected in this study, a conceptual model is proposed in order to explain the hydrological behaviour of the Haute-Mentue. This model, which is based essentially on the extension of contributing areas and on the role of preferential flows, allows to explain in terms of mechanisms the hydrological and chemical responses highlighted by hydrograph decompositions while respecting observations done at the local scale.

EPFL2000

Estimation of streamflow recession parameters: New insights from an analytic streamflow distribution model

Ana Clara Pereira Barbosa Santos, Andrea Rinaldo, Bettina Schaefli

Streamflow recession analysis characterizes the storage-outflow relationship in catchments. This relationship, which typically follows a power law, summarizes all catchment-scale subsurface hydrological processes and has long been known to be a key descriptor of the hydrologic response. In this paper, we tested a range of common recession analysis methods (RAMs) and propose the use of an analytic streamflow distribution model as an alternative method for recession parameter estimation and to objectively compare different RAMs. The used analytical model assumes power law recessions, in combination with a stochastic process for streamflow triggering rainfall events. This streamflow distribution model is used in the present framework to establish reference values for the recession parameters via maximum likelihood estimation. The model-based method has two main advantages: (a) joint estimation of both power law recession parameters (coefficient and exponent), which are known to be strongly correlated, and (b) parameter estimation based on all available streamflow data (no recession selection). The approach is applied to five rainfall-dominated catchments in Switzerland with 40 years of continuous streamflow observations. The results show that the estimated recession parameters are highly dependent on methodological choices and that some RAMs lead to biased estimates. The recession selection method is shown to be of prime importance for a reliable description of catchment-scale recession behaviour, in particular in presence of short streamflow records. The newly proposed model-based RAM yields robust results, which supports the further development of this method for comparative hydrology and opens new perspectives for understanding the recession behaviour of catchments.

2019