Floodplain hydrology of the Mekong Delta,Vietnam

The Mekong Delta is one of the largest and most intensively used estuaries in the world. Each year it witnesses widespread flooding which is both the basis of the livelihood for more than 17 million people but also the major hazard. Therefore, a thorough understanding of the hydrologic and hydraulic features is urgently required for various planning purposes. While the general causes and characteristics of the annual floods are understood, the inundation dynamics in the floodplains in Vietnam which are highly controlled by dikes and other control structures have not been investigated in depth. Especially, quantitative analyses are lacking, mainly due to scarce data about the inundation processes in the floodplains. Therefore, a comprehensive monitoring scheme for channel and floodplain inundation was established in a study area in the Plain of Reeds in the northeastern part of the Vietnamese Delta. This in situ data collection was complemented by a series of high‐resolution inundation maps derived from the TerraSAR‐X satellite for the flood seasons 2008 and 2009. Hence, the inundation dynamics in the channels and floodplains, and the interaction between channels and floodplains, could be quantified for the first time. The study identifies the strong human interference which is governed by flood protection levels, cropping patterns and communal water management. In addition, we examine the tidal influence on the inundation in various parts of the Delta, since it is expected that climate change‐induced sea level rise will increase the tidal contribution to floodplain inundation. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis and attribution of trends in water levels in the Vietnamese Mekong Delta

In the Vietnamese Mekong Delta (VMD), water levels at some stations have increased. However, the factors that cause this rise in the VMD have not been identified. We considered four factors that may have contributed to the water level rise: (1) increased runoff from upstream, (2) sea‐level rise, (3) land subsidence, and (4) decrease in flood mitigation function because of construction of high dykes. We analysed daily maximum and minimum water levels, and mean daily water levels from 24 monitoring stations from 1987 to 2006. Using daily and annual water level differences, we classified the delta into two groups: one is dominated by flows from upstream, while the other is tide dominated. We then tested the trends of annual maximum and minimum water levels using the Mann–Kendall test, and identified the slope of the trend using the method of Sen. The areas of dyke construction were estimated using the Enhanced Vegetation Index (EVI) and Land Surface Water Index (LSWI) from the Moderate Resolution Imaging Spectroradiometer (MODIS) data. Results show (1) river inflow has little impact on rising water levels in the VMD, (2) the influence of high dykes on water level rise could not be quantified in this study, and (3) both maximum and minimum water levels significantly increased in the tide‐dominated area. Trend of annual minimum water level can be considered as the sum sea‐level rise and land subsidence. Therefore, we attribute 6.05 mm year^?1 (80%) to land subsidence and 1.42 mm year^?1 (20%) to sea level rise, indicating that inundations have been severe in the VMD, caused primarily by land subsidence. Copyright © 2015 John Wiley & Sons, Ltd.     

Sedimentation in the floodplains of the Mekong Delta,Vietnam. Part I: suspended sediment dynamics

Suspended sediment is the primary source for a sustainable agro‐ecosystem in the Mekong Delta by providing nutrient input for the subsequent cropping season. In addition, the suspended sediment concentration (SSC) plays an important role in the erosion and deposition processes in the Delta; that is, it influences the morphologic development and may counteract the deltaic subsidence and sea level rise. Despite this importance, little is known about the dynamics of suspended sediment in the floodplains of the Mekong Delta. In particular, quantitative analyses are lacking mainly because of data scarcity with respect to the inundation processes in the floodplains. In 2008, therefore, a comprehensive in situ system to monitor the dynamics of suspended sediment in a study area located in the Plain of Reeds was established, aiming at the characterization and quantification of suspended sediment dynamics in the deeply inundated parts of the Vietnamese part of the Mekong Delta. The monitoring system was equipped with seven water quality–monitoring stations. They have a robust design and autonomous power supply suitable for operation on inundated floodplains, enabling the collection of reliable data over a long period of time with a high temporal resolution. The data analysis shows that the general seasonal dynamics of suspended sediment transport in the Delta is controlled by two main mechanisms: the flood wave of the Mekong River and the tidal backwater influences from the coast. In the channel network, SSC decreases exponentially with distance from the Mekong River. The anthropogenic influence on SSC could also be identified for two periods: at the start of the floodplain inundation and at the end of the flood period, when subsequent paddy rice crops are prepared. Based on the results, we recommend an operation scheme for the sluice gates, which intends to distribute the sediment and thus the nutrients equally over the floodplain. Copyright © 2013 John Wiley & Sons, Ltd.     

Dynamics of a fringe mangrove forest detected by Landsat images in the Mekong River Delta,Vietnam

Mangrove forests dominate many tropical coastlines and are one of the most bio‐diverse and productive environments on Earth. However, little is known of the large‐scale dynamics of mangrove canopies and how they colonize intertidal areas. Here we focus on a fringe mangrove forest located in the Mekong River Delta, Vietnam; a fast prograding shoreline where mangroves are encroaching tidal flats. The spatial and temporal evolution of the mangrove canopy is studied using a time series of Landsat images spanning two decades as well as Shuttle Radar Topography Mission (SRTM) elevation data. Our results show that fast mangrove expansion is followed by an increase in Normalized Difference Vegetation Index (NDVI) in the newly established canopy. We observe three different dynamics of the mangrove fringe: in the southwest part of the fringe, near a deltaic distributary where the fringe boundary is linear, the canopy expands uniformly on the tidal flats with a high colonization rate and high NDVI values. In the northeast part of the fringe, near another distributary, the canopy expands at a much lower rate with low NDVI values. In the fringe center, far from the river mouths, the fringe boundary is highly irregular and mangroves expansion in characterized by sparse vegetated patches displaying low NDVI values. We ascribe these different dynamics to wave action and southwest longshore transport triggered by energetic northeasterly monsoons during winter. We further link the large‐scale dynamics of the fringe to small‐scale physical disturbances (waves, erosion and deposition) that might prevent the establishment of mangrove seedlings. Based on these results, we include mangrove encroachment in an already published conceptual model of progradation of the Mekong River Delta. We conclude that high NDVI values and a constantly linear vegetation–water interface are indicative of stable mangrove canopies undergoing fast expansion, probably triggered by sediment availability at the shore. Our results can be applied more generally to mangrove forests growing in minerogenic and high tidal range environments with high sediment inputs. Copyright © 2016 John Wiley & Sons, Ltd.     

Changes in hydrology and sediment delivery of the Mekong River in the last 50 years: connection to damming,monsoon, and ENSO

As the population and economy boom, more and more dams are being built in the Mekong River basin. Previous studies have revealed that Manwan Dam had little influence on the runoff–SSC (suspended sediment concentration) relationship, and the sediment load was relatively stable over the past 40 years. However, little is known at present on the relationship among monsoons, El Niño Southern Oscillation (ENSO), precipitation, runoff, and the impact of dams on the delta dynamics. A comprehensive hydropower GIS database covering the entire Mekong basin is presented in this study. Mann–Kendall trend analysis showed no significant change in precipitation and runoff over the past 50 years. Spectral analysis showed that the runoffs of the middle to lower reach of Mekong River are correlated with the Indian Monsoon, where as the East Asian Monsoon's influence is mainly on the lower reach. With another 200 new dams to be added to the basin in the next couple of decades, changes are expected in both hydrological regime and delta dynamics. On one hand, the runoff showed a closer connection with the regional precipitation and ENSO in the post‐dam period (1993–2005) than in the pre‐dam period (1950–1993). Such a relationship is expected to be even closer when more dams are completed. On the other hand, both daily maximum and minimum water levels on the delta plain have shown an abrupt drop since the end of 1994. This reduced water‐level gradient between the river and sea inevitably weakens the sediment discharge to the coast, which might intensify the ongoing coastal erosion on the eastern part of the delta plain. Copyright © 2010 John Wiley & Sons, Ltd.     

River Discharge and Water Level Changes in the Mekong River: Droughts in an Era of Mega-Dams

While 1992 marked the first major dam – Manwan – on the main stem of the Mekong River, the post-2010 era has seen the construction and operationalisation of mega dams such as Xiaowan (started operations in 2010) and Nuozhadu (started operations in 2014) that were much larger than any dams built before. The scale of these projects implies that their operations will likely have significant ecological and hydrological impacts from the Upper Mekong Basin to the Vietnamese Delta and beyond. Historical water level and water discharge data from 1960 to 2020 were analysed to examine the changes to streamflow conditions across three time periods: 1960–1991 (pre-dam), 1992–2009 (growth) and 2010–2020 (mega-dam). At Chiang Saen, the nearest station to the China border, monthly water discharge in the mega-dam period has increased by up to 98% during the dry season and decreased up as much as −35% during the wet season when compared to pre-dam records. Similarly, monthly water levels also rose by up to +1.16 m during the dry season and dropped by up to −1.55 m during the wet season. This pattern of hydrological alterations is observed further downstream to at least Stung Treng (Cambodia) in our study, showing that Mekong streamflow characteristics have shifted substantially in the post-2010 era. In light of such changes, the 2019–2020 drought – the most severe one in the recent history in the Lower Mekong Basin – was a consequent of constructed dams reducing the amount of water during the wet season. This reduction of water was exacerbated by the decreased monsoon precipitation in 2019. Concurrently, the untimely operationalisation of the newly opened Xayaburi dam in Laos coincided with the peak of the 2019–2020 drought and could have aggravated the dry conditions downstream. Thus, the mega-dam era (post-2010) may signal the start of a new normal of wet-season droughts.     

River adjustments in response to human activities: A case study of the lower Beijiang River,China

Intensive human activity has caused significant changes in the river morphology and hydrological characteristics of the Pearl River Delta. Particularly, in-channel mining and dam construction have induced remarkable levels of downward riverbed incision. Although strict control measures have been implemented for in-channel sand mining, it remains unclear how the river has evolved since the abandonment of high-intensity mining and its impact on flow diversion at the downstream confluence. This study presents the hydrological and morphological adjustments in the lower Beijiang River, the second largest tributary of the Pearl River, under the impacts of human interventions. A hydrodynamic model was developed to reveal the impacts of riverbed deformation on the flow diversion ratio at Sixianjiao, the confluence of the Beijaing River and the Xijiang River. The results showed that construction of cascade reservoirs upstream reach did not strongly influence run-off, whereas incoming sediment loads were decreased. Because of upstream damming and in-channel sand mining, a dramatic downward incision was observed in the lower Beijiang River, with a degradation volume of approximately 239.8 million m³ from 1999 to 2012. Particularly, in the upper reach, the incision depth was typically larger than 8 m. Riverbed incision caused continuous changes in the water stage–discharge relationship, and discharge increased remarkably under the same water level at the three hydrometric stations. During 2012–2020, because in-channel sand mining was strictly controlled, rapid degradation was alleviated, deposition occurred in some cross-sections and the deformation volume decreased by approximately 90% compared to that in the last period. A fast downward incision induced a change in flow exchange between the two rivers, and the flow diversion ratio of the Beijiang River increased from an average of 17% before 1998 to more than 21%.     

Impact of beaver dam analogues on hydrology in a semi-arid floodplain

Natural beaver ponds help connect the stream to the floodplain, maintain late summer low flows and reduce peak flow during high flow events by offering temporary surface water (SW) storage. When beavers are extirpated from the landscape, stream degradation often ensues. This study assesses the impact of beaver dam analogues (BDA) as a stream restoration technique to help maintain low flow water levels and enhance stream-floodplain interactions on a seasonal basis in Red Canyon Creek, Lander, WY. BDAs increased SW and groundwater (GW) levels, favoured the occurrence of flow reversals (i.e., stream-to-floodplain GW flow) during high flow events associated with mid-winter and early-spring thaw events, and reduced the groundwater-to-stream hydraulic gradient on an annual basis. Although GW temperatures varied seasonally, relatively cooler GW temperatures were observed in the BDA impacted reach compared to the control reach away from BDA influence. BDAs however did not significantly impact stream temperatures. Overall, results suggest that when installed in sequence, BDA complexes can successfully reconnect the stream to its floodplain, and ultimately increase SW-GW exchange at the floodplain scale by allowing flow reversals to occur and by reducing the GW to stream hydraulic gradient. Although BDAs built with fence posts, willow branches, sediments and small boulders are naturally porous and require regular maintenance, this study also highlights the viability of small BDAs as a restoration practice to enhance landscape resilience to drought and high flow events in deeply incised channels where beavers would not come back naturally.     

Development of a flood water level estimation method using satellite images and a digital elevation model for the Mekong floodplain

We have developed a flood water level estimation method that only employs satellite images and a DEM. The method involves three steps: (1) discriminating flood areas and identifying clumps of each flood area, (2) extracting the edges of the identified flood area using a buffering technique, and (3) performing spatial interpolation to transform the extracted elevation to flood water levels. We compared the estimated flood water levels with the observed ones. The RMSE using the RADARSAT was 1.99 and 1.30 m at river and floodplain points, respectively, whereas the RMSE using the MODIS was 4.33 and 1.33 m at the river and floodplain points, respectively. Given that most errors are attributed to the DEM, the method exhibited good performance. Furthermore, the method reproduced the flow directions and flood water level changes during the flooding period. Thus, we demonstrated that the characteristics of flood inundation can be understood even when ground observation data cannot be obtained.     

Spatial assessment of hydrologic alteration across the Pearl River Delta,China, and possible underlying causes

The alterations of the water level across the Pearl River Delta (PRD) were investigated using a ‘range of variability approach’ (RVA) based on monthly water level datasets extracted from 17 gauging stations. A mapping method was used to illustrate the spatial patterns in the degrees of alteration of water levels. The results indicated that more stations showing moderate and high alterations in monthly mean maximum and minimum water levels when compared with monthly maximum and minimum water levels. River channels characterized by higher alterations of water levels were observed mainly in the regions north of 22° 30′N. Alterations of water levels across the PRD were a consequence of various influencing factors. However, changed hypsography due to extensive and intensive human activities, particularly the large‐scale dredging and excavation of the river sand, may be taken as one of the major causes for the substantial hydrologic alteration. This study indicated that the river channels characterized by altered water levels are mostly those characterized by highly and moderately intensive sand dredging. The changed ratio of the streamflow between Makou and Sanshui stations, the major upstream flow control stations, also influenced the water level alterations of the Pearl River delta. The results of this study will be of great significance in water resources management and better human mitigation of the natural hazards due to the altered water level under the changing environment. Copyright © 2009 John Wiley & Sons, Ltd.     

三门峡水库冲淤重心变化及其对潼关高程的影响

以往关于三门峡水库的研究多关注库区年际间的冲淤变化,而对汛期和非汛期库区冲淤分布研究较少。本文基于三门峡水库蓄清排浑运用以来1974 2018年实测水沙、断面及冲淤数据,研究汛期和非汛期库区冲淤重心的迁移、冲淤速率及其对潼关高程的影响。结果表明,蓄清排浑运用以来库区河道基本遵循汛期冲刷、非汛期淤积的演变规律。分别定义汛期最大冲刷速率和非汛期最大淤积速率发生的相邻两断面间的子河段为冲刷重心和淤积重心,汛期冲刷重心与非汛期淤积重心出现的位置基本对应,1974 2010年冲淤重心由距坝约90 km逐渐向坝前移动,平均下移速率约1～2km/a;2010年后冲淤重心逐渐上移,2017年位于坝上游约60～70 km,但冲淤强度明显减弱。淤积重心的位置主要受水库回水长度影响,冲刷重心主要与汛期水流能量相关,淤积重心位置迁移滞后于影响因子的变化约5年,而冲刷重心滞后时间约2年。潼关高程与潼关至太安段（潼太段）比降呈反比关系,比降越大,潼关高程越低,而当冲刷重心迁移至潼太段并影响其下段时,潼太段比降增大,利于潼关高程降低。1985年后回水范围和冲淤重心均位于潼关以下,潼关高程受冲淤重心影响较小。     

Geomorphic evolution of the Qingshuigou channel of the Yellow River Delta in response to changing water and sediment regimes and human interventions

Delta channels are important landforms at the interface of sediment transfer from terrestrial to oceanic realms and affect large, and often vulnerable, human populations. Understanding these dynamics is pressing because delta processes are sensitive to climate change and human activity via adjustments in, for example, mean sea level and water/sediment regimes. Data collected over a 40-year period along a 110-km distributary channel of the Yellow River Delta offer an ideal opportunity to investigate morphological responses to changing water and sediment regimes and intensive human activity. Complementary data from the delta front provide an opportunity to explore the interaction between delta channel geomorphology and delta-front erosion–accretion patterns. Cross-section dimensions and shape, longitudinal gradation and a sediment budget are used to quantify spatial and temporal morphological change along the Qingshuigou channel. Distinctive periods of channel change are identified, and analysis provides a detailed understanding of the temporal and spatial adjustments of the channel to specific human interventions, including two artificial channel diversions and changes in water and sediment supply driven by river management, and downstream delta-front development. Adjustments to the diversions included a short-lived period of erosion upstream and significant erosion in the newly activated channel, which progressed downstream. Channel geomorphology widened and deepened during periods when management increased water yield and decreased sediment supply, and narrowed and shallowed during periods when management reduced water yield and the sediment load. Changes along the channel are driven by both upstream and downstream forcing. Finally, there is some evidence that changing delta-front erosion–accretion patterns played an important role in the geomorphic evolution of the deltaic channel; an area that requires further investigation. © 2020 John Wiley & Sons, Ltd.     

Basic data on the hydrology of Lakes Ohrid and Prespa

This paper deals with hydrological analyses of Lakes Ohrid and Prespa. The watersheds and the lakes themselves are shared by three countries: Albania, Greece and Macedonia. As a result of insufficient interstate scientific cooperation and inexistence of data exchange, the lakes and their watersheds are not fully investigated regarding hydrology and hydrogeology. This paper represents a first attempt at a complete hydrological analysis based on data from the Macedonian side. This is not considered to be a particular deficiency, because over 60% of the lakes' watersheds and the lakes themselves belong to Macedonia, where a great number of reliable and long‐term data series of hydrometeorological observations exist. The Prespa lakes do not have surface outflow and are connected with Lake Ohrid by underground karst conduits. Because of this, from the hydrological point of view, the lakes and their watersheds cannot be analysed separately. The changes of the regime of the air temperature and the rainfall distribution have been investigated in this report. An increase of the maximum and decrease of the minimum annual air temperatures, as well as a decrease of annual precipitation sums has been determined. Also, a statistically significant descending trend of water level in both lakes has been confirmed, with a statement that the water level decrease in Lake Prespa is extremely alarming. From 1985 to 1995 the water level in Lake Prespa has dropped by more than 5 m. The main reasons for this cannot be identified easily because there are no data on water use quantities from all three countries. As the lakes represent unique natural, ecological and economical water resources in a region suffering water shortage, we plead for a strengthening of international support in activities on salvation of both lakes. A prerequisite for this is the water balance calculation and common cooperation in sustainable water resources management of the lakes. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of climate change on sea water intrusion in coastal aquifers

There is increasing debate these days on climate change and its possible consequences. Much of this debate has focused in the context of surface water systems. In many arid areas of the world, rainfall is scarce and so is surface runoff. These areas rely heavily on groundwater. The consequences of climate change on groundwater are long term and can be far reaching. One of the more apparent consequences is the increased migration of salt water inland in coastal aquifers. Using two coastal aquifers, one in Egypt and the other in India, this study investigates the effect of likely climate change on sea water intrusion. Three realistic scenarios mimicking climate change are considered. Under these scenarios, the Nile Delta aquifer is found to be more vulnerable to climate change and sea level rise. Copyright © 1999 John Wiley & Sons, Ltd.     

Impact of climate change on the hydrology and water salinity in the Anzali Wetland,northern Iran

ABSTRACT

The impact of climate change on hydrology and water salinity of a valuable coastal wetland (Anzali) in northern Iran is assessed using daily precipitation and temperature data from 19 models of Coupled Model Inter-comparison Project Phase 5. The daily data are transiently downscaled using the Long Ashton Research Station Weather Generator to three climatic stations. The temperature is projected to increase by +1.6, +1.9 and +2.7°C and precipitation to decrease by 10.4%, 12.8% and 12.2% under representative concentration pathway (RCP) scenarios RCP2.6, RCP4.5 and RCP8.5, respectively. The wetland hydrology and water salinity are assessed using the water balance approach and mixing equation, respectively. The upstream river flow modelled by the Soil and Water Assessment Tool is projected to reduce by up to 18%, leading to reductions in wetland volume (154 × 10⁶ m³), area (57.47 km²) and depth (2.77 m) by 34%, 21.1% and 20.2%, respectively, under climate change, while the mean annual total dissolved solids (1675 mg/L) would increase by 49%. The reduced volume and raised salinity may affect the wetland ecology.     

Prediction and prevention of the impacts of sea level rise on the Yangtze River Delta and its adjacent areas

The Yangtze River Delta region is characterized by high density of population and rapidly developing economy. There are low lying coastal plain and deltaic plain in this region. Thus, the study area could be highly vulnerable to accelerated sea level rise caused by global warming. This paper deals with the scenarios of the relative sea level rise in the early half period of the 21st century in the study area. The authors suggested that relative sea level would rise 25 50 cm by the year 2050 in the study area, of which the magnitude of relative sea level rise in the Yangtze River Delta would double the perspective worldwide average. The impacts of sea level rise include: (i) exacerbation of coastline recession in several sections and vertical erosion of tidal flat, and increase in length of eroding coastline; (ii) decrease in area of tidal flat and coastal wetland due to erosion and inundation; (iii) increase in frequency and intensity of storm surge, which would threaten the coastal protection works; (iv) reduction of drainage capacity due to backwater effect in the Lixiahe lowland and the eastern lowland of Taihu Lake region, and exacerbation of flood and waterlogging disasters; and (v) increase in salt water intrusion into the Yangtze Estuary. Comprehensive evaluation of sea level rise impacts shows that the Yangtze River Delta and eastern lowland of Taihu Lake region, especially Shanghai Municipality, belong in the district in the extreme risk category and the next is the northern bank of Hangzhou Bay, the third is the abandoned Yellow River delta, and the district at low risk includes the central part of north Jiangsu coastal plain and Lixiahe lowland.     

Effects of mixed physical barrier on residual saltwater removal and groundwater discharge in coastal aquifers

Physical barriers are widely used to control seawater intrusion (SWI). Amongst different kinds of physical barriers, mixed physical barriers (MPBs) are shown to be an effective approach to prevent SWI. However, the system may hinder the discharge of fresh groundwater and the removal of residual saltwater trapped in the inland aquifers of MPBs. Herein, using the validated numerical model, for the first time, we investigated the dynamics of residual saltwater and groundwater discharge after the installation of MPBs. For examining the applicability of MPB and its response to structural variations and hydraulic gradient, the comparison with traditional physical barriers and sensitivity analysis was also carried out. The MPB increased the mixing area of freshwater and saltwater at the beginning of the removal process, resulting in the reduction of the saltwater wedge length (R_L) by 74.6% and the removal of total salt mass (R_M) by 62.6% within the 4% of the total removal time. Meanwhile, the groundwater discharge (Q') rose rapidly after a sharp decline from 100% to 40% in the first stage. As the residual saltwater wedge was retreated, the mixing intensity and removal efficiency decreased substantially in the second stage. Similarly, Q' raised with a declining rate at this stage. The removal efficiency was positively correlated with wall depth and hydraulic gradient and there were optimal distance of the middle spacing and height of lower dam to reach the highest efficiency. The groundwater discharge reduced monotonously with the increase of dam height and wall depth as well as the decrease of barrier spacing and hydraulic gradient. Under certain conditions, the efficiency of MPB in removing residual saltwater could be 40%–100% and 0%–56% higher than that of traditional subsurface dam and cutoff wall, respectively. The laboratory scale conclusions provide valuable physical insight for the real field applications regarding dynamic mechanism and regularity. These findings will always help decision makers choose proper engineering measures and protect groundwater resources in coastal areas.     

Effects of urbanization on stream hydrology and water quality: the Florida Gulf Coast

At the global scale, the population density of coastal areas is nearly three times that of inland areas, and consequently, land development represents a threat to coastal ecosystems. It is critical to understand how increasing urbanization affects coastal watersheds. To that end, the objective of this study was to examine the influence of urban development on stream water quality and hydrology in a coastal setting, a scenario that has received less attention than other physiographic regions. Stream hydrologic, physicochemical, and microbial data were collected in watersheds near Apalachicola, Florida with a range of impervious surfaces from 0 to 15%. Watersheds with greater impervious cover exhibited higher pH, specific conductance, and temperature, elevated nutrient concentrations and loads (, and total phosphorus), higher bacterial concentrations (fecal coliform and Escherichia coli), and increased maximum flow and hydrograph flashiness. Different responses to development here compared to other physiographic regions included lower total suspended solid concentrations, higher total dissolved solid concentrations, and a lack of response of base flow to increased urbanization. Additionally, Na⁺ and Cl^? concentrations were elevated to a greater extent than is often the case in non‐coastal areas. In the coming years, urban development is projected to increase substantially in coastal zones and thus there is risk of further stream degradation in coastal watersheds. Copyright © 2011 John Wiley & Sons, Ltd.     

三峡水库175 m试验性蓄水期调度运行对洞庭湖蓄水量变化的影响

长江干流与洞庭湖存在复杂的并联型分汇关系,当三峡水库调度改变长江径流过程时,会引起洞庭湖年内槽蓄量的变化,对于洞庭湖地区防洪、水资源配置和水环境保护产生显著的影响.本文建立了枝城至螺山站的荆江-洞庭湖水流模型,利用2008-2017年的三峡水库实际调度日数据,分析有、无三峡水库调度两种情况下洞庭湖槽蓄量的变化过程,同时利用建库前和近期的水位流量关系反映河道过流能力,分析了河道调整的影响.结果表明:由河道调整引起的槽蓄量变化在汛前消落期、汛期、汛末蓄水期和枯水期分别为-3.06%、0.12%、-0.01%和-13.31%.有三峡水库影响情况下,汛前消落期由于荆江"三口"进入洞庭湖的多年平均总径流增加23.94%,洞庭湖出口处城陵矶多年平均水位升高0.53 m,阻碍了洞庭湖出流,洞庭湖多年平均槽蓄量增长13.30%;汛期由于荆江"三口"分流量减少3.54%,城陵矶水位降低0.02 m导致出湖流量增多,因此洞庭湖多年平均槽蓄量减少0.20%;在汛末蓄水期,荆江"三口"分入洞庭湖的多年平均总径流量减少37.18%,城陵矶多年平均水位降低1.33 m,导致出湖流量增多,因而洞庭湖多年平均槽蓄量减少27.74%;在枯水期,荆江"三口"多年平均总径流量增加5.61%,城陵矶多年平均水位上升0.07 m,最终洞庭湖多年平均枯期槽蓄量增加2.96%.     

Management of sustainable ecological water levels of endorheic salt lakes in the Inner Mongolian Plateau of China based on eco-hydrological processes

Hydrologic regime plays an important role in maintaining aquatic ecosystem structures and biogeochemical processes of endorheic salt lakes. Due to joint influences of regional climate change, runoff regulation and water withdrawal, ecological water deficiency has been increasingly prominent in endorheic salt lakes in Northwest China, especially in the Inner Mongolian Plateau. Previous studies mainly focused on establishing and applying methods to determine ecological water levels of lakes, while much less attention was paid to a more important problem – how such water levels could be reached under changed watershed hydrological processes. Solutions of this gap were explored in this study using the Dalinuoer Lake as an example. This lake is a typical endorheic salt lake located in the Inner Mongolian Plateau. It is a critical source to provide important ecological services and economic values for locals. Its ecological water level to maintain the optimum salinity threshold was first calculated by applying a statistical analysis of relationships between the phytoplankton biomass, salinity and water level of the lake. Potential measures to preserve the ecological water level of the lake were subsequently evaluated based on a hydrological process analysis of the watershed. The results indicated that the optimum salinity threshold was 5.7 g/L. This value should be also valid for other endorheic salt lakes in this region. According to a function between the water storage and the mean water depth of this lake, the ecological water level was determined to be 10.28 m with an ecological water deficit of 2.5 × 10⁸ m³. A basin water balance analysis using the results proposed measures to maintain a sustainable ecological water level, including controlling local water consumption and infusing ecological water. The results of this study could be extrapolated to other similar conditions to provide guidance for policy-makers, so that better decisions could be hopefully forged to protect eco-hydrological processes of endorheic salt lakes in the Mongolian Plateau, as well as other comparable scenarios.