Showing papers in "River Research and Applications in 2005"

Fine-grained sediment in river systems : Environmental significance and management issues

Abstract: Fine-grained sediment is a natural and essential component of river systems and plays a major role in the hydrological, geomorphological and ecological functioning of rivers. In many areas of the world, the level of anthropogenic activity is such that fine-grained sediment fluxes have been, or are being, modified at a magnitude and rate that cause profound, and sometimes irreversible, changes in the way that river systems function. This paper examines how anthropogenic activity has caused significant changes in the quantity and quality of fine-grained sediment within river systems, using examples of: land use change in New Zealand; the effects of reservoir construction and management in different countries; the interaction between sediment dynamics and fish habitats in British Columbia, Canada; and the management of contaminated sediment in USA rivers. The paper also evaluates present programmes and initiatives for the management of fine sediment in river systems and suggests changes that are needed if management strategies are to be effective and sustainable. Copyright © 2005 John Wiley & Sons, Ltd.

A review of techniques available for delimiting the erodible river corridor: a sustainable approach to managing bank erosion

Abstract: Traditional policies for managing river bank erosion are currently being reconsidered as a result of increased awareness regarding the unsustainable nature of some forms of bank protection, and the role played by bank erosion in providing ecosystem services and supporting geomorphological functions. River managers are therefore increasingly seeking to preserve bank erosion within a defined erodible corridor. This paper provides an overview of the erodible corridor concept, focusing on the provision of guidelines for applying the concept in practice. We argue that a nested approach is required to address management objectives across a range of scales (network scale, reach scale, local scale) and review the different geomorphic tools that are available to help managers define the extent and inner sensitivity of the erodible corridor. These tools include simple rules of thumb such as evaluation of the equilibrium meander amplitude, historical approaches based on overlays of historical channel position, and simulation modelling. The advantages and limitations of each of these tools are discussed.

Linking scales of flow variability to lotic ecosystem structure and function

Abstract: Obtaining a better knowledge of how flow variability affects lotic biota is of considerable importance to stream and river management. We contend that processes at different hierarchical levels of organization in lotic ecosystems are sensitive to variation in flow at related hierarchical temporal scales. Ecosystem disturbance caused by large-scale events (i.e. infrequent, but high magnitude flow events with a recurrence interval of years to many days) tend to determine high-level characteristics of ecosystem structure (e.g. determining species pools, periphyton versus macrophyte dominance) and function (e.g. balance between auto- and heterotrophy). The high-level ecosystem characteristics then set the stage for processes that are influenced by flow variation that occurs at smaller temporal scale (i.e. minutes to milliseconds) such as colonization, biotic interactions and mass transfer enhancement of production. We contend that large-scale temporal events predominantly affect lotic ecosystems through physical drag processes ('drag-disturbance'), whereas small-scale flow variations affect ecosystems through mass-transfer processes (including invertebrate and fish food-uptake). Drag-disturbance and mass-transfer related processes mark the opposite ends of a continuum of flow variability controlled processes, with moderate temporal scale flow variability events affecting ecosystems through both drag-disturbance and mass-transfer processes in similar proportions. Flow variability, and associated effects on ecosystems, across these scales is discussed with reference to New Zealand rivers. We suggest that these concepts can be integrated across the full range of temporal scales based on a spectrum of velocity variations. This may provide a unifying conceptual model for how the structure and functioning of lotic ecosystems are linked to flow variability.

Sediment mining in alluvial channels: physical effects and management perspectives

Abstract: Based on a review of a number of documented case studies from various countries and a detailed analysis of sediment exploitation from five rivers in Italy and Poland, we discuss alluvial river response to extensive sediment mining. A sediment deficit caused by in-stream mining typically induces upstream- and downstream-progressing river incision, lateral channel instability and bed armouring. The resultant incision alters the frequency of floodplain inundation along the river courses, lowers valley-floor water tables and frequently leads to destruction of bridges and channelization structures. Mining also results in the loss or impoverishment of aquatic and riparian habitats. In the rivers of Italy and southern Poland studied, where mining coincided with other human activities that reduce sediment delivery to the channels, deep river downcutting, changes in channel pattern and, in one case, transformation from alluvial to bedrock boundary conditions were recorded over recent decades. The type and magnitude of channel response to sediment mining depend mainly on the ratio between extraction and sediment replenishment rates. The effects of mining will be especially severe and difficult to reverse: (i) where material is extracted at a rate greatly exceeding the replenishment rate; (ii) in single-thread rivers, that are generally associated with relatively low rates of catchment sediment supply; (iii) in channelized reaches; (iv) where rivers are underlain by a thin cover of alluvium over bedrock; and (v) where mining coincides with other human activities that reduce upstream sediment delivery. With a large number of detrimental effects of instream mining, the practice should be prohibited in most rivers except aggrading ones. Copyright © 2005 John Wiley & Sons, Ltd.

Hydrogeomorphic processes affecting riparian habitat within alluvial channel–floodplain river systems: a review for the temperate zone

Abstract: Hydrogeomorphic processes within alluvial river systems create, maintain and degrade riparian habitat. The dynamic interactions between water, sediment, aquatic-terrestrial landforms and biotic elements control the functional processes and biodiversity patterns within the riparian zone and, thus, contribute directly to their ecological integrity and societal value. Numerous researchers from different disciplines publish work on the physical, biological, economic and societal functions of the riparian zone within various physiographic areas. The present paper aims to review the hydrogeomorphic processes of unconfined alluvial channel-floodplain rivers within the temperate zone. These processes and their interactions with the biotic environment provide the basis for understanding the physical as well as the ecological functioning of fluvial hydrosystems. The review focuses mainly on the European context, but major advances in riparian research from other continents are also considered. Rehabilitation and management strategies for the riparian zone are summarized and recommendations for further research conclude this review. Copyright © 2005 John Wiley & Sons, Ltd.

Land-use change, sediment production and channel response in upland regions

Abstract: Human-induced modifications of the vegetation cover in river basins may cause strong geomorphic responses by disturbing sediment supply, transport and deposition regimes. The response is particularly noticeable in upland regions, where sensitivity to change is enhanced by strong coupling between river channels and hillslopes, as is exemplified by studies undertaken in the East Coast region, North Island, New Zealand, and in the Southern French Prealps. Both regions have been affected by land-use change during the past 150 years (deforestation and reforestation) that can be chronologically linked to geomorphic change on hillslopes and on valley floors. In this paper we use these studies to draw attention to: (1) the magnitude of the change in sediment production associated with a modification to the vegetation cover; (2) the impact that reforestation has on the sediment production and the channel system; and (3) the relative influence of anthropogenic and climatic forcing on the channel response. Finally, we consider the manner in which land use has been used as a tool to manage sediment production in France and New Zealand. The results obtained in both regions demonstrate the strong effect that the vegetation cover has on hillslope erosion processes, through its impact on the landsliding threshold (in New Zealand) and the total sediment yield (from paired forested and non-forested catchments in France). Consideration of channel response serves to emphasize the sensitivity of upland regions to land-use change, and suggests that the successful discrimination between the respective influences of climatic and land-use change depends, in large part, upon the ability to detect spatial and chronological links (or, conversely, gaps) between causes and effects. Copyright © 2005 John Wiley & Sons, Ltd.

Present state of rivers and streams in Japan

Abstract: The Japanese Archipelago (land area: 377 880 km 2 ) extends over a distance of c. 2000 km, with a maximum width of 300 km. Geologically, it is a young and tectonically very active area. Japan is a mountainous, wet and forested country, with its people concentrated in densely populated urban areas along the coast and on alluvial plains. Rivers are short (max. length: 370 km), steep, and exhibit flashy flow regimes. The river regime coefficient ranges from 200 to 400, which is up to an order-of-magnitude higher than that of most continental rivers. Japan has a rich freshwater fauna and flora with a high proportion of endemic species. A distinct latitudinal gradient (subarctic to subtropical climate) in combination with the radial character of the river network results in high spatial differentiation of the freshwater fauna. While water quality has improved remarkably during the past decades, Japanese rivers are still heavily impacted by canalization, loss of most dynamic flood plains, flow regulation, invasion by exotic species, and intensive urbanization. Currently 49% of the entire human population concentrates on 14% of the land, and the annual flood damage is the highest worldwide. As a consequence, major recent restoration initiatives aim to protect people and property against floods as well as simultaneously improving the ecological integrity of river ecosystems.

Waterbird breeding and environmental flow management in the Macquarie Marshes, arid Australia

Abstract: Colonial waterbirds breed in relatively few parts of Australia and the Macquarie Marshes are one of the more important wetlands for these species on the continent in terms of size of breeding colonies and frequency of breeding. Breeding data were collected for ten species of colonial waterbirds in the period 1986-2001: Little Black Cormorant Phalacrocorax sulcirostris, Little Pied Cormorant P. melanoleucos, Great Egret Ardea alba, Intermediate Egret A. intermedia, Little Egret A. garzetta, Cattle Egret A. ibis, Rufous Night Heron Nyctiorax caledonicus, Glossy Ibis Plegadis falcinellus, Straw-necked Ibis Threskiornis spinicollis and Australian White Ibis T. molucca. Breeding of most colonial waterbirds in the Macquarie Marshes was positively related to flow in the three months before breeding and triggered when flows were usually above 200 000 Ml. Flow was also positively related to wetland area. These relationships allowed modelling of three different options for management of environmental flow, nominally an annual allocation of 125 000 Ml. Even though the Macquarie River is highly regulated, there were predicted to be major differences in breeding frequency, flow variability and wetland flooding for different options delivering environmental flows. Use of all environmental flows each year provided the least variable option while accumulating the flow in the major dam and delivering it at high thresholds provided considerably more variability for the Macquarie Marshes, increased breeding of colonial waterbirds and increased frequency of large floods. The size of a waterbird breeding event and flooding extent were still primarily affected by river flooding and diversions upstream, despite the amount of environmental flow and the predicted ecological differences among the environmental flow options.

Flow regime alterations under changing climate in two river basins: implications for freshwater ecosystems

Abstract: We examined impacts of future climate scenarios on flow regimes and how predicted changes might affect river ecosystems. We examined two case studies: Cle Elum River, Washington, and Chattahoochee–Apalachicola River Basin, Georgia and Florida. These rivers had available downscaled global circulation model (GCM) data and allowed us to analyse the effects of future climate scenarios on rivers with (1) different hydrographs, (2) high future water demands, and (3) a river–floodplain system. We compared observed flow regimes to those predicted under future climate scenarios to describe the extent and type of changes predicted to occur. Daily stream flow under future climate scenarios was created by either statistically downscaling GCMs (Cle Elum) or creating a regression model between climatological parameters predicted from GCMs and stream flow (Chattahoochee–Apalachicola). Flow regimes were examined for changes from current conditions with respect to ecologically relevant features including the magnitude and timing of minimum and maximum flows. The Cle Elum's hydrograph under future climate scenarios showed a dramatic shift in the timing of peak flows and lower low flow of a longer duration. These changes could mean higher summer water temperatures, lower summer dissolved oxygen, and reduced survival of larval fishes. The Chattahoochee–Apalachicola basin is heavily impacted by dams and water withdrawals for human consumption; therefore, we made comparisons between pre-large dam conditions, current conditions, current conditions with future demand, and future climate scenarios with future demand to separate climate change effects and other anthropogenic impacts. Dam construction, future climate, and future demand decreased the flow variability of the river. In addition, minimum flows were lower under future climate scenarios. These changes could decrease the connectivity of the channel and the floodplain, decrease habitat availability, and potentially lower the ability of the river to assimilate wastewater treatment plant effluent. Our study illustrates the types of changes that river ecosystems might experience under future climates. Copyright © 2005 John Wiley & Sons, Ltd.

Modelling floodplain inundation on a regulated river: integrating GIS, remote sensing and hydrological models

Abstract: The lower River Murray in South Australia is highly regulated through weirs and water extraction for irrigation. Management of the river for environmental purposes requires an understanding of the extent of floodplain inundation from various flows and weir manipulations. This study aimed to produce a floodplain inundation model for the 600 km long and 1–5 km wide portion of the River Murray in South Australia from the New South Wales border to Lake Alexandrina. The model was developed using a Geographical Information System (GIS), remote sensing and hydrological modelling. Flood inundation extents were monitored from Landsat satellite imagery for a range of flows, interpolated to model flood growth patterns and linked to a hydrological model of the river. The resulting model can be analysed for flows ranging from minimum flow to a 1-in-13-year flood event for any month and weir configuration and has been independently tested using aerial photography to an accuracy of approximately 15% underestimate. The results have proven the approach for determining flood inundation over a large area at approximately one-tenth of the cost of detailed elevation and hydrodynamic modelling. The GIS model allows prediction of impacts on infrastructure, wetlands and floodplain vegetation, allowing quantitative analysis of flood extent to be used as an input into the management decision process. Copyright © 2005 John Wiley & Sons, Ltd.

Catchment-scale controls on groundwater-surface water interactions in the hyporheic zone: implications for salmon embryo survival

Abstract: The spatial and temporal variability of groundwater–surface water (GW–SW) interactions in the hyporheic zone were investigated in a semi-pristine upland salmon spawning catchment (Girnock Burn) in the Cairngorm Mountains, northeast Scotland. Stream and hyporheic water quality (200–300 mm depth) were monitored fortnightly at 16 spawning locations distributed throughout the catchment. Hydrochemical tracers were used to assess local GW–SW interactions. Stratified streambed incubators (50–300 mm) provided information on salmon embryo mortality at a sub-set of ten locations. Hyporheic water quality varied both temporally and spatially according to local GW–SW interactions. It was possible to categorize sites into three broad typologies reflecting local stream–aquifer interactions: (1) groundwater-dominated; (2) surface water-dominated; and (3) sites exhibiting transient water table features. Groundwater upwelling occurred in areas where low permeability glacial moraine features caused substantive valley constriction. These locations were also conducive to accumulation of spawning grade gravels and consequently were utilized heavily by spawning salmon. Long residence groundwater was typically characterized by low dissolved oxygen (DO), of sufficiently low quality to be detrimental to salmon embryo survival. At sites dominated by surface water, hyporheic DO remained high throughout and rates of embryo survival were correspondingly high. Survival rates were also high at sites where hydrochemical characteristics indicated a transient water table. This is probably attributable to the hydrological conditions which resulted in increasing DO concentrations towards hatch time when embryo oxygen demand is at its maximum. The degree to which the findings of this study are directly applicable to other catchments is currently unknown. However, similar effects have been observed elsewhere, and based on the information presented here, there are clear implications for fisheries managers who may wish to consider the use of surface incubation facilities to negate the effects of low DO groundwater upwelling where it dominates available spawning habitat. It is suggested that future research should aim to integrate across spatial scales and disciplines to obtain a better understanding of the ways in which hillslope and riparian zone hydrology affect GW–SW interactions, hyporheic zone processes and stream ecology. © Crown copyright 2005. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

Improved eco‐hydrological classification of rivers

Abstract: The flow regime is recognized as a key factor determining biological and physical processes and characteristics in rivers. Because of this, there is interest in classification and regionalization of rivers in order to delineate patterns in flow regime character at landscape scales. The River Environment Classification (REC) is an a priori mapped classification of rivers. The REC is based on a hierarchical model of ‘controlling factors’, which are assumed to be the dominant causes of variation in physical and biological characteristics of rivers at a variety of spatial scales. The first and second levels of the REC are based on climate and topography and are expected to discriminate rivers according to differences in their flow regimes. Classes are assigned to individual ‘sections’ of the river network based on categorical description of the climate and topography of each section's unique watershed. This paper describes a test of the REC's ability to explain variation in hydrological character of rivers. Flows that were measured continuously at 335 sites distributed throughout New Zealand were summarized by 13 flow variables and were classified using the REC. Principal components analysis was used to show that the REC classes have distinctive flow regime characteristics. We quantified the classification strength (i.e. the extent to which the mean between-class inter-site dissimilarity exceeds the mean within-class inter-site hydrological dissimilarity) of the REC based on the 13 flow variables. The classification strength of the REC was greater than for two existing regionalizations and a classification that is based on climate, but which does not account for the river network. We attribute the increased classification strength of the REC to its explicit consideration of the causes of spatial variation in flow regimes among rivers and its representation of the network spatial structure of rivers. Copyright © 2005 John Wiley & Sons, Ltd.

Effects of stream flow intermittency on riparian vegetation of a semiarid region river (San Pedro River, Arizona)

Abstract: The San Pedro River in the southwestern United States retains a natural flood regime and has several reaches with perennial stream flow and shallow ground water. However, much of the river flows intermittently. Urbanization-linked declines in regional ground-water levels have raised concerns over the future status of the riverine ecosystem in some parts of the river, while restoration-linked decreases in agricultural ground-water pumping are expected to increase stream flows in other parts. This study describes the response of the streamside herbaceous vegetation to changes in stream flow permanence. During the early summer dry season, streamside herbaceous cover and species richness declined continuously across spatial gradients of flow permanence, and composition shifted from hydric to mesic species at sites with more intermittent flow. Hydrologic threshold values were evident for one plant functional group: Schoenoplectus acutus, Juncus torreyi, and other hydric riparian plants declined sharply in cover with loss of perennial stream flow. In contrast, cover of mesic riparian perennials (including Cynodon dactylon, an introduced species) increased at sites with intermittent flow. Patterns of hydric and mesic riparian annuals varied by season: in the early summer dry season their cover declined continuously as flow became more intermittent, while in the late summer wet season their cover increased as the flow became more intermittent. Periodic drought at the intermittent sites may increase opportunities for establishment of these annuals during the monsoonal flood season. During the late summer flood season, stream flow was present at most sites, and fewer vegetation traits were correlated with flow permanence; cover and richness were correlated with other environmental factors including site elevation and substrate nitrate level and particle size. Although perennial-flow and intermittent-flow sites support different streamside plant communities, all of the plant functional groups are abundant at perennial-flow sites when viewing the ecosystem at broader spatial and temporal scales: mesic riparian perennials are common in the floodplain zone adjacent to the river channel and late-summer hydric and mesic annuals are periodically abundant after large floods. Copyright © 2005 John Wiley & Sons, Ltd.

The impact of cold water releases on the critical period of post-spawning survival and its implications for Murray cod (Maccullochella peelii peelii) : A case study of the Mitta Mitta River, Southeastern Australia

Abstract: The effects of cold water releases, as a by-product of storing irrigation water in large dams, has been a source of great concern for its impact on native freshwater fish for some time. The Mitta Mitta River, northeast Victoria, is impacted by altered thermal regimes downstream of the fourth largest dam in Australia, Dartmouth dam, with some daily temperatures 10–12°C below normal. Murray cod (Maccullochella peelii peelii) were endemic to the Mitta Mitta River; however, resident Murray cod have not been found in this river since 1992. The response of eggs and hatched larvae from Murray cod to different temperature gradients of water were measured and the post-spawning survival recorded. As a case study, post-spawning survival was then inferred from flow data for each year of operation of Dartmouth Dam, recorded since first operation in 1978, and included in a stochastic population model to explore the impact of the altered (historical) thermal regime on population viability. Experimental results revealed no egg and larval survival below 13°C and predicted historical temperature regimes point to more than 15 years of low temperatures in the Mitta Mitta River. Population modelling indicates that the impact of cold water releases on post-spawning survival is a significant threatening process to the viability of a Murray cod population. Additionally, we consider changes to the thermal regime to explore how the thermal impact of large dams may be minimized on downstream fish populations through incrementally increasing the temperature of the releases. The modelled Murray cod population responds to minor increases in the thermal regime; however, threats are not completely removed until an increase of at least 5–6°C. Copyright © 2005 John Wiley & Sons, Ltd.

Response of a river sediment budget after historical gravel mining (the lower Tordera, NE Spain)

Abstract: The channel of the lower Tordera River (Catalan Coastal Ranges) was intensively mined between 1956 and 1987, at an extraction rate 14 times higher than the replenishment rates. Mining caused incision of up to 2 m over the whole reach, leading to damage of infrastructures and affecting the groundwater system. In this paper we analyse the response of the river sediment budget by means of sediment transport measurements (both in suspension and as bedload) and topographic surveys. Historical data on mining activities was used to verify current values of sediment transport and to locate the main extraction areas in the long profile of the river. This has led to an integrated methodology that can be useful for assessing and managing current and future sediment deficits in heavily mined rivers. In the lower Tordera, a minimum of 3 million cubic metres of sand and gravel were extracted, especially from two gravel pits still visible as concavities in the river's longitudinal profile. Nowadays, 15 yr after mining ceased, the river shows during dry periods a general tendency towards aggradation (3.6 mm yr−1 on average and up to 12 mm yr−1 in central sections where mining took place), but a slight long-term tendency to erode the riverbed. Sediment yield at the entrance of the study reach attains 552 000 t yr−1, while net sediment deposition reaches 16 400 t yr−1 (78% as bedload), mostly during small floods in dry periods. Estimated time for the river to recover pre-extraction bed-level is of the order of 420 yr. Copyright © 2005 John Wiley & Sons, Ltd.

PHABSIM modelling of Atlantic salmon spawning habitat in an upland stream: testing the influence of habitat suitability indices on model output

Abstract: This paper reports the findings of research designed to assess the ability of PHABSIM to predict Atlantic salmon Salmo salar spawning habitat in the Girnock Burn, a tributary of the River Dee in northeast Scotland. It used an 18-year spawning data record to assess: (a) the ability of PHABSIM to predict between-year differences in the availability of habitat at the study site; (b) the ability of PHABSIM to predict patterns of relative suitability across the site; and (c) the influence of different Habitat Suitability Indices (HSIs) on the model's predictions with respect to (a) and (b). Predictions of between-year and within-site habitat availability based on ‘utilization’ and ‘preference’ HSIs developed in the Dee catchment corresponded significantly (chi-squared and regression tests, P < 0.05) with the use of the site by spawning fish. However, predictions based on utilization HSIs developed in streams in southern England did not correspond significantly with patterns of site use. Results of the study indicate that PHABSIM is capable of predicting Atlantic salmon spawning habitat in upland streams such as the Girnock, but that the use of appropriate HSIs is critical. Copyright © 2005 John Wiley & Sons, Ltd.

Effects of gravel augmentation on macroinvertebrate assemblages in a regulated California River

Abstract: Enhancement projects within anadromous salmonid rivers of California have increased in recent years. Much of this work is intended as mitigation in regulated streams where salmon and steelhead spawning habitat is inaccessible or degraded due to dams, water diversions and channelization. Little research has been done to assess the benefits of spawning habitat enhancement to stream organisms other than salmon. We monitored benthic macroinvertebrates at seven spawning gravel augmentation sites in the lower Mokelumne River, a regulated stream in the Central Valley of California. Placement of cleaned floodplain gravel decreased depths and increased stream velocities. Benthic organisms colonized new gravels quickly, equalling densities and biomass of unenhanced spawning sites within 4 weeks. Macroinvertebrate species richness equalled that of unenhanced sites within 4 weeks and diversity within 2 weeks. Standing crop, as indicated by densities and dry biomass, was significantly higher in enhancement sites after 12 weeks than in unenhanced sites and remained so over the following 10 weeks. Although mobile collector/browsers initially dominated new gravels, sedentary collectors were the most common feeding category after 4 weeks, similar to unenhanced sites. These data suggest that cleaned gravels from adjacent floodplain materials, used to enhance salmonid spawning sites, are quickly incorporated into the stream ecosystem, benefiting benthic macroinvertebrate densities and dry biomass. Copyright © 2005 John Wiley & Sons, Ltd.

Tests of Two Types of Bypass for Downstream Migration of Eels at a Small Hydroelectric Power Plant

Abstract: Efficiencies of two types of bypass, a surface and a bottom sluice, were tested for the natural downstream migration of silver eels Anguilla anguilla at a small hydroelectric power plant at Halsou, on the River Nive in France. Naturally migrating eels were caught after their passage through either bypass. A total of 637 eels were trapped during the three-year study. Total efficiency for both bypasses, evaluated on the basis of downstream movement of radiotagged eels, ranged from 56% to 64%. Given a bias due to hydrological conditions at the time of the runs, the precise efficiency of each separate bypass was not calculated. However, preferred passage through the bottom bypass for both tagged and untagged eels was confirmed by telemetry, as three to four times as many eels transited through the bottom bypass compared to the surface one. The behaviour of 74 individuals released in the forebay was observed by radiotelemetry. Close to half of the radiotagged eels returned up the headrace after their release, and most eventually migrated downstream over the dam with appropriate environmental conditions. Upon arrival at the power plant, eels displayed foraging behaviour in the forebay with frequent displacement interrupted by long resting periods in zones with low current. The repulsive effect of the trashrack located in front of the turbine intake increased with increasing turbined discharge. The study indicated that a trashrack with a smaller bar-spacing (around 20 mm), associated with an appropriate bypass, could deflect a large proportion of the female eels from the turbines. However, this solution needs to be tested on site to quantify the risk of mortality due to impingement on the trashrack. Copyright © 2005 John Wiley & Sons, Ltd.

Seed inputs in riparian zones: implications for plant invasion

Abstract: Seed inputs were studied from January 2001 to August 2002 along a tranverse successional gradient of a riparian zone within the mid-reaches of the Garonne River (SW France). Seeds were trapped monthly at ten sites distributed along the gradient. In total, 117 000 seeds belonging to 296 species were collected, among which 145 were exotic species. Seed inputs were overall dissimilar to the extant vegetation; however, similarity among seed input samples was higher than similarity among the extant vegetation samples. Exotic seed inputs resulted from distinct modes of dispersal in comparison to the native ones. Exotic guilds also comprised more short-lived species. A significant positive linear relationship was observed between exotic and native species richness for both seed inputs and extant vegetation. Flood events were responsible for species richness peaks in seed inputs. They also contributed towards peaks in exotic species and individuals. However, most exotic seeds were recruited during low water period, with a significant lag in time compared to native inputs. Species composition, densities of species and individuals as well as the percentages of exotic species distinguished the infrequently agricultural zone from the frequently disturbed riparian zone. The latter zone was the most invaded both in terms of seed input and extant vegetation.

Accessing limnological change and variability using fossil diatom assemblages, south‐east Australia

Abstract: Floodplain wetlands accumulate river-borne sediments that include mixed assemblages of allochthonous and autochthonous diatoms as fossils. These assemblages have been used in river floodplain wetlands and reservoirs to quantitatively reconstruct salinity, pH and nutrients and to qualitatively infer connectivity and turbidity over periods spanning decades to millennia. High sedimentation rates in some sites have permitted sub-annual temporal resolution; however, annual to decadal resolution is more usual. The establishment of chronologies for these sequences is often difficult owing to the substantial input of fluvially borne 210 Pb, the high spatial variability in the earliest detection of exotic pollen markers and the inaccuracy of radiocarbon approaches in dating sediments younger than 500 years. Other complexities arise from the difficulty of differentiating the influence of co-variables in accord with the river continuum concept and identifying shifts driven by hydroseral influences independent of changes to the fluvial system. Caution is also needed in inferring lotic change from a record accumulating in lentic systems. Nevertheless, substantial increases in salinity (lower Snowy, lower and middle Murray), pH (mid-Goulburn), turbidity (upper and lower Murray and Yarra), nutrients (lower Murray and Yarra), and sedimentation rate (widespread), as well as clear shifts in trophic structure (upper Murray), have been documented for the post-European period from regulated river wetlands across southeast Australia. A site in the lower Murray records river connectivity and water quality changes consistent with the regional Holocene climate record. Reductions in effective precipitation documented in closed lake systems are not evident in riverine plain wetlands, possibly owing to their relative complexity. The refinement of chronologies and data-bases will allow the determination of the pre-impact nature and variability of sites, the rates of limnological change and biological responses and the feasibility of rehabilitation targets.

Pre‐ and post‐reforestation gully development in Mangatu Forest, East Coast, North Island, New Zealand

Abstract: Following clearance of the indigenous forest and conversion of the land to pasture early in the 20th century, gully erosion became a pervasive feature in the headwaters of the Waipaoa River basin, and was notably problematic in the 140-km2 area now covered by the Mangatu Forest. In this area, before reforestation in 1961, gully erosion affected c. 4% of the terrain. After a 24-year exotic reforestation programme the area affected by gullies was reduced to 1.5%, but of the eight gullies larger than 10 ha in 1960 none had stabilized by 1988, although four had at least halved in size. Estimates that a gully will stabilize or increase in size under a range of conditions suggest that in the case of gullies 80% probability of stabilization after one forest rotation (c. 24 years). For gullies between 1 and 5 ha in area the probability of stabilization is c. 60%. Gullies of 5 ha have an even chance of stabilizing over the time frame of a single rotation. The key determinant is gully size and shape at the time of planting and, within this size range, these relationships were stronger for linear than for amphitheatre-shaped gullies. Between 1939 and 1988 sediment production from gullies in the portion (76%) of the Mangatu Forest underlain by Cretaceous-aged rock was c. 22 000 t km−2 yr−1, and during the period of maximum sediment production (1939–1960) they may have accounted for c. 17% of the Waipaoa River's average annual suspended sediment load. Reforestation reduced the contribution to c. 8% in the period between 1970 and 1988. However, the off-site (downstream) impact of sediment generated by the remaining 420 active gullies in the Waipaoa River catchment is significant, not least on the capacity of the scheme that protects high-value agricultural land on the Poverty Bay Flats from flooding. A targeted reforestation programme may be an alternative to raising the height of the existing artificial levees. It is estimated that additional exotic plantings totalling c. 15 400 ha (c. 7% of the Waipaoa River basin area) would produce a > 64% reduction in sediment production from gullies on pastoral hillslopes within one forest rotation (c. 24 yr). Copyright © 2005 John Wiley & Sons, Ltd.

River widening : An approach to restoring riparian habitats and plant species

Abstract: ‘River widenings’ are commonly used in river restoration to allow channel movement within a spatially limited area Restoration seeks to restore fluvial processes and to re-establish a more natural riparian community This study investigates the performance of five river widenings in Switzerland, focusing on the re-establishment of riparian (semi-)terrestrial habitats and species, and highlights some factors that seem to influence their performance The restoration projects are compared with pre-restoration conditions and near-natural conditions, which are assumed to represent the worst- and best-case conditions along a gradient of naturalness Fuzzy ordination of vegetation data and calculation of landscape metrics based on habitat maps revealed marked differences between the degree of naturalness achieved by each individual restoration project However, in general river widenings were found to increase the in-stream habitat heterogeneity and enhanced the establishment of pioneer habitats and riparian plants Analyses of species pools based on a hierarchic list of indicator species and correspondence analysis showed that the ability of river widenings to host typical riparian species and to increase local plant diversity strongly depends on the distance to near-natural stretches Species dispersal and establishment might be hampered by decisions taken outside the scope of the restoration project Therefore we conclude that action on the catchment scale is needed to maximize the benefits of local management Copyright © 2005 John Wiley & Sons, Ltd

Comparison of blockage factors in modelling the resistance of channels containing submerged macrophytes

Abstract: The proportion of a river channel containing vegetation (termed the blockage factor) has historically been determined in three ways: cross-sectional, surface area and volumetric. The first two versions are two-dimensional measures. Meanwhile, the three-dimensional volumetric version is biased towards deeper sections of a reach. A fourth version of the blockage factor is proposed that does not have such limitations: the multi-cross-sectional blockage factor. Between five and nine cross-sections were sampled to determine the four blockage-factor versions for 35 river sites containing the clumped submergent macrophyte, Ranunculus subgenus Batrachium (water-crowfoot). The ability of these four measures to act as predictors of vegetative channel resistance was then assessed. The vegetated proportion of individual cross-sections was poorly related to the vegetation resistance of a channel reach, primarily due to the high spatial variability of patch-forming macrophytes. The weighted median of all cross-sectional blockage factors measured at each site produced the strongest relationship with vegetation resistance, though this was not significantly better than the volumetric or surface area versions. The resistance model using the surface-area blockage factor gave a very high residual between predicted and calculated resistance for a mat-forming macrophyte species, and this model is unlikely to hold for conditions other than baseflow. Likewise, the volumetric version is not expected to hold for sites that have more depth variability than those measured in this study. Copyright © 2005 John Wiley & Sons, Ltd.

Evaluation of nature‐like fishways for re‐establishing connectivity in fragmented salmonid populations in the River Emån

Abstract: We evaluated the function of two nature-like fishways for re-establishing connectivity for anadromous salmonids in the regulated River Eman. Between 90 and 100% of the salmonids that entered the fi ...

Effects of dam‐induced flow regime change on downstream river morphology and vegetation cover in the Hwang River, Korea

Abstract: The Hapchon Dam, located in the headwaters of the Hwang River, Korea, was completed in 1988. Due to low storage levels, the spillway has not been operated over the past decade. Thus, a new ecosystem has become established in the river downstream of the dam. This is not a common phenomenon in Korean rivers. This study investigates the effect of flow regime change on the river morphology and vegetation cover in a reach downstream of the dam following its construction. Geomorphological effects shown by pre- and post-construction surveys of the channel include channel incision over a stream length of approximately 25 km immediately downstream of the dam. Analysis of pre- and post-construction aerial photography reveals significant encroachment of riparian vegetation onto previously active bar surfaces.

Application of wavelet analysis for monitoring the hydrologic effects of dam operation: Glen Canyon Dam and the Colorado River at Lees Ferry, Arizona

Abstract: Wavelet analysis is a powerful tool with which to analyse the hydrologic effects of dam construction and operation on river systems. Using continuous records of instantaneous discharge from the Lees Ferry gauging station and records of daily mean discharge from upstream tributaries, we conducted wavelet analyses of the hydrologic structure of the Colorado River in Grand Canyon. The wavelet power spectrum (WPS) of daily mean discharge provided a highly compressed and integrative picture of the post-dam elimination of pronounced annual and sub-annual flow features. The WPS of the continuous record showed the influence of diurnal and weekly power generation cycles, shifts in discharge management, and the 1996 experimental flood in the post-dam period. Normalization of the WPS by local wavelet spectra revealed the fine structure of modulation in discharge scale and amplitude and provides an extremely efficient tool with which to assess the relationships among hydrologic cycles and ecological and geomorphic systems. We extended our analysis to sections of the Snake River and showed how wavelet analysis can be used as a data mining technique. The wavelet approach is an especially promising tool with which to assess dam operation in less well-studied regions and to evaluate management attempts to reconstruct desired flow characteristics. Copyright © 2005 John Wiley & Sons, Ltd.

Optimizing dam release rules to meet environmental flow targets

Abstract: Linking environmental flow dam release rules to environmental variables has potential to link the flow variability of a regulated stream to the environmental forces acting on the catchment. A technique is developed to examine a range of release rules related to gauged tributary inflows and optimize these with respect to total water release volumes and other criteria. A model is created consisting of three parts: (1) a Dam Release Event Generator, which generates dam releases according to a set of rules, (2) a simple routing model using linear transforms and derived time-series for ungauged tributary inflows, (3) an algorithm to analyse the output time-series and produce statistics on the environmental flows. This model is run for a range of rule parameters within a parameter space. The results showed that multiple strategies might be capable of achieving the required targets but that some of these may be more robust in the face of climate variability than others. Significant water savings can result from the use of the technique. However, the results also highlight the limitations of the way environmental flows are currently stipulated and point towards a new generation of environmental flows. The technique is applied to environmental flow targets in the Thomson River catchment, Victoria, Australia. Copyright © 2005 John Wiley & Sons, Ltd.

The effect of altered flow regime on the frequency and duration of bankfull discharge: Murrumbidgee River, Australia

Abstract: On meandering rivers with well-developed floodplains, bankfull stage has geomorphological and ecological significance because it approximates the level of connection between the channel and the floodplain. As a river rises to bankfull stage, sediment begins to be deposited on the floodplain, wetlands are progressively inundated and organisms migrate between the channel and floodplain habitats. On many rivers large headwater dams have reduced the frequency and duration of floodplain inundation downstream. However, the lack of reliable pre-regulation flow data has made it difficult to quantify the effects of river regulation. This study used historical regulated and modelled natural flow data to determine the effects of regulation on the frequency and duration of bankfull flows on the Murrumbidgee River, one of Australia's largest and most heavily regulated rivers. In combination with floodplain surveys the flow data show that regulation has halved the frequency and duration of bankfull flows. This reduction in channel–floodplain connection has implications for the ecological health of the Murrumbidgee River. Copyright © 2005 John Wiley & Sons, Ltd.

Measuring the reach-scale geomorphic diversity of streams: application to a stream disturbed by a sediment slug

Abstract: There is increasing evidence that greater physical diversity in a stream leads to a greater diversity of habitats, and hence species. Human impact has reduced the physical diversity within many stream systems. This paper reviews a range of techniques used to measure the physical diversity of a stream reach and specifically examines variability measures of a stream's thalweg, cross-section and sediment size at the scale of millimetres to metres. Each measure was evaluated against synthetic data with different levels of diversity. From the original thirteen, eight measures were considered appropriate for application to data measured in the field. Creightons Creek (Victoria, Australia) was selected as a test site as it contains areas that are in their original geomorphic condition, as well as sections that have been disturbed by increased bed-load in the form of a sediment slug. All eight measures showed that the area impacted by the sediment slug was less diverse in terms of its geomorphic variability than the unimpacted reaches. This suggests that massive increases in sediment load to streams will reduce the geomorphic complexity of a stream, and in turn, the diversity of habitat for biological communities. Copyright © 2005 John Wiley & Sons, Ltd.

Assessing the effectiveness of enhancement activities in urban streams: II. Responses of invertebrate communities

Abstract: The effects of habitat enhancement on the invertebrate communities in five urban streams in Christchurch, New Zealand, were investigated. All streams underwent riparian planting, while extensive channel modifications were made at two streams, where a concrete dish channel and a wooden timber-lined stream were removed and natural banks reinstated. Benthic invertebrates were collected before enhancement and 5 years after from the same locations. Invertebrates were also collected from control sites in each stream in 2001. Desired goals of enhancement activities included increasing the densities of mayflies and caddisflies, and decreasing densities of oligochaetes, snails and midges. Enhancement activities changed riparian vegetation and bank conditions, as well as substrate composition, instream organic matter and variability of instream velocities. Invertebrate communities prior to enhancement were typical of those in urban environments, and dominated by snails (Potamopyrgus, Physa), the amphipod Paracalliope, the hydroptilid caddisfly Oxyethira, oligochaetes and chironomids. Stream enhancement caused only small changes to the invertebrate community, with subtle shifts in overall abundance, species evenness, diversity, and ordination scores. Lack of a consistent strong response by invertebrates to enhancement activities, and continued absence of caddisflies and mayflies from enhanced sites may reflect lack of sufficient change to instream conditions as a result of stream enhancement, colonization bottlenecks for aerial stages of these animals, and the inability of individuals outside the urban watershed to perceive these enhanced ‘islands’ of good habitat. Alternatively, contamination of streambed sediments, excess sedimentation and reduced base flows may be limiting factors precluding successful invertebrate colonization in enhanced sites. These results highlight the importance of setting clear goals and objectives necessary to meet these goals. Enhancement of riparian zones in urban streams may not be adequate to improve benthic invertebrate communities. Identifying over-arching factors that potentially limit invertebrate communities will enable the enhancement potential of streams to be better assessed, and allow managers to identify sites where recovery of biological communities is possible, and where such recovery is not. Copyright © 2005 John Wiley & Sons, Ltd.