Mean Annual River Flow Research Articles

Historical climate impact attribution of changes in river flow and sediment loads at selected gauging stations in the Nile basin

The Nile basin is the second largest basin in Africa and one of the regions experiencing high climatic diversity with variability of precipitation and deteriorating water resources. As climate change is affecting most of the hydroclimatic variables across the world, this study assesses whether historical changes in river flow and sediment loads at selected gauges in the Nile basin can be attributed to climate change. An impact attribution approach is employed by constraining a process-based model with a set of factual and counterfactual climate forcing data for 69 years (1951–2019), from the impact attribution setup of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3a). To quantify the role of climate change, we use the non-parametric Mann-Kendall test to identify trends and calculate the differences in long-term mean annual river flow and sediment load simulations between a model setup using factual and counterfactual climate forcing data. Results for selected river stations in the Lake Victoria basin show reasonable evidence of a long-term historical increase in river flows (two stations) and sediment load (one station), largely attributed to changes in climate. In contrast, within the Blue Nile and Main Nile basins, there is a slight decrease of river flows at four selected stations under factual climate, which can be attributed to climate change, but no significant changes in sediment load (one station). These findings show spatial differences in the impacts of climate change on river flows and sediment load in the study area for the historical period.

The role of tides, river discharge and wind on the residual circulation of Maputo Bay

Lateral variability of residual flow was investigated in Maputo Bay in Mozambique, Africa. The bay is nearly rectangular with 30×30 km, mean depth of 5 m. The bay mouth is ∼18 km wide with mean and maximum depth ∼10 m and 30 m, respectively. Tides ranges between 1 and 3 m at neap and spring tides, respectively. The mean annual river flow is ∼225 m3/s, ranging from ∼150 to ∼400 m3/s during winter and summer, respectively. Southeasterly (SE) wind are the most frequent wind during the year followed by northeasterly (NE) winds. In order to scale the relative importance of tides, wind and buoyancy effects on the residual exchange flows, we designed three-dimensional numerical experiments (Delft3D). Results show strong changes among the scenarios and between neap and spring tide conditions. During spring tide, flows becomes more vertically homogeneous and laterally sheared, modulated by the cross-section shape. Most important exchange flows were during neap tides mainly with scenarios forced by tides. There are some locations prone to entrap sediments, such as the inlet of the Incomati river and to the north of Inhaca Isle.

Hydrological time series forecasting using simple combinations: Big data testing and investigations on one-year ahead river flow predictability

Delivering useful hydrological forecasts is critical for urban and agricultural water management, hydropower generation, flood protection and management, drought mitigation and alleviation, and river basin planning and management, among others. In this work, we present and appraise a new simple and flexible methodology for hydrological time series forecasting. This methodology relies on (a) at least two individual forecasting methods and (b) the median combiner of forecasts. The appraisal is made by using a big dataset consisted of 90-year-long mean annual river flow time series from approximately 600 stations. Covering large parts of North America and Europe, these stations represent various climate and catchment characteristics, and thus can collectively support benchmarking. Five individual forecasting methods and 26 variants of the introduced methodology are applied to each time series. The application is made in one-step ahead forecasting mode. The individual methods are the last-observation benchmark, simple exponential smoothing, complex exponential smoothing, automatic autoregressive fractionally integrated moving average (ARFIMA) and Facebook’s Prophet, while the 26 variants are defined by all the possible combinations (per two, three, four or five) of the five afore-mentioned methods. The new methodology is identified as well-performing in the long run, especially when more than two individual forecasting methods are combined within its framework. Moreover, the possibility of case-informed integrations of diverse hydrological forecasting methods within systematic frameworks is algorithmically investigated and discussed. The related investigations encompass linear regression analyses, which aim at finding interpretable relationships between the values of a representative forecasting performance metric and the values of selected river flow statistics. We find only loose (but not negligible) relationships between the formed variable sets. These relationships could be exploited for improving (to some extent) future forecasting applications. The results of our big data forecasting experiment are lastly exploited for characterizing –in relative terms– one-year ahead river flow predictability. We believe that our findings have both practical and theoretical implications.

Comparison of watershed sediment delivery estimates of 60 Michigan rivers using the USACE Great Lakes regional trend line and the Syvitski and Milliman global BQART equation

The purpose of this research was to compare annual watershed sediment delivery estimates for 60 Michigan rivers using two fundamentally different approaches: the Great Lakes regional trend line that was developed by the U.S. Army Corps of Engineers (USACE) and the global BQART watershed sediment delivery equation that was developed by Syvitski and Milliman (2007). In addition, for six of the 60 watersheds, the global BQART equation and the USACE Great Lakes regional trend line were compared to watershed sediment delivery estimates that were prepared by the USACE using complex, calibrated hydrodynamic and sediment delivery models. The USACE Great Lakes regional trend line is an empirical equation that was developed based on sediment delivery estimates from 48 reservoirs and 13 watersheds located throughout the Great Lakes basin and predicts watershed sediment delivery based on watershed area (R2 = 0.78). The Syvitski and Milliman BQART equation was developed from a database encompassing 488 global rivers whose watersheds cover 63% of the earth’s surface. The BQART equation estimates watershed sediment delivery as dependent on five variables including: a geologic and human influence factor (B), the mean annual flow of the river (Q), watershed area (A), the difference between the maximum elevation of the watershed and the elevation of the receiving water (relief; R), and, mean basin temperature (T). The global BQART sediment delivery equation was validated for rivers with mean annual flows exceeding 30 m3/s. The watersheds for the 60 Michigan rivers evaluated in the present research cover 128,043 kilometers2, and the mean annual river flows range from 1.0 m3/s (Days River) to 132.5 m3/s (St. Joseph River), and average 22 m3/sec. Overall, the watershed sediment delivery estimates for these 60 rivers using the global BQART equation were 19% lower than those based on the USACE Great Lakes regional trend line and were within 25% of the USACE regional trend line for 21 of the 60 rivers evaluated. With respect to the 12 Michigan rivers with mean annual flows greater than 30 m3/sec, the global BQART sediment delivery estimates were on average 32% higher than the USACE Great Lakes regional trend line. Of the remaining 48 rivers with mean annual flows of less than 30 m3/s, the global BQART sediment delivery estimates were on average 31% lower than the USACE Great Lakes regional trend line. The global BQART equation provided close estimates of watershed sediment delivery for 21 of the 60 Michigan rivers evaluated in this research in comparison to the USACE Great Lakes regional trend line, especially for rivers with mean annual flows greater than 30 m3/s. This implies that the global and Great Lakes regional processes of soil erosion and deposition, and sediment transport to the river outlet are similar, especially for the large Michigan watersheds. Regression analysis comparing the terms of the global BQART equation to the 60 watershed sediment delivery estimates developed using the USACE (2010) Great Lakes regional trend line revealed that the most important variables affecting watershed sediment delivery are watershed area (A), mean annual river flow (Q), and relief (R).

Svyaz' morfometricheskikh kharakteristik vodosborov i landshaftnykh uslovij v bassejne r. Avachi (Kamchatka) s kharakteristikami srednegodovogo i maksimal'nogo stoka rek

Svyaz' morfometricheskikh kharakteristik vodosborov i landshaftnykh uslovij v bassejne r. Avachi (Kamchatka) s kharakteristikami srednegodovogo i maksimal'nogo stoka rek

Sink or swim? Potential for high faunal turnover in Australian rivers under climate change

AbstractAimClimate change threatens biodiversity in all ecosystems, and major shifts in species distributions are expected. Freshwater ecosystems are considered particularly vulnerable due to the ectothermic physiology of most freshwater species and their limited habitat extent and capacity to track climate trends. In this study, we examined what broad patterns in freshwater riverine species turnover might be expected under climate change across continental Australia and what are the implications of these patterns for aquatic species and the low aquatic biodiversity of some bioregions?LocationContinental Australia.MethodsWe built statistical relationships between bioclimatic environments and the occurrence of species of four freshwater taxa (freshwater fish, crayfish, turtles and frogs) and examined trends in projected species turnover for a ‘business as usual’ climate scenario. We used Maxent to model species distributions and present the median projection across 18 global climate models. A recently derived national stream network was used to generate estimates of mean annual river flow and to produce realistic species distributions and migration options by restricting dispersal and migration opportunities usually available to riverine fauna.ResultsHigh species turnover was driven overwhelmingly by potential local extinctions particularly for stream frogs and crayfish where their current biodiversity is largely confined to higher elevation headwater streams. We predicted high turnover for inland regions of Australia, which are arid and generally support fewer freshwater species.Main conclusionsOur analysis indicates that under the most severe emissions pathway, projected climate change is likely to cause substantial changes to the composition of faunal assemblages in Australian rivers well before the end of this century. While freshwater systems globally are subject to immediate and pressing threats from anthropogenic land and water use, management interventions addressing these pressures need to be considered within the context of climate change.

Is the future of large shallow lakes blue-green? Comparing the response of a catchment-lake model chain to climate predictions

We constructed a model chain into which regional climate-related variables (air temperature, precipitation) and a lake’s main tributary hydrological indicators (river flow, dissolved inorganic carbon) were employed for predicting the evolution of planktonic blue-green algae (cyanobacteria) and zooplankton (rotifer) biomass in that lake for the mid-21st century. Simulations were based on the future climate predicted under both the Representative Concentration Pathways 4.5 and 8.5 scenarios which, combined with three realistic policy-making and basin land-use evolution lead to six scenarios for future water quality. Model outputs revealed that mean annual river flow is expected to decline between 3 and 20%, depending on the scenario. Concentration of river dissolved inorganic carbon is predicted to follow the opposite trend and might soar up to twice the 2005–2014 average concentration. Lake planktonic primary producers will display quantitative changes in the future decades whereas zooplankters will not. A 2 to 10% increase in mean cyanobacteria biomass is accompanied by a stagnation (−3 to +2%) of rotifer biomass. Changes in cyanobacteria and rotifer phenology are expected: a surge of cyanobacteria biomass in winter and a shortening of the rotifer biomass spring peak. The expected quantitative changes on the biota were magnified in those scenarios where forested area conversions to cropland and water abstraction were the greatest.

Characteristics and Spatial Segregation of Sympatric Saugers and Walleyes in the Ottawa River, Canada

AbstractFew comparative studies exist on the sympatric populations of Saugers Sander canadensis and Walleyes S. vitreus, especially in northern rivers. Depth‐stratified, standardized index netting surveys were conducted in the Ottawa River, Canada—a large, fragmented northern river. The objectives of this study were to (1) determine whether Saugers and Walleyes were spatially segregated within river reaches; (2) assess whether relative abundances of the two species were correlated within river reaches and ascertain factors affecting their relative abundances; (3) determine whether life history characteristics in this northern river were within the variation reported for each species; and (4) evaluate whether there was synchrony in year‐class strength between the two species and identify the factors affecting year‐class strength. Saugers and Walleyes were spatially segregated, specifically by depth. Probability of capture was greatest in the 20–35‐m depth stratum for Saugers and in the 6–12‐m depth stratum for Walleyes. Relative abundances of Saugers and Walleyes were correlated and were positively related to reach characteristics (i.e., mean and maximum depth, reach length, and river kilometers upstream from the confluence) but negatively related to thermal conditions (i.e., growing degree‐days, water temperature at preferred depths, and human population in proximity to the river). Life history characteristics were within the literature‐reported ranges except for Saugers, which were older with a smaller length at 50% maturity. Year‐class strengths of Saugers and Walleyes were synchronous at the reach and river levels and were positively correlated with mean annual temperature but negatively correlated with mean annual river flow. Saugers and Walleyes can coexist within large water bodies. Recruitment synchrony suggests that spawning management efforts could benefit both species, which could be advantageous when managing the Sauger, a lesser studied species. However, life history differences advocate that harvest regulations (e.g., size limits) must be species specific in order to be effective.Received June 13, 2013; accepted January 27, 2015

Characterization of the Gacka River basin karst aquifer (Croatia): Hydrochemistry, stable isotopes and tritium-based mean residence times

The Gacka River basin aquifer is a highly-developed karst system, located in the Croatian Dinarides. It is mostly composed of permeable Jurassic and Cretaceous carbonate rocks, and clastic sedimentary rocks of Paleogene age. Gacka River provides high quality water for the town of Otočac and several villages; together with the neighboring Lika River, the water is used for the Hydroelectric Power Plant at Senj on the coast. About 10 perennial and over 20 seasonal springs are located at 450 to 460ma.s.l. (above sea level). Three major springs (Pećina, Majerovo and Tonkovića) provide 57% of the mean annual river flow. Similarities between the average groundwater temperatures as well as between the average specific electrical conductivity values (9.0°C-328μS/cm, 9.6°C-350μS/cm and 8.9°C-312μS/cm) of the springs imply that they are fed from aquifers with similar mean residence times (MRTs). The mean δ18O contents of Majerovo, Tonkovića, and Pećina are around −10.1‰, −9.2‰ and −8.9‰, respectively, revealing differences in the mean recharge area elevations. Compared to the temporal amplitude of the18O signal of precipitation, the 18O signal variations of the springs are substantially attenuated because the recharges occurring at different times are well mixed within the aquifers. This indicates MRTs of more than just a few years. The average tritium contents of Pećina, Majerovo and Tonkovića are 5.48TU, 6.13TU and 6.17TU, respectively. Serially connected exponential-plug type unsteady lumped-parameter models run on an annual time scale resulted in rather satisfactory matches between the observed and calculated tritium contents for all studied springs. The models revealed similar MRTs (and corresponding reservoir volumes) for Pećina, Tonkovića and Majerovo of 12years (470Mm3), 12years (1190Mm3), and 12.2years (1210Mm3), respectively. Plug flow conditions dominate in about 90% of the total aquifer volumes.

Rapid dispersal of saltcedar (Tamarix spp.) biocontrol beetles (Diorhabda carinulata) on a desert river detected by phenocams, MODIS imagery and ground observations

We measured the rate of dispersal of saltcedar leaf beetles (Diorhabda carinulata), a defoliating insect released on western rivers to control saltcedar shrubs (Tamarix spp.), on a 63km reach of the Virgin River, U.S. Dispersal was measured by satellite imagery, ground surveys and phenocams. Pixels from the Moderate Resolution Imaging Spectrometer (MODIS) sensors on the Terra satellite showed a sharp drop in NDVI in midsummer followed by recovery, correlated with defoliation events as revealed in networked digital camera images and ground surveys. Ground surveys and MODIS imagery showed that beetle damage progressed downstream at a rate of about 25kmyr−1 in 2010 and 2011, producing a 50% reduction in saltcedar leaf area index and evapotranspiration by 2012, as estimated by algorithms based on MODIS Enhanced Vegetation Index values and local meteorological data for Mesquite, Nevada. This reduction is the equivalent of 10.4% of mean annual river flows on this river reach. Our results confirm other observations that saltcedar beetles are dispersing much faster than originally predicted in pre-release biological assessments, presenting new challenges and opportunities for land, water and wildlife managers on western rivers. Despite relatively coarse resolution (250m) and gridding artifacts, single MODIS pixels can be useful in tracking the effects of defoliating insects in riparian corridors.

Impacts of impervious cover, water withdrawals, and climate change on river flows in the conterminous US

Abstract. Rivers are essential to aquatic ecosystem and societal sustainability, but are increasingly impacted by water withdrawals, land-use change, and climate change. The relative and cumulative effects of these stressors on continental river flows are relatively unknown. In this study, we used an integrated water balance and flow routing model to evaluate the impacts of impervious cover and water withdrawal on river flow across the conterminous US at the 8-digit Hydrologic Unit Code (HUC) watershed scale. We then estimated the impacts of projected change in withdrawals, impervious cover, and climate under the B1 "Low" and A2 "High" emission scenarios on river flows by 2060. Our results suggest that compared to no impervious cover, 2010 levels of impervious cover increased river flows by 9.9% on average with larger impacts in and downstream of major metropolitan areas. In contrast, compared to no water withdrawals, 2005 withdrawals decreased river flows by 1.4% on average with larger impacts in heavily irrigated arid regions of Western US. By 2060, impacts of climate change were predicted to overwhelm the potential gain in river flow due to future changes in impervious cover and add to the potential reduction in river flows from withdrawals, decreasing mean annual river flows from 2010 levels by 16% on average. However, increases in impervious cover by 2060 may offset the impact of climate change during the growing season in some watersheds. Large water withdrawals will aggravate the predicted impact of climate change on river flows, particularly in the Western US. Predicted ecohydrological impacts of land cover, water withdrawal, and climate change will likely include alteration of the terrestrial water balance, stream channel habitat, riparian and aquatic community structure in snow-dominated basins, and fish and mussel extirpations in heavily impacted watersheds. These changes may also require new infrastructure to support increasing anthropogenic demand for water, relocation of agricultural production, and/or water conservation measures. Given that the impacts of land use, withdrawals and climate may be either additive or offsetting in different magnitudes, integrated and spatially explicit modeling and management approaches are necessary to effectively manage water resources for aquatic life and human use in the face of global change.

Intra- to Multidecadal Variations of Snowpack and Streamflow Records in the Andes of Chile and Argentina between 30° and 37°S

Abstract In a recent study the authors developed the first regionally averaged, transnational records of snowpack and streamflow for the Andes between 30° and 37°S using Chilean and Argentinean data. That study was mainly intended to evaluate the relationships between the interannual variations in the regional snowpack record and large-scale atmospheric variables and indices. Here the focus is on the main intra- to multidecadal variations in updated records of winter snowpack and mean annual river flows. River discharges show similar temporal variations on both sides of the Andes with extreme dry conditions concentrated between the mid-1940s and 1976/77 and extreme wet conditions peaking between the late 1970s and the 1980s. A regional streamflow composite (1906–2007) has a nonsignificant negative trend but significant regime shifts in 1945, when mean levels dropped 31%, and in 1977 when they increased 28%. These events coincide almost exactly with well-known shifts in the Pacific decadal oscillation (PDO). The analyses are preliminary but suggest a PDO influence on the low-frequency modes of hydroclimatic variability in the study area. Analyses of the magnitude of 5–20-yr moving windows in the regional streamflow composite indicate that the most significant concentration of high (low) discharges occurred between 1977 and 1987 (1954 and 1971). Snowpack series show a more heterogeneous pattern of variations on a local basis but when aggregated into a regional series (1951–2008) they share remarkable similarities with river flows. However, the snowpack composite has a stronger year-to-year variability, a slight positive trend, and no significant regime shifts.

Climate change impacts on water management and irrigated agriculture in the Yakima River Basin, Washington, USA

The Yakima River Reservoir system supplies water to ~180,000 irrigated hectares through the operation of five reservoirs with cumulative storage of ~30% mean annual river flow. Runoff is derived mostly from winter precipitation in the Cascade Mountains, much of which is stored as snowpack. Climate change is expected to result in earlier snowmelt runoff and reduced summer flows. Effects of these changes on irrigated agriculture were simulated using a reservoir system model coupled to a hydrological model driven by downscaled scenarios from 20 climate models archived by the 2007 Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. We find earlier snowmelt results in increased water delivery curtailments. Historically, the basin experienced substantial water shortages in 14% of years. Without adaptations, for IPCC A1B global emission scenarios, water shortages increase to 27% (13% to 49% range) in the 2020s, to 33% in the 2040s, and 68% in the 2080s. For IPCC B1 emissions scenarios, shortages occur in 24% (7% to 54%) of years in the 2020s, 31% in the 2040s and 43% in the 2080s. Historically unprecedented conditions where senior water rights holders suffer shortfalls occur with increasing frequency in both A1B and B1 scenarios. Economic losses include expected annual production declines of 5%–16%, with greater probabilities of operating losses for junior water rights holders.

Wide‐Area Estimates of Stand Structure and Water Use of Tamarix spp. on the Lower Colorado River: Implications for Restoration and Water Management Projects

Abstract Tamarix spp. removal has been proposed to salvage water and allow native vegetation to recolonize western U.S. riparian corridors. We conducted wide‐area studies on the Lower Colorado River to answer some of the scientific questions about Tamarix water use and the consequences of removal, combining ground surveys with remote sensing methods. Tamarix stands had moderate rates of evapotranspiration (ET), based on remote sensing estimates, averaging 1.1 m/yr, similar to rates determined for other locations on the river and other rivers. Leaf area index values were also moderate, and stands were relatively open, with areas of bare soil interspersed within stands. At three Tamarix sites in the Cibola National Wildlife Refuge, groundwater salinity at the site nearest to the river (200 m) was relatively low (circa 2,250 mg/L) and was within 3 m of the surface. However, 750 and 1,500 m from the river, the groundwater salinity was 5,000–10,000 mg/L due to removal of water by the Tamarix stands. Despite the high groundwater salinity, the sites away from the river did not have saline surface soils. Only 1% of the mean annual river flow is lost to Tamarix ET on the Lower Colorado River in the United States, and the opportunities for water salvage through Tamarix removal are constrained by its modest ET rates. A possible alternative to Tamarix removal is to intersperse native plants among the stands to improve the habitat value of the riparian zone.

Spatial variability in digenean metacercariae infection of 0-group common sole Solea solea among nurseries along the French Atlantic coast

We sampled 0-group sole juveniles (N = 174) in September and October 2003 in 9 major nurseries located along the French Atlantic coast (English Channel and Bay of Biscay). 0-group sole were infected with 3 genera of digenean metacercariae, Timoniella spp. (Acanthostomidae), Prosorhynchus crucibulum and Prosorhynchus sp. A (Bucephalidae), Podocotyle sp. (Opecoelidae), and an unidentified species of Digenea. Parasite infection levels in the English Channel nurseries were lower, and the community composition was different from Bay of Biscay nurseries. We hypothesize that the difference between geographic areas was due to differences in first intermediate host communities and, to a lesser extent, because of lower temperatures in the English Channel compared to the Bay of Biscay. For the Bay of Biscay nurseries, mean total parasite abundance was strongly negatively correlated with mean annual river flow. This relationship may be the result of the more upstream location of 0-group sole nurseries in estuaries so that fish were further from local points of parasite transmission than those in embayed nurseries. Digenean metacercariae load may be influenced by 3 major local factors, i.e. abundance and proximity of the first intermediate hosts and cercariae dispersal capacities.

Hydrologic impact of climate change in the Saguenay watershed: comparison of downscaling methods and hydrologic models

Changes in global climate will have significant impact on local and regional hydrological regimes, which will in turn affect ecological, social and economical systems. However, climate-change impact studies on hydrologic regime have been relatively rare until recently, mainly because Global Circulation Models, which are widely used to simulate future climate scenarios, do not provide hourly or daily rainfall reliable enough for hydrological modeling. Nevertheless, more reliable rainfall series corresponding to future climate scenarios can be derived from GCM outputs using the so called ‘downscaling techniques’. This study applies two types of statistical (a stochastic and a regression based) downscaling techniques to generate the possible future values of local meteorological variables such as precipitation and temperature in the Chute-du-Diable sub-basin of the Saguenay watershed in northern Québec, Canada. The downscaled data is used as input to two different hydrologic models to simulate the corresponding future flow regime in the catchment. In addition to assessing the relative potential of the downscaling methods, the paper also provides comparative study results of the possible impact of climate change on river flow and total reservoir inflow in the Chute-du-Diable basin. Although the two downscaling techniques do not provide identical results, the time series generated by both methods indicates a general increasing trend in the mean daily temperature values. While the regression based downscaling technique resulted in an increasing trend in the mean and variability of daily precipitation values, such a trend is not obvious in the case of precipitation time series downscaled with the stochastic weather generator. Moreover, the hydrologic impact analysis made with the downscaled precipitation and temperature time series as input to the two hydrological models suggest an overall increasing trend in mean annual river flow and reservoir inflow as well as earlier spring peak flows in the basin.

A Pilot Global Assessment of Environmental Water Requirements and Scarcity

This paper presents a first attempt to estimate the volume of water required for the maintenance of freshwater-dependent ecosystems at the global scale. This total environmental water requirement consists of ecologically relevant low-flow and high-flow components and depends upon the objective of environmental water management. Both components are related to river flow variability and estimated by conceptual rules from discharge time series simulated by the global hydrology model. A water stress indicator is further defined, which shows what proportion of the utilizable water in world river basins is currently withdrawn for direct human use and where this use is in conflict with environmental water requirements. The paper presents an estimate of environmental water requirements for 128 major river basins and drainage regions of the world. It is shown that approximately 20 to 50 percent of the mean annual river flow in different basins needs to be allocated to freshwater-dependent ecosystems to maintain them in fair conditions. This is unlikely to be possible in many developing countries in Asia and North Africa, in parts of Australia, North America, and Europe, where current total direct water withdrawals (primarily for irrigation) already tap into the estimated environmental water requirements. Over 1.4 billion people currently live in river basins with high environmental water stress. This number will increase as water withdrawals grow and if environmental water allocations remain beyond the common practice in river basin management. This paper suggests that estimates of environmental water requirements should be the integral part of global water assessments and projections of global food production.

Climate Change Effects on River Flow to the Baltic Sea

River flow to the Baltic Sea originates under a range of different climate regimes in a drainage basin covering some 1,600,000 km2. Changes to the climate in the Baltic Basin will not only affect the total amount of freshwater flowing into the sea, but also the distribution of the origin of these flows. Using hydrological modeling, the effects of future climate change on river runoff to the Baltic Sea have been analyzed. Four different climate change scenarios from the Swedish Regional Climate Modelling Programme (SWECLIM) were used. The resulting change to total mean annual river flow to the Baltic Sea ranges from -2% to +15% of present-day flow according to the different climate scenarios. The magnitude of changes within different subregions of the basin varies considerably, with the most severe mean annual changes ranging from -30% to +40%. However, common to all of the scenarios evaluated is a general trend of reduced river flow from the south of the Baltic Basin together with increased river flow from the north.

Characterization of the Ebre and Rhone estuaries: A basis for defining and classifying salt‐wedge estuaries

River discharge is the main factor controlling the hydrologic dynamics of the Ebre and Rhone estuaries. The topography of the estuary bed also influences the extent, advance, and retreat of the salt wedge. Tides have little influence because of the low tidal range. Mean annual river discharge is close to the critical value determining the formation and breakup of the salt wedge. This is related to the fact that river flow controls the sedimentary dynamics of the estuary, including the sandbar at the mouth. When discharge is lower than the mean annual river flow, the salt wedge is established and the estuary becomes a depositional environment. With higher flows the salt wedge is washed away and erosive conditions prevail. On the basis of the conditions in which the salt wedge is formed, two types of highly stratified estuaries can be identified. In the first one, a salt‐wedge regime is established during low river flows, whereas during high flows the wedge is washed away and the estuary becomes a river. This circulation pattern corresponds to the “salt‐wedge estuary” or type 4 of the Hansen‐Rattray classification, typical of river‐dominated estuaries in microtidal seas. In the second one, a salt wedge is established during high river flows, whereas a partially mixed estuary occurs during low flows. This pattern corresponds to types 3b and 2b of the Hansen‐Rattray classification.

Behaviour of copper and zinc added to the Tambo River, Australia, by a metal-enriched spring

A study of the behaviour of Cu and Zn added to the upper Tambo River, Australia, by a metal enriched but neutral-pH spring (Wilga Spring) is reported. Approximately 80% of the Cu, Zn, Fe and Mn liberated in the oxidation zone associated with the Wilga orebody is deposited within the groundwater system before the spring water enters the Tambo River. Acidic water from the oxidation zone is neutralized by carbonate-rich groundwater. The input of the spring to the Tambo River, which occurs through the base of the river over a distance of 150-200 m, causes an average sixfold increase in the Cu and Zn concentrations and a measurable increase in the sulfate concentration, but no significant decrease in the pH, in the 'active region' of the river, a distance of approximately 1.3 km. Over the 1-year study period, the spring added an estimated 120 kg of Cu (about 65% in filterable forms) and 230 kg of Zn (about 50% in filterable forms); these fluxes are approximately six times larger than those transported from the upper catchment. The spring also adds an estimated 14.5 t of sulfate, this being roughly the same as the amount (10.7 t) that is transported from the upper catchment. On average, the spring adds only small quantities of Fe and Mn. The concentrations of filterable (or dissolved) Cu and Zn in the 'active region' are largely controlled by adsorption onto iron oxyhydroxide surfaces associated with the particulate matter. At high concentrations of filterable metals, the active surfaces apear to be saturated with Zn and possibly Cu. At river flows in excess of 5-10 ML day-1 (the mean annual river flow is about 22 ML day-1), little Cu and Zn appears to be lost from the water column. The difference in metal concentrations between the 'active region' and Blackfellows Flat (a distance of 10 km) can be explained mostly by dilution of the metal-enriched water in the main branch with water from the southern branch. At low river flows, considerable quantities (up to 99%, depending upon flow) of the Cu, Zn, Fe and Mn added by Wilga Spring are deposited in the 'active region' between the spring and Formfit Creek.