Effect of strip recharge on sea water intrusion into aquifers

Abstract

Parametric studies were carried out to analyse the effect on sea water intrusion of freshwater recharge through a finite width strip parallel to the coast. A vertically integrated one-dimensional finite element model was used for this purpose. The studies included the analysis of the effect of location, width, intensity and the period of recharge on sea water-freshwater interface motion. Relationships were established between the interface motion and the recharge parameters applicable to wide ranging practical cases. From the studies, the ideal location for recharge was identified to achieve the maximum repulsion of intrusion. The width of recharge also affects the interface motion and the widths greater than 2% of the initial intrusion length were effective in controlling the intrusion. The results indicated that the reduction of intrusion up to 30% could be achieved through strip recharge.     

Stack unit mapping of coastal aquifer to predict and control sea water intrusion using remote sensing and a geographical information system

Aquifers are inherently susceptible to contamination and coastal aquifers in specific are highly vulnerable to sea water intrusion. For efficient planning and management of coastal aquifers in Kayalpattu and Tiruchopuram villages, which extend over 4·05 km², it is essential to delineate and predict the extent of intrusion into the shallow aquifer. Management of ground water in coastal aquifers is composed of major elements that should be properly evaluated, and special attention is given to the sea water intrusion problem. Different data, like hydro‐geomorphological and depth‐wise iso‐apparent resistivity, are integrated spatially using a geographical information system. The stack‐unit mapping approach is used to delineate the zones with iso‐apparent resistivity of less than 10 Ω m have been found to be increasing in areal extent with reference to depth. Copyright © 2003 John Wiley & Sons, Ltd.     

The impact of highly permeable layer on hydraulic system in a coastal aquifer

This study is aimed to understand the hydraulic mechanism of coastal aquifer systems that include highly permeable layers (HPLs). These hydrologic conditions can be found in many volcanic islands that are composed of a series of lava flows discharged into sea or other standing body of water. In the first part, we developed a numerical model based on the geologic and hydrologic data obtained from the eastern Jeju Island, Korea, of which the aquifer contains clinker and hyaloclastite layers. The simulation results reproduced spatial location of fresh‐saline water interface, especially the abrupt decline of interface at the inland part and the thickness variation of transition zone along the cross‐section observed at the eastern Jeju coastal aquifer. We were able to find out that these phenomena are strongly related to the presence of the HPL. In the second part, quantitative analyses were conducted with the use of hypothetical models in order to understand the dynamic characteristics of coastal system that includes HPLs. A series of sensitivity studies were conducted to assess the effect of the horizontal length and vertical depth of HPL on the spatial location of the interface toe and the configuration of transition zone. Various case studies have shown that the seawater intruded into the inland more as the horizontal length of HPL was increased and its vertical depth was decreased. In other simulations including two HPLs, the vertical distance between these two HPLs primarily controlled the flow regime, flux variations, and the configuration of the transition zone. Finally, we performed simulations to evaluate the effect of a rising sea‐level. This study provides more understanding of how the presence of HPL controls the seawater intrusion processes, and the spatial configurations of fresh‐saline water interface at coastal aquifers. Copyright © 2012 John Wiley & Sons, Ltd.     

Discussion about the validity of sharp‐interface models to deal with seawater intrusion in coastal aquifers

Analytical models have been exhaustively used to study simple seawater intrusion problems and the sustainable management of groundwater resources in coastal aquifers because of its simplicity, easy implementation, and low computational cost. Most of these models are based on the sharp‐interface approximation and the Ghyben–Herzberg relation, and their governing equations are expressed in terms of a single potential theory to calculate critical pumping rates in a coastal pumping scenario. The Ghyben–Herzberg approach neglects mixing of fresh water and seawater and implicitly assumes that salt water remains static. Therefore, the results of the analytical solutions may be inaccurate and unacceptable for some real‐complex case studies. This paper provides insight into the validity of sharp‐interface models to deal with seawater intrusion in coastal aquifers, i.e. when they can be applied to obtain accurate enough results. For that purpose, this work compares sharp‐interface solutions, based on the Ghyben–Herzberg approach, with numerical three‐dimensional variable‐density flow simulations for a set of heterogeneous groundwater flow and mass transport parameters, and different scenarios of spatially distributed recharge values and spatial wells placement. The numerical experiment has been carried out in a 3D unconfined synthetic aquifer using the finite difference numerical code SEAWAT for solving the coupled partial differential equations of flow and density‐dependent transport. This paper finds under which situations the sharp‐interface solution gives good predictions in terms of seawater penetration, transition zone width and critical pumping rates. Additionally, the simulation runs indicate to which parameters and scenarios the results are more sensitive. Copyright © 2013 John Wiley & Sons, Ltd.     

The impact of climate change on sea level rise at Peninsular Malaysia and Sabah–Sarawak

The sea level change along the Peninsular Malaysia and Sabah–Sarawak coastlines for the 21st century is investigated along the coastal areas of Peninsular Malaysia and Sabah–Sarawak because of the expected climate change during the 21st century. The spatial variation of the sea level change is estimated by assimilating the global mean sea level projections from the Atmosphere–Ocean coupled Global Climate Model/General Circulation Model (AOGCM) simulations to the satellite altimeter observations along the subject coastlines. Using the assimilated AOGCM projections, the sea level around the Peninsular Malaysia coastline is projected to rise with a mean in the range of 0.066 to 0.141 m in 2040 and 0.253 m to 0.517 m in 2100. Using the assimilated AOGCM projections, the sea level around Sabah–Sarawak coastlines is projected to rise with a mean in the range of 0.115 m to 0.291 m in 2040 and 0.432 m to 1.064 m in 2100. The highest sea level rise occurs at the northeast and northwest regions in Peninsular Malaysia and at north and east sectors of Sabah in Sabah–Sarawak coastline. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of a coarse interlayer on seawater intrusion and contaminant migration in coastal aquifers

Vertical 2D slice laboratory experiments were carried out in homogenous and layered sand tanks to elucidate the effects of a highly permeable (coarse‐grained sand) interlayer on seawater intrusion and transport of contaminants to a coastal sea. Tidal fluctuations produced oscillations in the seawater–freshwater transition zone, fluctuations of the contaminant infiltration rate and a zigzag contaminant plume outline. The seawater wedge became discontinuous at the (vertical) edges of the interlayer because of increased lateral movement of the seawater–freshwater interface within the interlayer. The contaminant plume formed a tail within the interlayer depending on the tidal stage, and similar to the wedge, its movement was accentuated. A simple analytical model that neglected vertical flow reliably predicted steady‐state seawater intrusion into the coastal aquifer. Numerical modeling was used to gain insight into the groundwater hydrodynamics and contaminant migration. The numerical results confirmed the experimental findings, i.e. that a highly permeable interlayer can provide a rapid transit path for contaminants to reach the seaward boundary and that the interlayer amplifies the effects of tidal fluctuations, resulting in wider transition zones for the seawater wedge and contaminant plume. Numerical simulations further showed that, with increasing interlayer hydraulic conductivity, the maximum seawater intrusion distance inside the interlayer increases approximately linearly. For the fixed‐head contaminant injection condition used, the model showed that contaminant infiltration increases approximately logarithmically with increasing interlayer hydraulic conductivity (other factors held fixed). Copyright © 2013 John Wiley & Sons, Ltd.     

Impacts of climate change on water resources in Spain

Abstract

Impacts on water resources produced by climate change can be exacerbated when occurring in regions already presenting low water resources levels and frequent droughts, and subject to imbalances between water demands and available resources. Within Europe, according to existing climate change scenarios, water resources will be severely affected in Spain. However, the detection of those effects is not simple, because the natural variability of the water cycle and the effects of water abstractions on flow discharges complicate the establishment of clear trends. Therefore, there is a need to improve the assessment of climate change impacts by using hydrological simulation models. This paper reviews water resources and their variability in Spain, the recent modelling studies on hydrological effects of climate change, expected impacts on water resources, the implications in river basins and the current policy actions.

Editor Z.W. Kundzewicz

Citation Estrela, T., Pérez-Martin, M.A., and Vargas, E., 2012. Impacts of climate change on water resources in Spain. Hydrological Sciences Journal, 57 (6), 1154–1167.     

Modeling of climate change impacts on Lake Burullus,coastal lagoon (Egypt)

Coastal lagoons are particularly vulnerable to climate change, in particular, Sea Level Rise (SLR) due to their shallowness. Lake Burullus provides a variety of socio-economic services as the second largest coastal lagoon in Egypt. Recently, it has experienced significant ecological deterioration. Thus, its ecosystem is fragile in the face of anthropogenic induced changes. The main objective of the current study is to investigate the climate change impacts on characteristics of Lake Burullus. A depth averaged hydro-ecological modeling system, MIKE21, was applied to develop an eco - hydrodynamic model for the lake. The developed model was calibrated and verified for two successive years: July 2011–June 2012 and July 2012–June 2013. The model simulations exhibited good agreement with the measurements during the calibration and verification processes. Six different Regional Climate Models (RCMs) were compared, using six different statistical metrics, to determine the most accurate one for the study area. The required meteorological input, including surface air temperature, precipitation, and evaporation were derived from the selected RCM. The meteorological input was extracted for two different years in the 21 ^st century considering one Representative Concentration Pathways (RCPs) scenario, based on the Intergovernmental Panel on Climate Change (IPCC) 5th Report. Regional SLR projections for the Mediterranean Sea for the selected RCP scenario and the two studied years were obtained. These future climate change estimates were used to modify the validated model of the lake. A sensitivity analysis was applied to assess effect of future climatic conditions and SLR, separately. The results revealed that the lake water depths will increase and it will be warmer and more saline. Significant spatial variability of the studied parameters under climate change forcing is expected. Consequently, climate change is going to restrict the lake's ability to preserve the present-day species. An urgent management plan involving adaptation works, should be implemented to reduce such potential species losses in Egyptian lagoons.     

Transience of seawater intrusion and retreat in response to incremental water‐level variations

This paper provides for the first time an experimental study where the impact of sea‐level fluctuations and inland boundary head‐level variations on freshwater–saltwater interface toe motion and transition zone dynamics was quantitatively analysed under transient conditions. The experiments were conducted in a laboratory flow tank where various (inland and coastal) head changes were imposed to the system and the response of the key seawater intrusion parameters was analysed with high spatial and temporal resolution. Two homogeneous aquifer systems of different grain size were tested. The numerical code SEAWAT was used for the validation. The results show that in cases of sea‐level variations, the intruding wedge required up to twice longer time to reach a new steady‐state condition than the receding wedge, which thereby extend the theory of timescale asymmetry between saltwater intrusion and retreat processes in scenarios involving sea‐level fluctuations. The intruding and receding rates of the saltwater wedge were respectively similar in the scenario involving sea‐level and the freshwater‐level changes, despite change in transmissivity. The results show that, during the intrusion phase, the transition zone remains relatively insensitive, regardless of where the boundary head change occurs (i.e., freshwater drop or sea‐level rise) or its magnitude. By contrast, a substantial widening of the transition zone was observed during the receding phase, with almost similar amplitude in the scenario involving a rise of the freshwater level compared with that caused by a drop of the saltwater level, provided that an equivalent absolute head change magnitude was used. This transition zone widening (occurring during saltwater retreat) was greater and extended over longer period in the low hydraulic conductivity aquifer, for both freshwater‐level rise and sea‐level drop scenarios. The concentration maps revealed that the widening mechanism was also enhanced by the presence of some freshwater sliding and into the wedge during saltwater retreat, which was thereafter sucked upward towards the interface because of density difference effects.     

Imprints of wave climate and mean sea level variations in the dynamics of a coastal spit over the last 250 years: Cap Ferret,SW France

In coastal areas, sea level rise (SLR) and changing wave climates are expected to be the main oceanic drivers of shoreline adjustments. These drivers have been shown to vary on a wide spectrum of spatial and temporal scales. Nonetheless, a general rule about how this variability impacts global shorelines remains to be articulated. Here, we discuss the impacts of wave climate changes and SLR on the evolution of a barrier spit–inlet system over the last 250 years. The distal end of the Cap Ferret barrier spit, SW France, has undergone large-scale oscillations that were well correlated with variations of the decadal average of the winter North Atlantic Oscillation (NAO) index. The local wave climate hindcast supports that increased alongshore wave energy fluxes associated with the positive phase of the NAO were responsible for the updrift retreat of the spit. By opposition, the spit has elongated downdrift when waves were less energetic and more shore normal, as during the negative phase of the NAO. In addition, lower rates of SLR appeared to be necessary for the spit to develop, as higher rates of SLR very likely forced the adjacent inlet to enlarge, at the expense of the spit. These results should help to predict and detect coastal adjustments driven by climate change and by climate variability. © 2019 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.     

Cost-efficient management of coastal aquifers via recharge with treated wastewater and desalination of brackish groundwater: application to the Akrotiri basin and aquifer,Cyprus

Abstract

We investigate the general methodology for an intensive development of coastal aquifers, described in a companion paper, through its application to the management of the Akrotiri aquifer, Cyprus. The Zakaki area of that aquifer, adjacent to Lemessos City, is managed such that it permits a fixed annual agricultural water demand to be met, as well as and a fraction of the water demand of Lemessos, which varies according to available surface water. Effluents of the Lemessos wastewater treatment plant are injected into the aquifer to counteract the seawater intrusion resulting from the increased pumping. The locations of pumping and injection wells are optimized based on least-cost, subject to meeting the demand. This strategy controls sea intrusion so effectively that desalting of only small volumes of slightly brackish groundwater is required over short times, while ～2.3 m³ of groundwater is produced for each 1 m³ of injected treated wastewater. The cost over the 20-year period 2000–2020 of operation is ～40 M€ and the unit production cost of potable water is under 0.2 €/m³. The comparison between the deterministic and stochastic analyses of the groundwater dynamics indicates the former as conservative, i.e. yielding higher groundwater salinity at the well. The Akrotiri case study shows that the proposed aquifer management scheme yields solutions that are preferable to the widely promoted seawater desalination, also considering the revenues from using the treated wastewater for irrigation.

Citation Koussis, A. D., Georgopoulou, E., Kotronarou, A., Mazi, K., Restrepo, P., Destouni, G., Prieto, C., Rodriguez, J. J., Rodriguez-Mirasol, J., Cordero, T., Ioannou, C., Georgiou, A., Schwartz, J. & Zacharias, I. (2010) Cost-efficient management of coastal aquifers via recharge with treated wastewater and desalination of brackish groundwater: application to the Akrotiri basin and aquifer, Cyprus. Hydrol. Sci. J. 55(7), 1234–1245.     

Cost-efficient management of coastal aquifers via recharge with treated wastewater and desalination of brackish groundwater: general framework

Abstract

Semi-arid coastal zones often suffer water-stress, as water demand is high and markedly seasonal, due to agriculture and tourism. Driven by scarcity of surface water, the communities in semi-arid coastal regions turn to aquifers as prime water source; but intensive exploitation of coastal aquifers causes seawater intrusion, which degrades the quality of groundwater. The cost-efficient and sustainable development of coastal aquifers can be achieved through a holistic management scheme which combines two non-traditional water sources: (a) saltwater, to be treated to the desired quality, and (b) wastewater, to be re-claimed to augment aquifer recharge for control of seawater intrusion, and also to meet certain demands. This management scheme is based on the idea that it is cost-advantageous to: (i) desalt brackish groundwater, instead of seawater, as the former requires far less energy, and (ii) to re‐use wastewater at only the differential cost to any treatment already practiced. In this paper, we present the general framework of the proposed management scheme, and a decision aid tool (DAT) which has been developed to assist decision makers to explore the scheme's decision space. The DAT uses cost as optimization criterion to screen various management scenarios, via modelling of the dynamic natural-engineered system behaviour, and identifies those cost-efficient ones that meet the water demand and achieve aquifer protection.

Citation Koussis, A. D., Georgopoulou, E., Kotronarou, A., Lalas, D. P., Restrepo, P., Destouni, G., Prieto, C., Rodriguez, J. J., Rodriguez-Mirasol, J., Cordero, T. & Gomez-Gotor, A. (2010 Koussis, A. D., Georgopoulou, E., Kotronarou, A., Mazi, K., Restrepo, P., Destouni, G., Prieto, C., Rodriguez, J. J., Rodriguez-Mirasol, J., Cordero, T., Schwartz, J., Ioannou, C., Georgiou, A. and Zacharias, I. 2010. Cost-efficient management of coastal aquifers in water-stressed regions via recharge with treated wastewater and desalination of brackish groundwater: application to the Akrotiri basin and aquifer, Cyprus. Hydrol. Sci. J, 55(7): 1234–1245. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) Cost-efficient management of coastal aquifers via recharge with treated wastewater and desalination of brackish groundwater: general framework. Hydrol. Sci. J. 55(7),1217–1233.     

Prediction of groundwater‐induced flooding in a chalk aquifer for future climate change scenarios

Current climate change models for the southeast UK predict changing rainfall patterns, with increased incidence of extreme events. The chalk aquifer in the UK and northern France is susceptible to groundwater‐induced flooding under such conditions. In this methodological study we apply a frequency domain analysis approach to the chalk aquifer to derive a transfer function between effective rainfall and groundwater level from 7 years of monitoring data from the North Heath Barn site, near Brighton. The derived transfer function was calibrated and validated against monitoring data and then used to predict groundwater level for rainfall models for high, medium and low emission scenarios from the UKCP09 database. The derived transfer function is most closely comparable to the linear aquifer model, despite evidence for both matrix and fracture or karst water flow in the chalk, with transmissivity and unconfined storativity at the catchment scale of 1548 m² day^?1 and 1.6 × 10^?2. The application of the transfer function to UKCP09 rainfall data suggests that groundwater‐induced flooding may be about four times more frequent by 2040–2069 compared with 1961–1990 and seven times more frequent by 2070–2099. The model data also suggest an increase in the duration of groundwater minima relative to the reference period. Compared to deterministic modelling which requires detailed knowledge of aquifer heterogeneity and processes, the transfer function approach, although with limitations, is simpler, incorporating these factors into the analysis through frequency and phase coefficients, and thus may have the potential for groundwater risk assessment in other areas. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Saltwater intrusion modelling in Jorf coastal aquifer,South‐eastern Tunisia: geochemical,geoelectrical and geostatistical application

Marine intrusion is the most serious problem facing the coastal Jorf shallow aquifer, located in south‐eastern Tunisia on the Mediterranean Sea. Jorf Aquifer is intensively exploited to supply the growing needs of agriculture and domestic sectors. This work proposes a multidisciplinary investigation, involving hydro‐geochemical, geoelectrical survey and geostatistical techniques for modelling the saltwater intrusion. For this purpose, 36 water samples were conducted and analysed. Electric conductivity, pH, total dissolved solids and major ions were measured and analysed. Pie and Durov Diagrams, Q‐mode hierarchical cluster and geostatistical analysis were considered to identify the main groundwater mineralization processes. Results revealed that the Na‐Cl‐Ca‐SO₄ is the dominant water type suggesting that dissolution of halite and gypsum was the main mineralization source of groundwater in the central and southern part of study area. However, saltwater intrusion was shown to control groundwater quality essentially in coastal areas. Variographic analyses were used to select the variographic model that best fits the spatial development of apparent resistivity. Kriged apparent resistivity profiles showed an abnormal decrease of resistivity values in the coastal zone, implying highly saline water because of seawater intrusion. Apparent resistivity values also decrease considerably in the faulted areas, suggesting a contribution of faults to seawater intrusion. Finally, saltwater mixing ratio was computed for each sample, and a refined seawater intrusion map was developed. Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

Apparent dynamic stability of the southeast African coast despite sea level rise

The coast of southeast Africa is dominated by sandy beaches that tend to be confined within log‐spiral or headland‐bound embayments. Investigations using serendipitous air imagery data set have been previously undertaken and conclusions drawn about the stability of the coast. We show that conclusions drawn from this data, with respect to the high water mark (HWM) position are fraught with errors, which include tidal state, pressure regime, beach slope, high‐swell erosion, seasonal and multi‐annual changes. We highlight and discuss these sources of error, together with their magnitudes. The most significant of these are the high‐swell, seasonal and multi‐annual variations. From case studies we show that the seasonal beach rotation and long‐term beach width variation are responsible for tens of metres of unaccounted HWM variation, 30 to 50 m is common, with maximums reaching 60 to 100 m. Overall the southeast African coastline appears to be in a state of long‐term dynamic equilibrium. There is no evidence of any sea‐level rise‐forced transgression in the coastal sediment budget, despite sea‐level rise (SLR). If such a signal is, in fact present, it is lost within the beach width variation. Some southeast African coastal reaches are suffering chronic erosion, but these are related to anthropogenic impacts. The extreme difficulty of placing a HWM, with any temporal validity on this coast precludes the routine use of the Bruun Rule. Although no transgressive signature is found, there is evidence of a decreasing coastal sand budget as a result of anthropogenic or natural climate change, or both. This decrease in the coastal sand volume is likely to result in increased future erosion. Copyright © 2016 John Wiley & Sons, Ltd.     

华南沿海地区验潮站资料反映的海平面变化与海岸升降

根据收集到的２５个验潮站资料,表明近几十年来华南沿海海平面大约平均以１．４５ｍｍ／ａ的速率上升,与全球海平面升高速率１．５ｍｍ／ａ接近。由各验潮站海平面的升降速率与全球海平面平均升高速率比较,得到验潮站所在海岸地壳速率在４．４～－４．１ｍｍ／ａ之间。其运动方向与由滨海相样品反映的晚更新世及全新世以来的海岸升降趋势大体相同,即现今海岸主要为中、晚全新世以来的继承性运动。