Impact of land-use change on hydrological processes in the Maying River basin, China

Since the 1960s, dramatic changes have taken place in land-use patterns characterized by the persistent expansion of cultivated land and a continuous decrease in natural woodland and grassland in the arid inland river basins of China. It is very important to assess the effects of such land-use changes on the hydrological processes so vital for water resource management and sustainable development on the catchment scale. The Maying River catchment, a typical arid inland watershed located in the middle of the Hexi Corridor in northwest China, was the site chosen to investigate the hydrological responses to land-use changes. The annual runoff, base flow, maximum peak flow, and typical seasonal runoff in both spring and autumn flood periods were selected as the variables in the hydrological processes. Statistical-trend analysis and curvilinear regression were utilized to detect the trends in hydrological variables while eliminating the climatic influence. The relationship between cultivated land-use and hydrological variables was analyzed based on four periods of land-use variation data collected since 1965. A runoff model was established composed of two factors, i.e., cultivated land use and precipitation. The impact of land use changes, especially in the large ar- eas of upstream woodland and grassland turned into cultivated lands since 1967, has resulted in a mean annual runoff decrease of 28.12%, a base flow decline of 35.32%, a drop in the maximum peak discharge of 35.77%, and mean discharge decreases in spring and autumn of 36.05% and 24.87% respectively, of which the contribution of cultivated land expansion to the influence of annual runoff amounts to 77%-80%, with the contribution to the influence of spring discharge being 73%-81%, and that to the influence of base flow reaching 62%-65%. Thus, a rational regulation policy of land use patterns is vitally important to the sustainable use of water resources and the proper development of the entire catchment.     

Assessment of soil erosion and sediment delivery ratio using remote sensing and GIS： a case study of upstream Chaobaihe River catchment, north China

Soil erosion in catchment areas reduces soil productivity and causes a loss of reservoir capacity. Several parametric models have been developed to predict soil erosion at drainage basins, hill slopes and field levels. The well-known Universal Soil Loss Equation （USLE） represents a standardized approach. Miyun reservoir, which sits on Chaobaihe River, is the main surface source of drinking water for Beijing, the capital of China. Water and soil loss are the main reasons for sediment to enter a reservoir. Sediment yield is assessed using a version of the universal soil loss equation modified by Chinese researchers. All year 2001 and 2002 data for factors in the equation are obtained from remote sensing or collected to form an analysis database. These factors are computed and mapped using Geographic Information System tools. Based on the complex database, the modified model is developed. Through pixel-based computing the sediment yield per hydrological unit is calculated. The model does not consider sediment deposition occurring on hillslopes. Gross soil loss is often higher than the sum of those measured at catchment outlets. The sediment delivery ratio （SDR） per hydrological unit is also computed. This study analyzes the main contributions of sediment yields on sub-basins of the Chaobaihe River to the Miyun Reservoir, and discusses the possible reasons for the difference between SDRs in 2001 and 2002 at different outlets. The result shows that in the upper basin of the Miyun Reservoir, in 2001 the area of erosion that could be neglected was 8,202.76 km^2, the area of low erosion 3,269.59 km^2, the area of moderate erosion 3,400.97 km^2, the area of high erosion 436.89 km^2, the area of strong erosion 52.19 km^2 and the area of severe erosion 3.13 km^2. The highest soil loss was 70,353 t/km^2. yr in Fengning County in 2001, followed by 64,418 t/km^2. yr by Chicheng County in 2001. The SDR in 2002 was lower than that in 2001. The main reasons are the decreasing rainfall erosivity and total runoff.     

Impact of the greenhouse effect on sewerage systems—Lund case study

Abstract

The possible impacts of modifications in rainfall patterns due to the greenhouse effect on the function of a sewerage system are studied based on a case study of the city of Lund, Sweden. The Storm Water Management Model is used to simulate changes in the runoff pattern. The paper lists the possible effects of increases in rainfall intensity on the urban water cycle, quantifies changes in the runoff pattern, and discusses the significance of detected changes in terms of economic and environmental consequences and the possibilities to undertake preventative measures. For the purpose of the present study, 10%, 20% and 30% levels of rainfall increase were assumed. In spite of considerable uncertainty regarding the potential future rate of hydrological changes, the examples given of possible impacts of the greenhouse effect on the function of the sewerage system bear witness to the great vulnerability of sewerage systems to the results of climate changes.     

A study of scale effect on specific sediment yield in the Loess Plateau,China

Based on data from 148 hydrometric stations in the Yellow River Basin, an analysis of regional scale relationship, or the relationship between specific sediment yield and drainage basin area, has been undertaken in the study area of the Loess Plateau. For different regions, scale relationship in log-log ordinate can be fitted by two types of lines: straight and parabola, and for each line, a function was fitted using regression analysis. The different scale relationships have been explained in terms of the difference in surface material distribution and landforms. To offset the scale-induced influence, calcu-lation has been done based on the fitted functions, in order to adjust the data of specific sediment yield to a common standard area. Based on the scaled data, a map of specific sediment yield was con-structed using Kriging interpolation. For comparison, a map based on the un-scaled data of specific sediment yield was also constructed using the same method. The two maps show that the basic pattern of specific sediment yield was basically the same. The severely eroded areas (Ys >10000 t km-2a-1) were at the same locations from Hekouzhen to Longmen in the middle Yellow River Basin. However, after the adjustment to a common standard area, the very severely eroded area (Ys >20000 t km-2a-1) became much enlarged because after the adjustment, all the values of Ys in the lower river basin in those regions became much larger than before.     

Scenarios of the spread of a waste heat discharge in a river — Vistula River case study

The problem of two-dimensional mathematical modelling of heated cooling water discharges into running waters is considered in the paper. Two models — one for the evaluation of 2D turbulent velocity field and the other, developed by authors of the study, for 2D heat transport in open-channels — were used in the calculations. Relevant scenarios of the spread of heated water discharged from a designed gas-stem power plant to be constructed at the Vistula River were presented. Environmentally most friendly variant of the discharge of the thermal pollution was selected from among four various variants.     

Impacts of massive pumping on flood processes in polders—with a case study on Lannihu basin in the Dongting Lake District,China

Flooding risk in polders is dictated by not only rainfall, topography, and land use, but also massive pumping. Unfortunately, existing models are inadequate for resolving floods as water transfer due to pumping is insufficiently accounted for. Here an improved hydrological model (MGB-MP) is proposed under the framework of the large-scale hydrological model (MGB) based on the principle of water balance, explicitly incorporating massive pumping within a polder and also out to external rivers. The proposed model is calibrated and validated for the Lannihu basin, a typical polder with an area of 1353 km² and 126 pumping stations in the Dongting Lake District, China and surrounded by Xiangjiang River and Zishui River. The model performs fairly well, with Nash-Sutcliffe efficiencies concerning water levels over 0.76 for the calibration and over 0.73 for the validation. The model is applied to the Lannihu basin under different pumping station settings and rainfall scenarios to unravel how and to what extent massive pumping affects the flood processes as characterized by water levels and discharge hydrographs. It is shown that massive pumping considerably alters the discharge hydrographs and accordingly leads to substantial decrease in the water levels of rivers, which are independent unit-polders, due to water transfer between unit-polders within the basin and out of the basin. The closer the unit-polders are to pumping stations, the more the water levels in unit-polders decrease. The water levels in unit-polders away from a pumping station is affected by the pumping station capacity to a greater extent than the pumping station's threshold water level for initiating pumping.     

Greener rivers in a changing climate?—Effects of climate and hydrological regime on benthic algal assemblages in pristine streams

Excessive biomass development of benthic algae is often considered undesirable, but understanding the causes is confounded by complex interactions among driving factors. Pristine rivers allow a benchmark where human interference should be limited to climate change. In this study a time series comprising >20 years of annual benthic algae surveys from two pristine, soft water, boreal stream sites is used to determine whether year-to-year variations in benthic algal assemblages and cover were related to climate (temperature, precipitation, North Atlantic Oscillation) or hydrological regime. Total benthic algal cover ranged from 6 to 100% at Atna (the outflow of the Atna River from Lake Atnasjø), and from 3 to 50% at the headwater stream Li. Climate and hydrological regime explained 18 - 74% of the variability in benthic algal assemblages and cover. Generally, more variance was explained at Li than at Atna, possibly because (i) aquatic bryophytes blurred nutrient-mediated effects of climate and hydrology at Atna, and (ii) the upstream lake buffered hydrological variation. Temperature was more important for explaining benthic algal assemblages and cover at Atna, while hydrology was more important at Li. Climate and hydrological regime had no major impact on benthic algal taxon richness. High temperatures were associated with high benthic algal cover, particularly at Atna, while high suspended particle concentrations were associated with reduced benthic algal cover at Li, possibly due to scouring. Cover of the cyanobacterium Phormidium sp. increased at Li with increasing temperature, and decreased with prolonged periods of high discharge. Current predictions of climate change would lead to a “greener” Atna (increased cover of benthic algae), while Li would become more “bluegreen” (more Phormidium sp. but less filamentous green algae). It would also lead to a slightly more “eutrophic” algal assemblage at Atna (as indicated by the PIT-index for ecological status assessment), while a possible drift of the PIT-index is less clear at Li. The differences between Atna and Li likely reflect differences among river types, and it seems possible to make some generalizations: climate will likely affect benthic algae in lake outlets primarily via temperature, while headwater streams will primarily be affected via altered hydrology and particle concentrations.     

Influences of retrogressive erosion of reservoir on sedimentation of its downstream river channel——A case study on Sanmenxia Reservoir and the Lower Yellow River

Retrogressive erosion, a widespread phenomenon of sediment transport in reservoirs, often impacts on both the reservoir capacity and the sedimentation in the downstream river channel. Based on field data from the Sanmenxia Reservoir and the Lower Yellow River over the past decades, three courses of ret-rogressive erosion with distinctive features were analyzed. The results indicate that retrogressive erosion, especially caused by rapid reduction in the water level till the reservoir is empty, often results in the serious siltation of the lower Yellow River and threatens the safety of the flood control in the Lower Yellow River. Unreasonable operation of the reservoir and incoming hyperconcentrated floods accom-panied by retrogressive erosion also aggravate the siltation of the main channel of the river. However, a reasonable operation mode of the reservoir so named"storing the clear (low sediment concentration) water in the non–flood season, and sluicing the muddy(high sediment concentration) water in the flood season" was found, which might mitigate the deposition in both the reservoir and the Lower Yellow River. This operation mode provides important experience for the design and operation of large reser-voirs in other large rivers carrying huge amounts of sediment.     

Assessment of sediment yield estimations for large watershed areas: a case study for the Seyhan,Demirköprü and Hirfanlı reservoirs in Turkey

Abstract

Analyses of data from reservoir surveys and sediment rating curves are compared to predict sediment yield in three large reservoir watershed areas in Turkey. Sediment yield data were derived from reservoir sedimentation rates and suspended sediment measurements at gauging stations. The survey data were analysed to provide the volume estimates of sediment, the time-averaged sediment deposition rates, the long-term average annual loss rates in the reservoir storage capacity, and the long-term sediment yield of the corresponding watershed areas. Four regression methods, including linear and nonlinear cases, were applied to rating curves obtained from gauging stations. Application of the efficiency test to a power function form of a rating curve with nonlinear regression yielded the highest efficiency values. Based on the analysis of the sediment rating curves, sediment load fluxes were calculated by using average daily discharge data at each gauging station. Comparison of these two sediment yield values for each reservoir showed that the sediment yields from the suspended sediment measurements, SY_GS, are 0.99 to 3.54 times less than those obtained from the reservoir surveys, SY_RS. The results from the reservoir surveys indicate that all three reservoirs investigated have lost significant storage capacity due to high sedimentation rates.     

Long-term stable water isotope and runoff data for the investigation of deforestation effects on the hydrological system of the Wüstebach catchment,Germany

The Wüstebach catchment belongs to the German TERENO (Terrestrial Environmental Observatories) network and was partially deforested (~21%) by the Eifel National Park in 2013. In this data paper, we provide 11-year precipitation and stream water isotope data and the corresponding runoff discharge rates recorded in the Wüstebach catchment (from 2009 to 2019). In addition, we provide an overview of available datasets and access information for environmental data of the Wüstebach catchment that are discoverable with associated metadata at the Web-based TERENO data portal. We anticipate that this comprehensive data set will give new insights in how deforestation influences the hydrological system, for exampole, in terms of transit time distribution, fraction of young water and water flow paths at the catchment scale.     

Impact of warming climate on water management for the Ariège River basin (France)

Abstract

The French national project IMAGINE2030 aims to assess future water availability in the Garonne River basin (southwest France) by taking account of changes in both climate and water management in the 2030s. Within this project, two mountainous drainage basins located in the Pyrenees were examined to assess the specific impact of climate change on reservoir management. The Salat River basin at Roquefort, is considered as a proxy (representative of a natural basin), whereas the Ariège River at Foix is influenced by hydropower production in winter and by water releases to sustain low flows in summer. The Cequeau rainfall–runoff model, combined with a simplified model of reservoir management operations, was calibrated on present-day conditions and forced with climate projections derived from the IPCC AR4 report. The results show that a warming climate over the basins induces a decrease in mean annual runoff, a shift to earlier snow melting in mountainous areas and more severe low-flow conditions. The simulations show a decrease in electricity generation. Under two water management scenarios (one “business-as-usual” and the other incorporating an increased downstream water demand in compliance with requirements for increased minimum flow), simulations for the Ariège River basin suggest an earlier filling of the reservoir is necessary in winter to anticipate the increased release from reservoirs in summer to support minimum flow farther downstream.

Editor Z.W. Kundzewicz; Associate editor D. Hughes

Citation Hendrickx, F. and Sauquet, E., 2013. Impact of warming climate on water management for the Ariège River basin (France). Hydrological Sciences Journal, 58 (5), 976–993.     

Effect of sediment resuspension on underwater light field in shallow lakes in the middle and lower reaches of the Yangtze River: A case study in Longgan Lake and Taihu Lake

Based on three continuous in situ underwater light field measurement under different wind waves conditions in Longgan Lake, Meiliang Bay of Taihu Lake in July 2003 and littoral zone near TLLER in July 2004, respectively, the effects of sediment resuspension caused by wind waves on PAR diffuse attenuation, absorption coefficients and euphotic depths are analyzed. In Longgan Lake, PAR diffuse attenuation coefficients during small, middle and large wind waves were 1.74, 2.02 and 2.45 m-1, respectively, and the corresponding PAR spectral diffuse attenuations ranged from 0.98 to 2.97, 1.34 to 3.95 and 1.80 to 5.40 m-1, respectively. In Meiliang Bay, PAR diffuse attenuation coefficients were 2.63, 3.72, 4.37 m-1 during small, middle and large wind waves. PAR diffuse attenuation coefficients increased by 41% and 66% from small to middle, large wind waves, respectively. Absorption coefficients integrated over the range of PAR of CDOM, phytoplankton were 0.26, 0.28 m-1; 0.76, 0.49 m-1, respectively during middle and large wind waves. Absorption coefficients integrated over the range of PAR of non-algal particulate matter and total suspended particulate matter increased from 0.94 to 1.73 m-1, and from 1.70 to 2.22 m-1, respectively during middle and large wind waves. Relative contributions of absorption coefficients of non-algal particulate matter to total absorption coefficient integrated over the range of PAR were 44.14%, 65.05%, respectively, during middle and large wind waves. PAR euphotic depths decreased by 0.40, 0.19, 0.20 m from middle to large wind waves in Longganhu Lake, Meliang Bay and littoral zone near TLLER. Significant correlations were found between transparency, PAR diffuse attenuation coefficients, euphotic depths and total suspended paniculate matter, wind velocity, wave height. Most significant correlations were found between transparency, PAR diffuse attenuation coefficients, euphotic depths and inorganic suspended paniculate matter but low correlations for chlorophyll a, dissolved organic carbon. Increase of total suspended paniculate matter, especially inorganic suspended paniculate matter caused by wind waves was the dominant factor affecting underwater light field in shallow lakes in the middle and lower reaches of the Yangtze River based on observations at three stations.     

Hydrochemical characteristics and water quality of the Mušnica River catchment,Bosnia and Herzegovina

Abstract

The spatial position of the Mu?nica River catchment in the Dinaric Karst results in specific conditions of the drainage, distribution and chemical characteristics of the surface water and groundwater. This catchment is mountainous, located between 930 and 1985 m above sea level. The chemical characteristics of the waters are strongly dependent on the local lithological composition and the precipitation regime. The dominant cations are Ca²⁺ and Mg²⁺, and anions HCO₃ ^- and SO₄ ^2-. The surface water is characterized by low and medium mineralization, with resultant soft, medium-hard and very-hard total hardness levels. The groundwater is more mineralized than the surface water. Gacko Town and its associated thermal power plant, Gacko 1, which are located in the southern part of the Mu?nica River catchment, have no modern facilities for sewage and wastewater transport or treatment. In order to prevent further water quality deterioration and to enable its sustainable use, it is recommended to ensure adequate protection measures in the catchment area.

Editor Z.W. Kundzewicz; Associate editor S. Faye

Citation Banjak, D. and Nikoli?, J., 2012. Hydrochemical characteristics and water quality of the Mu?nica River catchment, Bosnia and Herzegovina. Hydrological Sciences Journal, 57 (3), 562–575.     

Flood events and flood risk assessment in relation to climate and land-use changes: Saint-François River,southern Québec,Canada

Abstract

In the current context of climatic variability, it is important to quantify the impact on the environment. This study deals with an analysis of climatic data and land-use changes in terms of the impacts on flood recurrence based on multisource data. The study area covers the mouth of the Saint-François River (southern Québec, Canada), where spring floods and ice jams are a recurring problem. The flood frequency analysis shows an increase in flooding over recent decades, attributable to an increase in winter temperatures that has the effect of causing ice jams earlier in the year. Regarding land-use changes, a small decrease in agricultural surface areas is observed, from 53% to 39%, along with increases in forest and urban surface areas from 27% to 38% (forest) and 3% to 5% (urban) between 1928 and 2005. In a context of continuing climate warming, more pronounced inter-annual variations are to be expected along with a higher incidence of flooding.

Editor Z.W. Kundzewicz

Citation Ouellet, C., Saint-Laurent, D. and Normand, F., 2012. Flood events and flood risk assessment in relation to climate and land-use changes: Saint-François River, southern Québec, Canada. Hydrological Sciences Journal, 57 (2), 313–325.     

Impact of ocean–wave coupling on typhoon-induced waves and surge levels around the Korean Peninsula: a case study of Typhoon Bolaven

Typhoon-induced waves and surges are important when predicting potential hazards near coastal regions. In this paper, we applied a coupled modeling system for ocean–wave interaction to examine prediction capabilities for typhoon-induced waves and surges around the Korean Peninsula. To identify how ocean–wave coupling impacts wave and surge simulations during typhoon conditions, a set of comparative experiments was performed during Typhoon Bolaven (2012): (1) a fully coupled ocean–wave model, (2) a one-way coupled ocean–wave model without surface current feedback and ocean-to-wave water levels, and (3) a stand-alone ocean model without considering wave-based sea surface roughness (SSR). When coupled with the ocean model, the surface current reduced significantly the wave height on the right-hand side of the advancing typhoon track and improved prediction accuracy along the southern coast of Korea. Compared with the observed surge levels, the simulated surge height yielded improved results for peak height magnitude and timing compared with the uncoupled model. For wave-to-surge feedback, we found that wave-induced SSR plays an important role by modulating wind stress in the surface layer. The modulated wind stress directly affected the surge height, which improved surge peak prediction during the typhoon.     

Experimental study on the effect of bottomless structure in front of a bottom outlet on a sediment ?ushing cone

One of the main problems in reservoirs is sedimentation which reduces the operating life of dams if a proper plan and analysis method are not in place.The techniques to manage sediment in reservoirs include several sustainable management techniques that route sediment through or around the reservoir.One of the main economical methods in arid and semi-arid regions is pressurized flushing using moderate drawdown of the water level of the reservoir to evacuate sediment deposited behind dams.In the current study,the effect of a new structure called a dendritic bottomless extended (DBE) outlet structure at three angles of 30°,45°,and 60° on pressurized flushing efficiency was investigated.Consequently,45 experiments were designed for three discharge rates (Q_o) ,three sediment levels (H_s),four types of structure,and a no-structure condition (reference test).The results indicated that the DBE structure with a 30° angle between the branches,a sedimentary dimensionless index of ■,and a flow dimensionless index of ■(where g is the acceleration of gravity and Do is the diameter of the bottom outlet) lead to 10-fold increase in the sediment flushing cone dimensions and sediment removal efficiency compared to the results of the reference test.Finally,according to a statistical analysis of the results,a dimensionless equation for calculating the sediment flushing cone dimensions was developed for the tested sediment characteristics.     

Changes in the plain river system and its hydrological characteristics under urbanization – case study of Suzhou City,China

ABSTRACT

Rapid urbanization in China has severely disturbed the underlying surface and river systems. The stream structure parameters of Suzhou City were analysed to study the evolution and spatial differentiation of a water system undergoing urbanization. The influencing pattern of different urbanization processes on river system structure and hydrological processes was detected by statistical methods and simulation analysis. The results show that urban sprawl is influenced by both the natural environment and the social economy. At different stages of urbanization, the spatial urban expansion and the natural river characteristics influence the evolution of the river network: during rapid urbanization, the decline in surface water ratio and river density is more intense. The decrease of surface water ratio and river density in rapidly urbanized areas was greatest, followed by that in area urbanized in the 1980s, with few changes in the old town. Under high urbanization, river system indicators tend to stabilize. The rivers’ hydrological features were affected by urbanization, with water yield in the study area increasing from 0.81 to 0.95 m³/m² (1991–2015). The same rainfall intensity results in higher flood levels and greater risk of flooding under rapid urbanization.     

Erosion and aggradation on persistently active volcanoes—a case study from Semeru Volcano,Indonesia

Erosion processes on active volcanoes in humid climates result in some of the highest sediment yields on Earth. Episodic sediment yields after large eruptions have been evaluated, but not the long-term and continuous patterns on persistently active volcanoes. We have used high-spatial resolution satellite imagery and DEMs/DSMs along with field-based geologic mapping to assess accurately sediment budgets for the active Semeru Volcano in Java, Indonesia. Patterns of aggradation and degradation on Semeru differ from that of other active volcanoes because (1) both episodic pyroclastic density currents (PDC) and continuous supplies of tephra generate pulses of sediment, (2) sediment is transferred via cycles of aggradation and degradation that continue for >15 years in river channels after each PDC-producing eruption, and (3) rain-triggered lahars remove much greater material than fluvial transport during long, intense rainfall events. The geomorphic response of two of Semeru’s rivers to volcanic sediment migration indicates that (1) each river experiences alternating aggradation and degradation cycles following PDC-producing eruptions and (2) spatial patterns of sediment transfer are governed by geomorphic characteristics of the river reaches. Usually high degradation in the steep source reach is followed by a long bypassing middle reach. Aggradation predominates in the depositional reaches further down valley on the ring plain. Average sediment yields (10³–10⁵ t/km²/year) at persistently active volcanoes are two to three orders of magnitude lower than sediment yields after large and infrequent eruptions, but the continuous and steady sediment transfer in rivers removes more sediment on a mid-term (10 years) to long-term (30 years) basis. In contrast to the trend observed on composite cones after large and infrequent eruptions, decay of sediment yields is not exponential and river channels do not fully recover at steadily active volcanoes as episodic inputs from BAF eruptions, superimposed on the background remobilization of daily tephra, have a greater cumulative effect.