Stream power

About: Stream power is a research topic. Over the lifetime, 1135 publications have been published within this topic receiving 51324 citations.

Modelling suspended sediment supply to the River Rhine drainage network: a methodological study.

Abstract: In the framework of a climate change research project, an approach and preliminary results are presented of modelling the suspended sediment supply to the drainage network of the River Rhine. Concepts of the GAMES model are used as a basis. In the model, the amount of mobilized sediment that actually reaches the stream network depends on the proximity of the sediment source to the stream, the occurrence of overland flow and on the character of the terrain along the route towards the channel (including surface roughness and slope angle). Attention is paid to problems that are specific to the large size of the studied basin and the spatial resolution of the available data set. Preliminary results show that estimates of sediment supply from hillslope to streams are reasonable. Calculated sediment supply was compared with measured sediment yields at several sampling stations in the Rhine basin. It appeared that suspended sediment supplied in lower parts of the basin is transported more effectively through the alluvial system. A large part of the sediment produced in the Alps and in the Swiss middle mountains is stored in the alluvial system further downstream where stream power decreases.

Stability analysis of gravel-bed rivers: comparison between natural rivers and disturbed rivers due to human activities

Abstract: The present research studies fluvial processes –water and sediment flows – that define the shape of an alluvial channel. The relationship between forms and processes is complex because they are interrelated: the channel shape influences the water flow which drives the sediments movement on the channel bed that modifies the channel form, closing a circle. Although, the objective of the work is a very old question in fluvial studies, to explain the shape of rivers in terms of external controls and internal processes, the problem has not been solved yet and this study provies new elements for its solution. The start of the quest for linking process and forms can be found in the development of regime theories which consists of a set of equations to estimate the width, depth and slope of a stable channel if liquid discharge and sediment supply are known. Regime theories were created in the XIX century within the context of hydraulic engineering in order to design stable irrigation canals (e.g. Kennedy, 1895; Lacey, 1930; Lane, 1955). Leopold and Maddock (1953) introduced the quantitative concept of hydraulic geometry into the context of fluvial geomorphology and showed that alluvial rivers adjust both their slope and channel in order to be in equilibrium for a certain representative discharge. The first studies were eminently empiric, hence there has also been an intense theoretical work focused on explaining regime relations. Parker (1978) demonstrated the importance of bank erodibility, and the need of using improved hydraulic models to calculate the shear stress distribution on irregular cross-sections. Alternative conceptual approaches have been used to explore geometrical channel properties. Langbein & Leopold (1962) took advantage of thermodynamic principles to suggest that the distribution of energy in a river system tends towards the most probable state. After this first pioneering work, further so-called “extremal” hypotheses were proposed such as: minimum unit stream power (Yang and Song, 1979), minimum stream power (Chang, 1980), minimum energy dissipation rate (Brebner and Wilson, 1967; Yang et al., 1981), maximum sediment transport rate (White et al., 1982), maximum friction factor (Davies and Sutherland, 1983) and maximum resistance to flow (Eaton et al, 2004). Millar & Quick (1993) and Millar (2005) proposed models that take into account the bank strength, a distinctive condition not considered in previous works. Because of their lack of physical-based principles, extremal hypothesis approaches have been extensively criticized (Ferguson, 1986; Parker et al., 2007). Defenders claimed their validity based on the principle of least action (Nanson and Huang, 2008) or on the opposed feedback processes acting at the cross-section scale (Eaton et al., 2006). Regime models usually consider three degrees of freedom (width, depth, and slope) and four external control variables (liquid discharge, sediment supply, bed grain size, and bank strength). However, these variables reflect geomorphic processes acting at different temporal and spatial scales (Weichert et al. 2009) a crucial aspect not considered in regime models. The first part of the research was then dedicated to review and discuss theoretical issues inherent to the representation of fluvial systems and to regime theories. As a result, I proposed that a) physical laws and constrains describe the behaviour of a population of river reaches, instead of describing the exact processes within a single river reach; and b) each object contained in the population has uncertain boundaries (width, depth) and uncertain properties (median grain size, slope, bankfull discharge). Regime theories were classified according to the number of dimensions and the way of modeling the fluvial system. In this way, light was shed on the current debate about the validity of extremal hypothesis theories. The second part of the research focus on the study of the river-populations, consisting on the comparison of natural river reaches in Patagonia Region (Argentina) and river reaches disturbed due to human activities in Northern Italy. Extensive field measurements were conducted in Italy and Argentina; five river reaches were surveyed in Italy (belonging to Brenta, Piave and Cordevole rivers, in the Veneto Region) and ten river reaches in Argentina (in the mountain range of Central Patagonia). River reaches were chosen for their morphological homogeneity and for having at least 20 years of continuous flow record. In Argentina systematic measurements began by the middle of twentieth century. For the selected gauge stations records covered a time span ranging from 25 to 63 years. in Italy, water discharge has been measured at the Brenta River since 1924 at the Barzizza station and for the Piave River, flow records are derived from three gauging stations at Segusino, Belluno y Perarolo. Reaches were selected for being completely alluvial and having at least one bank free to evolve. In some cases a thick vegetation was growing in the banks, and in few cases one of the banks was protected with groynes. All selected reaches started and finish at riffles and extended along a whole wave length comprising three riffles and two pools. Then extensive and detailed field information was used to compare natural rivers in Patagonia and disturbed in Italy. The comparison was aimed to assess the stability state of Italian rivers, considering the properties of rivers in Patagonia as a reference of stable state. Then, following the concept of spatial scales and channel response proposed by Weichert et al. (2009), the consequences in regime models of considering the hypothesis that, while channel width and depth adjust quickly to changes in water and sediment supply, reach slope requires longer time spans, was explored. Three models, all of them incorporating a bank stability criterion, were considered in this study. In order to evaluate the performance of models introducing the slope as an independent variable, two modifications to previous models were proposed. The study also used published hydraulic geometry of gravel-bed rivers in other geographical regions (92 streams reaches) and laboratory data (36 small stream). Finally, Millar’s (2005) regime model was used to explain recent morphological changes and potential recovery in the Piave and Brenta rivers. The third and last part of the thesis was dedicated to the development and test of a 2D fully processes-based model, which was named LICAN-LEUFU. This part of the study was based on the assumption that “the channel morphology is driven by and is a consequence of within-channel processes; and a two-spatial-dimensions and depth-averaged model describes best the morphology of the channel”. The first part states that processes are the responsible of observed forms, which is the position hold in this study with regards to the debate on regime models. However, it should not be interpreted that extremal hypotheses are not necessary for predicting the channel shape. Extremal hypotheses express the behaviour at the reach scale while here, reach-scale features are explained by processes acting at a lower spatial scale. The second part means that the 2D model should do better in predicting channel morphology than 1D or aggregated models, i.e, the model is capable of predicting the reach-average form (width and depth) and also within channel morphology (pools and riffles) that are not within the capabilities of 1D or aggregated models. The model was tested in three different ways. The first test was based on flume measurements conducted at the facilities of the University of Hull. The model was used to predict the response of a laboratory flume that developed a static armour under conditions of sediment starvation. The observational consequences consisted on the bed change, surface grain size distribution change, outgoing sediment transport (bulk and grain size distribution). The second test was a middle-term simulation in which the model had to predict the shape of Azul River providing the actual water discharges, bed material, and estimated sediment supply, i.e., it was an application of the 2D model in the context of regime theories. The last test concerned the application of the model to a field case study: the Brenta River. The model was loaded with the initial morphology and surface grain size distribution and a series of runs were performed imposing the recorded discharges. Model predictions were compared against the final DTM (digital terrain model) and then used for assessing the possible evolution of the reach

Preliminary Study on Hydrodynamic Characteristics of Overland Flow and Sediment Yields of Gully Heads in Yuanmou Hot-dry Valley

Abstract: Runoff dynamic parameters,sediment contents and soil erosion amounts of gully heads were studied in Yuanmou dry-hot valley by situ scouring tests under different runoff fluxes.The results showed that:(1)Under different runoff flow condition,Reynolds numbers obtained in gully head drainage area and gully bed were both greater than 500,which indicated the state of runoff flow belonged to turbulence flow.Their Froude numbers were greater than 1,which indicated the runoff flow was torrent flow.Resistance coefficient(f) obtained from drainage area and gully bed both in gully 1(without inner cavities in gully wall) and gully 2(with inner cavities in gully wall) decreased with the increase of runoff flow.Runoff erosivity(runoff shear stress,stream power,unit stream power) increased when runoff flux increased.(2)In the same runoff conditions,sediment content and soil erosion amount of gully 1 were greater than those of gully 2,which indicated that in the same conditions,the forming stage of cavities was more active than its successive stage in sediment yielding.(3)A positive correlation was found between soil erosion amount and runoff energy loss,Reynolds numbers,Froude numbers,shear stress,stream power,unit stream power of gully heads,and a negative correlation was also found between soil erosion amount and the runoff resistance coefficient(f).