Impact of estuarine reclamation projects on saltwater intrusion and freshwater resource

Estuarine projects can change local topography and influence water transport and saltwater intrusion.The Changjiang(Yangtze)River estuary is a multichannel estuary,and four major reclamation projects have been implemented in the Changjiang River estuary in recent years:the Xincun Shoal reclamation project(RP-XCS),the Qingcao Shoal reclamation project(RP-QCS),the Eastern Hengsha Shoal reclamation project(RP-EHS),and the Nanhui Shoal reclamation project(RP-NHS).The effects of the four reclamation projects and each project on the saltwater intrusion and water resources in the Changjiang River estuary were simulated in a 3D numerical model.Results show that for a multichannel estuary,local reclamation projects change the local topography and water diversion ratio(WDR)between channels and influence water and salt transport and freshwater utilization in the estuary.During spring tide,under the cumulative effect of the four reclamation projects,the salinity decreases by approximately 0.5in the upper reaches of the North Branch and increases by 0.5-1.0 in the middle and lower reaches of the North Branch.In the North Channel,the salinity decreases by approximately 0.5.In the North Passage,the salinity increases by 0.5-1.0.In the South Passage,the salinity increases by approximately 0.5 in the upper reaches and decreases by 0.2-0.5 on the north side of the middle and lower reaches.During neap tide,the cumulative effects of the four reclamation projects and the individual projects are similar to those during spring tide,but there are some differences.The effects of an individual reclamation project on WDR and saltwater intrusion during spring and neap tides are simulated and analyzed in detail.The cumulative effect of the four reclamation projects favors freshwater usage in the Changjiang River estuary.

Investigation of saltwater intrusion and salinity stratification in winter of 2007/2008 in the Zhujiang River Estuary in China

Saltwater intrusion is a serious environmental problem in the Zhujiang River Estuary (ZRE),which threatens the water supply of fifteen million people. The hydrological observations as well as meteorological and tidal forcing in the winter of 2007/2008 were analyzed to examine the saltwater intrusion in the ZRE.The observational results suggest that the maximum vertical difference of salinity can reach 10 in the Humen Channel during neap tide,but is very small in the Hengmen Channel. The vertically averaged salinity from time series stations during spring tide is higher than that during neap tide.A three-dimensional finite difference model was developed based on the environmental fluid dynamic code (EFDC) to study the mechanism of saltwater intrusion and salinity stratification in the ZRE.By analyzing the salt transport and the temporal variation of saltwater intrusion,the authors found that the net salt transport due to the estuarine circulation during neap tide was more than that during spring tide.This caused salt to advance more into the estuary during neap tide.However,saltwater intrusion was stronger during spring tide than that during neap tide because the spring-neap variation in salt transport was small relative to the total length of the saltwater intrusion.The physical mechanism causing this saltwater intrusion was investigated by a series of sensitivity experiments,in order to examine saltwater intrusion in response to river discharge and winds.The freshwater source was a dominant influencing factor to the saltwater intrusion and controlled salinity structure,vertical stratification and length of the saltwater intrusion.The prevailing northeast monsoon during winter could increase the saltwater intrusion in the ZRE.Though the southwest wind was uufavorable to saltwater intrusion during spring tide,it could increase stratification and saltwater intrusion during neap tide.

Impact of the eastern water diversion from the south to the north project on the saltwater intrusion in the Changjiang Estuary in China

The south to the north project (WDP) on the saltwater intrusion in the Changjiang Estuary is studied by the improved three-dimensionai (3D) numerical model.The net unit width flux in the Changjiang Estuary as well as the sectional salt flux is calculated in the North Branch (NB),the South Branch (SB),the North Channel (NC),the South Channel (SC),the North Passage (NP) and the South Passage (SP),respectively.The net seaward water flux in the SB is reduced,and the net water flux spilling over from the NB to the SB is enhanced after the eastern WDP.Under the mean river discharge condition in the dry season,the net salt flux spilling over from the NB to the SB is increased by 2.09 t/s and 0.52 t/s during the spring and neap tides,respectively,due to the eastern WDP.The saltwater intrusion in the Changjiang Estuary is enhanced by the eastern WDP.Compared with that during the spring tide,the net water diversion ratio during the neap tide in the NC is smaller,and thus the enhancement of the saltwater intrusion by the eastern WDP is smaller in the NC,and larger in the NP and the SP.The tidally averaged surface salinity at the water intakes of the Dongfengxisha Reservoir,the Chenhang Reservoir and the Qingcaosha Reservoir rises both during the spring and neap tides.

Impact of seasonal tide variation on saltwater intrusion in the Changjiang River estuary

An improved 3-D ECOM-si model was used to study the impact of seasonal tide variation on saltwater intrusion into the Changjiang River estuary, especially at the bifurcation of the North Branch （NB） and the South Branch （SB）. The study assumes that the fiver discharge and wind are constant. The model successfully reproduced the saltwater intrusion. During spring tide, there is water and salt spillover （WSO and SSO） from the NB into the SB, and tidally averaged （net） water and salt fluxes are 985 m3/s and 24.8 ton/s, respectively. During neap tide, the WSO disappears and its net water flux is 122 m3/s. Meanwhile, the SSO continues, with net salt flux of 1.01 ton/s, much smaller than during spring tide. Because the tidal range during spring tide is smaller in June than in March, overall saltwater intrusion is weaker in June than in March during that tidal period. However, the WSO and SSO still exist in June. Net water and salt fluxes in that month are 622 m3/s and 15.35 ton/s, respectively, decreasing by 363 m3/s and 9.45 ton/s over those in March. Because tidal range during neap tide is greater in June than in March, saltwater intrusion in June is stronger than in March during that tidal period. The WSO and SSO appear in June, with net water and salt fluxes of 280 m3/s and 8.55 ton/s, respectively, increasing by 402 m3/s and 7.54 ton/s over those in March. Saltwater intrusion in the estuary is controlled by the fiver discharge, semi-diurnal flood-ebb tide, semi-monthly spring or neap tide, and seasonal tide variation.

Impacts of Different Dynamic Factors on the Saltwater Intrusion in the Northern Branch of the Yangtze Estuary

A 3-D baroclinic numerical model is established to study the temporal and spatial distribution of salinity in the Northern Branch(NB) of the Yangtze Estuary(YE) in response to river runoff, wind and currents. The idealized,process-oriented studies show that the lower river runoff in the dry season is the main driving factor for the spilling over from the NB to the Southern Branch(SB). The NB takes longer time to get in dynamic stable state compared with the SB, as the runoff transfers from the wet season to the dry season. The vertical stratification intensity of the NB has obvious periodic phenomena in the dry season, and the stratification strength is enhanced under the action of low runoff and north wind, which further weakens the vertical transport of water. Momentum balance analysis suggested that the landward net flux increases when considering the influence of the moderate north wind, and the landward flux will enhance if considering the boundary current during the spring tide. With the influence of the boundary current, increases the average salinity of the NB, as well as the intrusion degree from the NB to the SB.This indicates that the nearshore ocean current of the Yellow Sea is an important factor affecting the saltwater intrusion in the NB of the YE.

Features and evaluation of sea/saltwater intrusion in southern Laizhou Bay

Understanding the degree of sea/saltwater intrusion in coastal regions is of great significance to treating the intrusion and improving the environment. Based on the character analysis of the sea/saltwater intrusion, five factors were selected in the fuzzy-synthetical evaluation approach to form the index system, so as to evaluate the degree of sea/saltwater intrusion in southern Laizhou Bay. The results show that the sea/saltwater intrusion is stronger in the middle and northern areas and weaker on the sides and in southern area; currently, the intrusion is relatively serious, and the intrusion area has covered about 68.2% of the areas under study, among which the heavily intruded area is over 50%. Based on the factors analysis of the occurrence and development of sea/saltwater intrusion, the thesis proposes treatment measures.

A Modeling Study on Saltwater Intrusion to Western Four Watercourses in the Pearl River Estuary

Saltwater intrusion has been serious in the Pearl River estuary in recent years. For better understanding and analysis of the saltwater movement to the estuary, the three-dimensional Finite-Volume Coastal Ocean Model （FVCOM） is made to simulate the salinity intrusion to the four western watercourses in the Pearl River estuary under three semilunar conditions. With the measured and simulated Root Mean Square Error （RMSE） and the mean absolute percentage error of water level and salinity at multiple sites, the results show that the numerical water levels, salinity and flow velocities are in agreement with the measured data. It is acceptable and feasible to apply the FVCOM to simulate the salt water intrusion in the western four watercourses of the Pearl River. With the numerical data, the time and spatial movement patterns of saltwater intrusion along the Modao watercourse are analyzed. The salinity contour reaches its peak generally during 3~5 days before the spring tide. The salinity stratification is more obvious in the period of ebb tide than that in the rising tide whether in the spring or neap tides. Salt fluxes reflect changes of salt into the estuary, and the change rules are close to the rules of salinity intrusion.

Modeling of the Groundwater Flow and Saltwater Intrusion in the Coastal Aquifer of Fum Al Wad, Province of Laayoun, Morocco

Saltwater intrusion caused by groundwater over-exploitation from coastal aquifers poses a severe problem in many regions. The Fum Al Wad aquifer is located between Atlantic Ocean in the West and Laayoun in the East. This aquifer covers an area of 250 Km2, and represents an essential water resource for Laayoun city and the periphery regions. It is heavily exploited for water supply, agriculture and industry. The freshwater-saltwater interface is affected by groundwater extraction by public supplies, irrigation wells, and domestic wells in the coastal of this aquifer. The position of the interface is controlled by several factors: these include precipitation, recharge rate, dryness, evapotranspiration, hydraulic conductivity and hydraulic head. Landward migration of the interface freshwater-saltwater often results in a significant decrease in the water resources available for coastal communities. The volume pumped by public for irrigation and the domestic usage in 2010-2011 is estimated 2.5 Mm3/year, and in 2015 about 2.91 Mm3/year only for domestic usages. The objectives of this work are to model the groundwater flow and saltwater intrusion in the coastal aquifer of Fum Al Wad, by SEAWAT-2000 program which coupled both the version of MODFLOW-2000 and MT3DMS. They are designed to simulate variable-density groundwater flow and solute transport in three dimensions. The model is calibrated for hydraulic conductivity, specific yield, porosity, and recharge rate as well as dispersivity coefficient. The result of simulation of the hydrodynamic model during the period of 1986-2015 has revealed a piezometric drawdown with 2.3 m approximately at the level of the pumping zone. Furthermore, this piezometric depression is caused by excessive pumping of the various uses of water and its corresponding that has resulted in the migration of the saltwater intrusion into freshwater with 4.3 km approximately. The simulations result for scenarios 2020 and 2030 of Fum Al Wad aquifer showed a vertical decrease of the piezometric head (about 2.5 m) in 2030, but the saltwater intrusion has advanced diagonally to reach 4.7 km under the freshwater of groundwater of this aquifer.

A saturated saltwater drilling fluid based on salt-responsive polyampholytes

Based on special antipolyelectrolyte effect of zwitterion polymer with same quantity of anionic and cationic charges, we developed two types of salt-responsive polyampholytes, one with high molecular weight and low charge density(HvL) and the other with low molecular weight and high charge density(LvH), by inverse emulsion polymerization. Molecular structure and salt-responsiveness of them were characterized by 1 H-NMR and rheology measurement, respectively. HvL and LvH were evaluated in saturated-salt bentonite suspension and influences of their ratio on apparent viscosity and fluid loss were investigated as well. The results indicate that HvL is better at decreasing fluid loss while LvH is better at maintaining low viscosity. A saturated saltwater drilling fluid centering on HvL and Lv H with simple formula was designed and applied. It is indicated that salt-responsive polyampholytes are fundamentally better than AM-AMPS anionic copolymer and AM-AMPS-DMDAAC amphoteric copolymer. The saturated saltwater drilling fluid has excellent thermal stability, tolerance to bentonite and shale cuttings, and certain resistance to CaCl_2. Salt-responsive polyampholytes can be used in KCl-saturated drilling fluid, with universal adaptability.

3D geomechanical modeling of the response of the Wilzetta Fault to saltwater disposal

From 2009 to 2017,parts of Central America experienced marked increase in the number of small to moderate-sized earthquakes.For example,three significant earthquakes(~Mw 5)occurred near Prague,Oklahoma,in the U.S.in 2011.On 6 Nov 2011,an Mw 5.7 earthquake occurred in Prague,central Oklahoma with a sequence of aftershocks.The seismic activity has been attributed to slip on the Wilzetta fault system.This study provides a 3 D fully coupled poroelastic analysis(using FLAC3 D)of the Wilzetta fault system and its response to saltwater injection in the underpressured subsurface layers,especially the Arbuckle group and the basement,to evaluate the conditions that might have led to the increased seismicity.Given the data-limited nature of the problem,we have considered multiple plausible scenarios,and use the available data to evaluate the hydromechanical response of the faults of interest in the study area.Numerical simulations show that the injection of large volumes of fluid into the Arbuckle group tends to bring the part of the Wilzetta faults in Arbuckle group and basement into near-critical conditions.

Stimulus-responsive mechanism of salt-responsive polymer and its application in saturated saltwater drilling fluid

AM-AMPS-TAC polymers with different charge distribution are synthesized using acrylamide(AM),2-acrylamido-2-methylpropanesulfonate(AMPS)and 3-acrylamidopropyl trimethylammonium(TAC)at different feed ratios by polymerization in solution.The salt-responsive behavior,reasons leading to salt-responsiveness,and effects of polymers molecular structure on salt-responsiveness are studied by laboratory experiments to find out the adaptability of the polymers.Rheology test under stepwise shear mode shows that the AM-AMPS-TAC polymers have salt responsiveness,and the closer the feeds of AMPS and ATC,the more significant the salt responsiveness will be.Conformation change of polymers molecular chain under salt stimulus is studied by turbidity test and micro-morphology analysis,and the responsive mechanism is further investigated by intrinsic viscosity test and copolymer composition analysis.Results indicate that the salt-responsive behavior of AM-AMPS-TAC polymers derives from the"curled to expanded"transition of chain conformation under salt stimulus,and this transition is led by the screening effect of salt which weakens polymers intramolecular ionic bond.Application in saturated saltwater drilling fluid shows that the AM90-AMPS5-TAC5 polymer has the best salt-tolerance and temperature-tolerance when used together with fluid loss controller PAC-Lv.The drilling fluid saturated with NaCl can maintain stable viscosity,good dispersion and low fluid loss for long time under 150℃.

Effect of saltwater intrusion on groundwater environment in Weihe River downstream, Shandong Province, China

Based on the geological and hydrogeological conditions along with dynamic changes of groundwater level,this paper analyzes the hydrodynamic characteristics of saltwater intrusion in the study area.According to monitoring data of groundwater quality,the distribution characteristics of macro component are analyzed,and then fuzzy comprehensive evaluation method is adopted to evaluate the impact of saltwater intrusion on groundwater environment.Concerning the influence degree of groundwater environment,the study area is divided into brine area,seriously influenced area,moderately influenced zone,slightly influenced zone and uninfluenced zone.The results can offer references for prevention and control of saltwater intrusion as well as the protection of water resources.

Groundwater Quality Assessment Based on WQI and Its Vulnerability to Saltwater Intrusion in a Coastal City, Iran

The purpose of this paper was to assess the quality of groundwater in Behshahr (Iran) based on water quality index (WQI). Sixteen water samples from this coastal aquifer were collected and analyzed to study physico-chemical parameters such as pH, hardness, chloride (Cl), electrical conductivity (EC) and total dissolved solids (TDS). The results showed that the annual average of TDS value increased by 343 mg/l between 1999 and 2015 due to anthropogenic activities. According to WQI, it was concluded that the groundwater quality degraded over the last sixteen-year period so that the percentage of samples identified as “good water” decreased by 18.5% and on the other hand, alas, the percentage of “poor water” quality soared by nearly 12.5%. Correspondence of WQI distribution diagram with that of chloride-bicarbonate ratio attests to the significant contribution of saltwater intrusion to groundwater quality deterioration in this area.

Numerical simulation on the process of saltwater intrusion and its impact on the suspended sediment concentration in the Changjiang(Yangtze)estuary

To study the relationship between sediment transportation and saltwater intrusion in the Changjiang (Yangtze) estuary, a three-dimensional numerical model for temperature, salinity, velocity field, and suspended sediment concentration was established based on the ECOMSED model. Using this model, sediment transportation in the flood season of 2005 was simulated for the Changjiang estuary. A comparison between simulated results and observation data for the tidal level, flow velocity and direction, salinity and suspended sediment concentration indicated that they were consistent in overall. Based on model verification, the simulation of saltwater intrusion and its effect on sediment in the Changjiang estuary was analyzed in detail. The saltwater intrusion in the estuary including the formation, evolution, and disappearance of saltwater wedge and the induced vertical circulation were reproduced, and the crucial impact of the wedge on cohesive and non-cohesive suspended sediment distribution and transportation were successfully simulated. The result shows that near the salinity front, the simulated concentrations of both cohesive and non-cohesive suspended sediment at the surface layer had a strong relationship with the simulated velocity, especially when considering a 1-hour lag. However, in the bottom layer, there was no obvious correlation between them, because the saltwater wedge and its inducing vertical circulation may have resuspended loose sediment on the bed, thus forming a high-concentration area near the bottom even if the velocity near the bottom was very low during the transition phase from flood to ebb.

变化条件下长江口防洪御潮及供水保障研究进展与展望

近一个世纪以来,全球气候变暖导致海平面持续上升,增加了整个长江口的水深,抬高了潮汐和风暴潮的基础水位,使得河口咸潮入侵,洪水和风暴潮发生的频率和强度增加。同时,由于长江流域水土保持和水库群建设,进入河口的泥沙量锐减,加剧了河口咸潮上溯,对区域人群生产生活产生一定影响。从全球气候变暖背景下长江口海平面上升和演变规律、长江口人类活动与气候变化影响下的动力要素变化、河口咸潮入侵时空分布和水盐交换机制及供水安全风险、海平面上升对海堤防洪御潮能力的影响、长江口地区防洪御潮韧性等5个方面总结归纳了现有研究成果,提出未来研究的方向,以期对保障河口地区水资源安全利用和防洪御潮能力提升提供参考。

钦江河口盐水入侵距离预测模型研究

平陆运河工程是中国“西部陆海新通道”的重要水运基础设施,青年枢纽作为运河最下游的节点性控制枢纽,受钦江感潮河段的盐水上溯的影响,合理预测盐水入侵距离对认识青年船闸寿命与城市饮用水安全具有重要意义。利用钦江河口盐水上溯过程的实测数据,基于盐水上溯一维扩散稳态方程构建了考虑河口几何形状、潮汐作用及径流过程的高潮期盐水入侵长度预测模型,并通过径流与潮汐作用对钦江河口盐水入侵长度的影响分析,取得的主要结论为:当径流流量Q<100 m^(3)/s时,平陆运河工程后的高潮位期钦江河口盐水入侵长度L=10~27 km,较工程前增加了4.5 km;当径流流量Q<20 m^(3)/s时,钦江河口盐水将上溯至青年船闸闸下;枯水期,当河口潮差H 0>2.5 m时,青年枢纽减盐的最低泄流量须达到20 m^(3)/s。

西北江三角洲河床变化对咸潮上溯影响的数值模拟研究

为研究西北江三角洲河床变化及其与咸潮上溯关系,收集整理以往研究成果资料与水文气象、河道地形数据的基础上,建立一维非恒定流含氯度数学模型,水动力和含氯度验证结果均满足相关规范要求,可以用于计算分析河床变化对咸潮上溯的影响。研究结果表明:①1999—2016年,西北江三角洲网河区河床处于不均匀下切状态,河道容积持续增大,导致河口涨落潮阻力减小,高盐水团沿河口上溯更为简单,咸潮上溯情势日益严峻;②各口门站的涨潮量增加,咸界上移取淡机率降低,思贤滘不同来流条件下,磨刀门水道咸界平均上移3735 m,平岗泵站的取淡机率平均减少5.33%,沙湾水道咸界平均上移2369 m,沙湾第一水厂取淡机率平均减少5.14%,严重影响河口地区的生态系统以及正常取水需求。研究结果可以为西北江三角洲及河口地区的供水安全保障措施研究及工程设计提供基础支撑。

船闸止水材料性能劣化规律试验研究

平陆运河河口船闸受咸水入侵及船闸闸室频繁灌泄水作用,形成了受紫外光照强、氯盐侵蚀及高频干湿交替共同影响的特殊腐蚀环境。然而,船闸止水材料在这一特殊服役环境下的性能劣化规律不甚明了。为此,文章开展了针对船闸止水材料在纯紫外老化环境、紫外老化与咸水高频干湿交替环境下的加速劣化试验,研究了四类橡胶止水带(包括:普通、OMEGA、GB、超高性能止水带)材料硬度、拉伸强度、断裂伸长率以及极限弹性模量随时间的劣化规律。结果表明:纯紫外老化环境下,四类橡胶止水带材料的硬度、极限弹性模量随劣化时间呈增大趋势,拉伸强度呈先增后减的变化趋势,断裂伸长率则单调减小;紫外老化与咸水高频干湿交替环境下,四类橡胶止水带材料的硬度、拉伸强度、断裂伸长率均随劣化时间呈减小趋势,极限弹性模量则单调增加。研究成果可为平陆运河河口船闸结构缝止水材料的优选类型提供重要参考依据。

辽河坳陷清水洼陷古近系沙河街组深层烃源岩特征及油气成藏模式

通过有机碳、岩石热解、氯仿沥青“A”、饱和烃色谱-质谱和流体包裹体等的分析,对辽河坳陷清水洼陷古近系沙河街组深层烃源岩特征和油气成藏模式进行了详细研究。研究结果表明:(1)辽河坳陷清水洼陷古近系沙河街组深层烃源岩主要发育在E2s32亚段、E2s33亚段和E2s4段,其中E2s32亚段Ⅱ小层泥岩最为发育,主要为深灰色厚层泥岩,整体厚度约170 m。(2)研究区深层烃源岩总有机碳质量分数平均可达1.60%,生烃潜量平均值为2.82 mg/g;有机质类型以Ⅱ1—Ⅲ型为主,主要为浮游植物与高等植物混合贡献,为弱氧化—弱还原的湖相咸水沉积环境;烃源岩有机质丰度为0.5%~1.5%,普遍达到大量生烃阶段,部分已达到高成熟演化阶段。(3)研究区深层烃源岩在距今38 Ma时进入生油窗,距今20 Ma时开始生成天然气;流体包裹体显示研究区存在2期油气充注,分别为38~26 Ma和20 Ma~现今,与生烃演化史匹配。