Hydrodynamic modelling study of a fish exclusion system for a river diversion

River diversions are often equipped with some device to exclude fish, such as fish screens. Flow pattern changes due to fish screen systems were investigated using a three‐dimensional numerical model solving the Reynolds‐averaged Navier‐Stokes (RANS) equations. A porous media obstacle, which is commonly used for ground water flow modelling, was employed to model a fish screen. Fish screens require a velocity component perpendicular to the screen (approach velocity), allowing for water diversion. Meanwhile, it is imperative that this velocity not result in pinning fish to the screen but allowing for fish to be guided to a different location. Thus the ratio of sweeping velocity to approach velocity (V_R) is an important criterion in fish screen design. 20:1 V_R and 10:1 V_R models were tested under high and low flow rates in this study. Screen head loss coefficients for various wire Reynolds numbers were compared with laboratory model measurements to verify the mathematical results. Two different screen types were simulated: perforated plate and wedged wire. Altering global porosity and local permeability of a porous obstacle results in flow direction changes that effectively simulate different screen materials in the numerical model. Model simulations of head loss coefficients and velocity ratios showed good agreement with the laboratory model measurements. The wedged wire allows for more control of the velocity ratio along the screen system than the perforated plate. Baffles installed behind each fish screen bay promote uniform flow distribution along the screen. The porous media obstacle assumption is shown to effectively simulate the hydraulics of various configurations of fish screens at river diversion channels. Copyright © 2010 John Wiley & Sons, Ltd.     

Development of shaft lines with a small number of bearings for high power steam turbines

A comparative analysis is made of designs for high power steam turbines with a small number of bearings and those with multiple bearings. Experimental data on the finishing of bearings are presented. The eigenmodes and forced oscillations of a shaft line are calculated and recommendations are made for improving the balancing quality. __________ Translated from élektricheskie Stantsii, No. 12, December 2007, pp. 52–58.     

Prioritizing removal of dams for passage of diadromous fishes on a major river system

Native diadromous fishes have been extirpated from much of the Susquehanna River system for nearly a century. Recent restoration efforts have focused on removal of dams, but there are hundreds of dams and presently there is no biologically based system to assist in prioritizing their removal. We present a new method that uses existing habitat suitability index models (HSI) for American shad Alosa sapidissima, alewife A. pseudoharengus, blueback herring A. aestivalis, and American eel Anguilla rostrata to prioritize the removal of non‐hydropower dams within the Susquehanna River system. We ranked HSI scores for each of the four species, association between a landscape‐scale factor and HSIs, length of river opened by removing a dam, and distance from the mouth at Chesapeake Bay for each dam and then calculated a mean rank prioritization for dam removal by averaging the ranks for the seven criteria. This prioritization method is resistant to outliers, is not strongly affected by somewhat arbitrary decisions on metrics included in the analysis, and provides a biologically based prioritization for dam removal that can be easily amended to include other metrics or adapted to other river systems and that complements other social and economic considerations that must be included in decisions to remove dams. Published in 2008 by John Wiley & Sons, Ltd.     

Declining phosphorus as a potential driver for the onset of Didymosphenia geminata mats in North American rivers

Didymosphenia geminata is a stalk‐forming diatom capable of creating thick benthic mats in low‐nutrient streams. There are two hypotheses to explain the rapid worldwide increase in occurrence of nuisance D. geminata mats: (a) Cells are spread among rivers and across broad ecoregions through natural and anthropogenic vectors, or (2) pre‐existing D. geminata populations are forming mats in response to changing environmental conditions within the habitat. Low phosphorus (P) concentrations are a major trigger for stalk production by D. geminata cells. Although the environmental change hypothesis is gaining support among researchers, long‐term data sets demonstrating declining P concentrations prior to reported mat formation have been essentially absent from the literature. Here, we present long‐term datasets for two case studies for which long‐term P and D. geminata data coincide: the Matapedia River in Eastern Canada and the Kootenai River below Libby Dam in Montana, United States. Both rivers had declining P levels over time. However, there was a 2‐ and 20‐year lag time, respectively, between mat development and reaching the previously proposed average 2 μg/L soluble reactive P threshold for development. Although the Matapedia River provides some support of the environmental change hypothesis, the Kootenai River data set suggests other environmental factors may play a role in mat development. The data presented do not rule out the environmental change hypothesis but do suggest there may be conditions in addition to low P that must be met for mats to form and the environmental change hypothesis can likely be refined to include more parameters to better understand and mitigate the influence of mats.     

Optimization of regimes for the feed of highly concentrated culm-anthracite coal dust for burning in a TPP-210A boiler

Results are presented for regime adjustment of feed systems for a TPP-210A boiler for the burning of highly concentrated culm-anthracite coal dust. As compared with nonoptimal regimes, optimal regimes of high-concentration-feed systems improve the economy of the boiler by 1.7% on average. __________ Translated from élektricheskie Stantsii, No. 3, March 2007, pp. 34–38.     

Measurement and quantification of a sedimentation budget for a reservoir with regular flushing

This paper provides a case study of successful removal of reservoir sediment by empty flushing. The main aim of this study was to determine: (i) sediment inflow to the Cachí reservoir; (ii) the pattern and rate of deposition in the reservoir; (iii) the erosion within the reservoir during flushing; and (iv) sediment outflow at a downstream hydrological station during flushing. The results are integrated as a sediment budget for the reservoir. The drainage basin of the Cachí reservoir in Costa Rica is 785 km². The sediment budget for the period between two flushings indicates a sediment inflow to the reservoir of c. 930 000 tonnes and a net accumulation of c. 133 000 tonnes, or 14.3% of the sediment inflow. The sediment throughflow was also c. 133 000 tonnes up to the erosion phase of the flushing, and the outflow during flushing including bed load was 663 000 tonnes, i.e. 71.4% of the sediment inflow. Thus, the flushing of the reservoir was highly effective in releasing sediment. The balance of the sediment budget makes it probable that the major components of the sediment budget are of the right order of magnitude. The main principle to obtain correct sediment loads by the rating‐curve technique was to collect sediment data from a large number of storm events at equal time intervals during rising and falling stages. This was achieved by turbidimeter recordings. Because of the wide scatter of data, sediment rating curves were developed on mean sediment loads in discharge classes to avoid the bias of log regressions. The trap efficiency and sediment throughflow were determined with Sundborg's physically based sedimentation model. The throughflow amounted to 20% of the suspended sediment inflow, which compares well with the empirical budget. The depositional pattern in the Cachí reservoir was surveyed with side‐scan sonar, repeated echo‐soundings, and by excavating pits in deposits when the reservoir was empty. Deposition occurred mainly in the old river channel, indicating that the major part of the sediment is transported by density currents. The volume of eroded material in the reservoir during scour valve release was estimated by echo‐soundings before and after the flushing. Dry bulk density of the reservoir deposits was determined by X‐ray radiographic and densitometric analysis. The radiographic analyses indicated a dry bulk density of 0.4 g cm⁻³ of the loose material in the thalweg, and 0.7 g cm⁻³ of the whole deposition depth on the terraces. Copyright © 2000 John Wiley & Sons, Ltd.     

Hydrologic thresholds for riparian forest conservation in a regulated large Mediterranean river

Most riparian trees are phreatophytic, water table‐dependent plants which broadly differ in their tolerance to drought and permanent flooding. In semi‐arid settings, as water is limiting, inundations may be regarded as inputs rather than stresses for the survival of phreatophytes. In this study, the mortality rates and abundances of Populus alba, P. nigra, Salix alba and local Tamarix spp. were examined in 43 plots with different hydrologic conditions distributed across the floodplain of a large semi‐arid and Mediterranean river, the Ebro River (Spain). The objectives were to determine hydrologic thresholds for the maintenance of declining populations of those species, while providing novel information on their phreatophytic nature, and to examine shifts in the species composition along hydrologic gradients. All species exhibited significant relationships between mortality rates and hydrologic variables (deepest water table—WT, flood duration—FD and flood frequency—FF). S. alba was found to be the species with lowest tolerance to drier conditions (hydrologic thresholds for maintaining a mortality rate <50%: WT > ?1.22 m; FD: out of observation range; FF > 5.4 events y^?1), followed by P. nigra (WT > ?2.18 m; FD > 11.1%; FF > 3.8 events y^?1), Tamarix spp. (WT > ?2.96 m; FD > 3.7%; FF > 2.5 events y^?1) and P. alba (WT > ?3.45 m; FD > 1.7%; FF > 2.0 events y^?1). Only a significant reduction in S. alba relative abundance was observed as conditions got drier. The results provided quantitative information useful to guide management plans for the protection of Mediterranean phreatophytic tree species from further degradation and suggested that eventual natural or regulation‐induced droughts and groundwater declines would accelerate the loss of all phreatophytic species, especially S. alba. Copyright © 2010 John Wiley & Sons, Ltd.     

An assessment of the effectiveness of a vertical‐slot fishway for non‐salmonid fish at a tidal barrier on a large tropical/subtropical river

Fishways for salmon in temperate rivers have often been successful, but salmonid‐type fishways for non‐salmonid species in tropical and subtropical rivers have frequently failed. This study assessed the effectiveness of modifying a salmonid‐type pool‐and‐weir fishway into a vertical‐slot design on a tidal barrage on the subtropical Fitzroy River, in Queensland, north‐eastern Australia. In 38 paired samples of the top and bottom of the fishway, over 16 months, 29 fish species and over 23 000 fish were collected at a maximum rate of 3400 per day. This study shows much greater potential for success with a vertical‐slot fishway as relatively few fish negotiated the original pool‐and‐weir design. Common species using the vertical‐slot fishway included blue‐catfish (Arius graeffei [Ariidae]), bony herring (Nematalosa erebi [Clupeidae]), striped mullet (Mugil cephalus [Mugilidae]), barramundi (Lates calcarifer [Centropomidae]), and long‐finned eels (Anguilla reinhardtii [Anguillidae]). Freshwater shrimp (Macrobrachium australiense [Palaemonidae]), juvenile crabs (Varuna litterata [Grapsidae]) and long‐finned elvers did not ascend the full length of the fishway and specific fishways for these species are recommended. Fish between 25 and 640 mm in length ascended the fishway, although the passage of smaller size classes of immature fish was restricted and this may be important for the sustainability of these migratory populations. The barramundi (200–640 mm) which ascended the fishway were all immature fish. However, during a period of low river flows enlarging the width of the vertical‐slot from 0.15 to 0.45 m only encouraged a small number of larger fish (890 mm maximum length) to enter. The strong diel movement patterns of many species will need to be considered in future fishway design. Blue‐catfish could ascend the fishway in 2 h, but many fish remained in the fishway and this behaviour may cause crowding and a reduction in fishway capacity. Further work is needed to assess the proportion of fish finding the fishway entrance. However, the findings suggest that vertical‐slot fishways with lower water velocities and turbulence than salmonid fishways have great potential to pass the diverse migratory fish fauna of subtropical and tropical rivers. Copyright © 1999 John Wiley & Sons, Ltd.     

Upply unit of a fishpass for low-head hydro developments

Onclusions  Thus, the investigations established that the vertical gate with a dentate lower edge can be used as the supply uni sh locks; in this case its characteristics are not inferior to sluice gates installed on operating fishways. It was found that: discharge with free access of air under the nappe beyond the gate with the dentate lower edge is observed if the r (ltth+a)/h_lp<1.45. In the case of discharge without free access of air a roller is formed, the length of which depends the ratio given above; the discharge coefficient μ increases with increase ofa/h_lp; an expression was obtained which can be used to determine the length of the stretch of increased nonuniformity of elocity distribution over the cross section of the flow in the fish-holding flume; a dependence of the change in turbulence intensity beyond the gate with the dentate lower edge was obtained; turbulence intensity behind the gate with the dentate lower edge is lower than behind the vertical gate. Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 4, pp. 33–35, April, 1997.     

A water policy intercomparison model for a region with three seasons

A water policy model is proposed as a solution to the problem of obtaining maximum net benefit from providing irrigation and urban water in regions where the major source of supply is groundwater. In essence, the model introduces an innovative scheme based on two types of penalties. These intervene when either watertable elevation falls below a critical value during the operation of a system of wells or a remote source is used to partially cover the needed amount of water expected from the basic groundwater source. Another specific idea of the model is the consideration, for southern regions, of a three-season division in the climatic character of a year. The algorithm is illustrated by a numerical example in which five possible alternatives are compared. The conclusion of the study (although a function of regional economics, natural conditions, as well as specific zonal water policy constraints) reveals a compromise between limiting the amount provided from remote sources and confining the aquifer operation to critical values of the water-table elevation.Notation B benefits from water use, 10³ US$ - C sum of total costs, 10³ US$ - CMR total maintenance-repair cost, 10³ US$ - CO total cost of operation, 10³ US$ - C _HO unit cost of operation per hour, US$ hr^–1 - C _y unit average cost of a repaired pump, US$/(year × well) - d screen diameter for each well, m - H _G average groundwater elevation, m - H _{W cr} critical water elevation value in wells, m - H _{W dj} hydraulic head deficit in wells (belowH _{W cr} ), m - H _{W j} seasonal water elevation in each well, m - j current season - K average hydraulic conductivity of the aquifer, m s^–1 - NB net benefit, 10³ US$ - Ns maximum number of seasons - N _HO number of hours of operation per well and month - N _{W j} number of wells in operation over a seasonj - n _j number of months over each seasonj - P sum of total penalties, 10³ US$ - PH total penalty for pumping whenH _{W dj} >0, 10³ US$ - PQ total penalty for remote source use, 10³ US$ - P _RSj unit penalty for remote source use, 10³ US$ month^–1 - P _{W dj} unit penalty for pumping whenH _{W dj} >0, 10³ US$ month^–1 - pRM percentage of repaired and maintained pumps yearly, % - Q _iRj discharge needed for irrigation use, m³ s^–1 - Q _Nj total discharge needed by users, m³ s^–1 - Q _Pj total seasonal yield capacity of the battery, m³ s^–1 - Q _RSj discharge covered from remote sources, m³ s^–1 - Q _UWj discharge needed for urban water use, m³ s^–1 - Q _j seasonal operated pumping rate in each well, m³ s^–1 - Q _waj weighted average of pumping rate at timet _j , m³ s^–1 - S _Y average specific yield of the aquifer - S _cr critical drawdown value in wells, m - S _j seasonal drawdown in each well - T average transmissivity of the aquifer, m² s^–1 - t _OPj current duration of system operation - t _j –t _j–1 duration of each seasonj     

Development of 3-D Optimal Surface for Operation Policies of a Multireservoir in Fuzzy Environment Using Genetic Algorithm for River Basin Development and Management

A Multi objective, Multireservoir operation model for maximization of irrigation releases and maximization of hydropower production is proposed using Genetic Algorithm. These objectives are fuzzified and are simultaneously maximized by defining and then maximizing level of satisfaction (λ). In the present study a multireservoir system in Godavari River sub basin in Maharashtra State, India is considered. Problem is formulated with four reservoirs and a barrage. A monthly Multi Objective Genetic Algorithm Fuzzy Optimization (MOGAFUOPT) model for the present study is developed in ‘C’ Language. The optimal operation policy for maximization of irrigation releases, maximization of hydropower production and maximization of level of satisfaction is presented for existing demand in command area. The entire range of optimal operation policies, for different levels of satisfaction i.e. λ (ranging from 0 to 1), are determined. From the relationships developed amongst irrigation releases, hydropower production and level of satisfaction, a three dimensional (3-D) surface covering the whole range of policies has been developed. This solution surface can be the basis for decision makers for implementing the policies. Considering the future requirements in the command area, both the irrigation and hydropower demands are increased by 10 and 20%. The optimal operation policy for maximization of irrigation releases, maximization of hydropower production and maximization of level of satisfaction is also presented for these cases. The 3-D solution surface is also developed in these cases.     

An analytical solution for water-table fluctuation in a finite aquifer due to transient recharge from a strip basin

Two cases of water-table fluctuation in a finite aquifer in response to transient recharge from a strip basin are investigated. In the first case the aquifer is bounded by open water-bodies, whereas in second one the aquifer is bounded by impermeable boundaries on both sides. Analytical solutions are presented to predict the transient position of the water-table. The solutions are obtained by using finite Fourier sine and cosine transforms.Notations A width of the aquifer [L] - e specific yield - h variable water-table height [L] - h ₀ initial water-table height [L] - weighted mean of the depth of saturation [L] - K hydraulic conductivity [LT^–1] - m,n integers - P ₁ +P ₀ initial rate of transient recharge [LT^–1] - P ₁ final rate of transient recharge [LT^–1] - P constant rate of recharge [LT^–1] - x ₁ distance of left boundary of the strip basin [L] - x ₂ distance of right boundary of the strip basin [L] - t time of observation [T] - decay constant [T^–1]     

Green hydropower: a new assessment procedure for river management

Hydropower is the most important renewable electricity source worldwide. It shows clear advantages for the global CO₂ balance but creates serious ecological impacts on a local scale. As a consequence, concern for the conservation of natural river ecosystems is growing within society and more people are willing to pay extra for so‐called ‘green electricity’. The definition of ‘green’, however, is not straightforward and customers cannot directly examine the quality of electricity products. Therefore, credible certification of high ecological standards is essential for successful green electricity marketing. In this paper we introduce a new assessment procedure for evaluating environmentally compatible hydropower production. This so‐called ‘Green Hydro’ concept was developed in the context of a multidisciplinary case study on a 400 MW hydropower scheme in the Southern Alps of Switzerland. The concept guarantees both general standards for different schemes operating in different types of watersheds and flexibility for local particularities. We developed an environmental management matrix that considers basic criteria and eco‐investments and covers five environmental areas of concern (i.e. hydrological character, connectivity, morphology, landscape, and biological communities). The ecological perspective is complemented by five management domains (i.e. instream flow regimes, hydropeaking, reservoir and bedload management, and power plant structures). Applying assessment and modelling tools for the Green Hydro procedure showed that dynamic habitat models allowed quantification of the effects of different instream flow regulations at morphologically distinct sites. In this case, morphological restoration could be more beneficial than increasing the minimum flow. The first experience with the Green Hydro certification is encouraging. So far, 13 facilities have successfully passed the certification procedure. They produce a total of 186 GWh green electricity per year, which is sufficient for the supply of almost 40 000 households in Switzerland. Copyright © 2004 John Wiley & Sons, Ltd.     

Shallow and deep water aquatic vegetation potential for a midlatitude pool of the Upper Mississippi River System with drawdown

Prior to navigation dam and levee placement, the Upper Mississippi River (UMR) flowed through a wide floodplain supporting a diverse ecosystem. Diversity was created by variable flood frequencies and water flow, but presently high and static water levels supporting river navigation have caused low diversity of aquatic vegetation in locations within the UMR. A pool‐scale water level drawdown was proposed as a wetland management tool to mimic historic low water flow for UMR Navigation Pool 18, between Oquawka and Keithsburg, IL. The objectives of this research are to determine plant species, density, and diversity expected for a drawdown in Pool 18. A seedbank and propagule assay was used to evaluate drawdown plant species response. Emergence was tested using river bottom substrate samples collected in 2009 from the proposed drawdown area. Samples were treated at two hydrologic levels: shallow (3‐cm depth) and deep (16‐cm depth). Dominant species in the shallow flooded treatment were Gratiola neglecta, Leersia oryzoides, Eleocharis palustris, Sagittaria latifolia, and Ammania coccinea. Deep flooded dominant taxa included G. neglecta, S. latifolia, Vallisneria americana, and A. coccinea. Each treatment indicated a seedbank of moderate diversity with a shallow treatment diversity of D = 0.56 and deep treatment diversity of D = 0.44. Plant density for the shallow flooded treatment was 213 stems/m² (±112; 95% CI), and deep flooded hydrologic treatment, 206 stems/m² (±82; 95% CI). It is expected that this drawdown will provide an intermediate ecological disturbance resulting in greater species diversity and density currently lacking in this portion of the Upper Mississippi River System.     

Analytical solutions of unsteady drainage problems for soils subjected to variable recharge from a semi-confined aquifer

In drainage of agricultural lands, the upward vertical recharge from a semi-confined aquifer depends on the difference of the piezometric heads on the two sides of the semi-impermeable layer through which this recharge takes place. This means that the recharge through the semi-impermeable base depends on the unknown height of the unsteady water table. In the nonhomogeneous Boussinesq equation, which describes the drainage problems, the downward uniform rate of the recharge from rain or irrigation and the recharge from the semiconfined aquifer are expressed by two terms. By solving the Boussinesq equation expressions for the nondimensional height of the water table and the nondimensional discharge of the drains per unit drained area are obtained for three different initial conditions. Some known solutions are shown as special cases of the present solutions. Variation of nondimensional water table heights at half distance of the drain spacing and the nondimensional discharge of the drains with nondimensional time have been graphically illustrated with the help of synthetic examples.Notation B _s thickness of the semi-impervious layer [L] - c hydraulic resistance of the semi-impervious layer [T] - D depth of the drains from the base [L] - d _e equivalent depth [L] - h=h(x, t) height of the water table [L] - h ₀ initial height of the water table [L] - h _t water table height at mid-distance of drains att [L] - h _j ,h _k water table height at mid-distance of drains at timej andfk, respectively [L] - H ₀ piezometric head in the semi-confined aquifer [L] - K hydraulic conductivity of the soil [LT^–1] - K _s hydraulic conductivity of the semi-impervious layer [LT^–1] - k ₀,k ₁,k ₂ nondimensional constants - L distance between the drains [L] - q ₀ upward recharge per unit surface area through the semi-impervious layer [LT^–1] - q _t discharge per unit drainable area of drains at timet [LT^–1] - R,R ₀ recharge per unit surface area from rain or irrigation during the unsteady and steady-state, respectively, [LT^–1] - S specific yield of the soil - t time of observation [T] - x distance measured from the drain [L] - leakage factor [L] - nondimensional distance - nondimensional time     

Partial dam removal restores passage for a threatened salmonid

Dams represent one of the major forms of river alteration. As these structures reach the end of their lifespan, they often require extensive refurbishments or removal. A small‐scale water supply dam in Banff National Park (Alberta, Canada) was partially removed, creating a breach that allowed water to scour a new passage resembling a nature‐like fishway. We investigated the permeability of the partially removed dam as a means of validating the conservation benefits of the partial dam removal. We quantified the proportion of bull trout (Salvelinus confluentus), a threatened species in Canada, that approached and passed the fishway using radio telemetry receiver stations. The proportion of bull trout that approached the fishway was low (37.0%; N = 27 of 73), but was consistent with upstream reference sites (33%; N = 20 of 60). For those that did approach, the proportion of bull trout that passed yielded a high passage efficiency (77.8%; N = 21 of 27 that approached). The probability that a fish passed the fishway was related to water depth and time of day. Bull trout were more likely to pass when water depths were high (>0.40 m), and at night. Passage duration ranged from 5‐mins to 13‐days, suggesting that this resident species used the fishway for a variety of purposes (e.g., station holding and foraging) and not just transiting. Some individuals underwent large‐scale movements 2‐km upstream (15.1%; N = 11 of 73), or 2‐km downstream (2.7%; N = 2 of 73) following a successful passage event. This study provides new insight on how, in some instances, a breach in a dam can function as a nature‐like fishway, accommodating year‐round stream flows and providing hydraulic conditions suitable for fish passage without costly engineering or construction.     

Proposals for inhibiting abundant phytoplankton growth at the head of a river reservoir

In a river reservoir, the Ishitegawa Dam Reservoir in Japan, sites of abundant phytoplankton growth were investigated in connection with the water movement in the reservoir from January 1982 to January 1984 by comparing the distributions of chlorophyll a, water temperature, and coliform bacteria (Project A). The results distinguished three types of phytoplankton growth, of which one type, the abundant surface growth at the head of the reservoir, was most frequently observed. This case was considered to be caused by mixing of the surface lake water with the inflowing nutrient-rich river water at the shallow lake-head. Subsequently the effects of dissolved calcium and magnesium on the chlorophyll a and phytoplanktonic particulate phosphorus concentrations at the head of the reservoir were investigated until December 1987 (Project B). A trophic index, named the Ca-Mg index, was found which correlated positively with the chlorophyll a and phytoplanktonic particulate phosphorus concentrations in a logarithmic scale and varied in relation to the changes in the same index of the inflowing river water. Based on the ecological results of these two projects, two proposals are presented for inhibiting abundant phytoplankton growth at the head of a river reservoir. Proposal A: make the head deep and, in addition, create a strong near-bottom underflow of the inflowing river water. Proposal B: make a bypass in order to cut off the inflow of river water in the case of a high Ca-Mg index.     

A method for assessing channelization effects on riparian vegetation in a Mediterranean environment

This paper proposes a methodology to assess the effects of artificial embankments on riparian vegetation. It then tests the methodology on a mountain torrent system in Calabria, Southern Italy. The method delimits homogeneous reaches within which a sample of embanked and control (unembanked) sites is identified for study. Transects, subdivided into sample areas, are located in embanked and control sub‐reaches. At these transects, vegetation parameters (number of species, canopy cover of each species and vegetation layer, height of each vegetation layer, vegetation type, biological forms and ecological groups) are surveyed. Two new parameters (global canopy cover and weighted canopy height) are also proposed to give synthetic information on the global development of vegetation. A simple hydraulic index (cA^b/W) is used to explore differences in riparian vegetation both along the river and according to local narrowing caused by embanking. Application of this methodology to a torrent system (locally called ‘fiumara’) illustrates a clear influence of concrete embankments in the upper and middle torrent reaches. It demonstrates that torrent narrowing induces: a decrease in the number of vegetation types with a tendency to confine the types to generally lower evolution levels and with a less marked trend between the thalweg and embankment; an increase in annual species and decrease in perennial species; and also a lower global canopy cover with, sometimes, a reduction in the weighted canopy height (WCH). This example illustrates that the methodology provides useful information concerning the impact of existing control works, which can aid the design of new works and can inform environmentally sensitive restoration of Mediterranean water courses. Copyright © 2007 John Wiley & Sons, Ltd.     

Dimensionless volatilization rate for two pesticides in a lake

In recent years, toxic pollution has become a relevant topic in lake management, especially in developed countries. Consequently, great effort has been made to increase our knowledge of contaminant transport and transformation phenomena, and their effects on lake water quality. The present paper reports on the characterization of input parameters for a dimensionless steady‐state model that simulates fate processes of volatile environmental contaminants. Dimensionless volatilization rates for two pesticides, 2,3,7,8‐ tetrachlorodibenzo‐p‐dioxin (TCDD) and endrin aldehyde, in particular, are estimated using field data from almost 80 Italian lakes. Careful analyses of the results allow us to define the variation range of input parameters and introduce some simplifications into the complete solutions of the model.     

Effects of stream flow patterns on riparian vegetation of a semiarid river: Implications for a changing climate

As global climate change affects recharge and runoff processes, stream flow regimes are being altered. In the American Southwest, increasing aridity is predicted to cause declines in stream base flows and water tables. Another potential outcome of climate change is increased flood intensity. Changes in these stream flow conditions may independently affect vegetation or may have synergistic effects. Our goal was to extrapolate vegetation response to climate‐linked stream flow changes, by taking advantage of the spatial variation in flow conditions over a 200 km length of the San Pedro River (Arizona). Riparian vegetation traits were contrasted between sites differing in low‐flow hydrology (degree of stream intermittency) and flood intensity (stream power of the 10‐year recurrence flood). Field data indicate that increased stream intermittency would cause the floodplain plant community to shift from hydric pioneer trees and shrubs (Populus, Salix, Baccharis) towards mesic species (Tamarix). This shift in functional type would produce changes in vegetation structure, with reduced canopy cover and shorter canopies at drier sites. Among herbaceous species, annuals would increase while perennials would decrease. If flood intensities increased, there would be shifts towards younger tree age, expansion of xeric pioneer shrubs (in response to flood‐linked edaphic changes), and replacement of herbaceous perennials by annuals. Woody stem density would increase and basal area would decrease, reflecting shifts towards younger forests. Some effects would be compounded: Annuals were most prevalent, and tree canopies shortest, at sites that were dry and intensely flooded. Vegetational changes would feedback onto hydrologic and geomorphic processes, of importance for modeling. Increased flood intensity would have positive feedback on disturbance processes, by shifting plant communities towards species with less ability to stabilize sediments. Feedbacks between riparian vegetation and stream low‐flow changes would be homeostatic, with reduced evapotranspiration rates ameliorating declines in base flows arising from increased aridity. Copyright © 2009 John Wiley & Sons, Ltd.