EFFECT ON ESTUARINE FINE-SEDIMENT TRANSPORT OF INTERMITTENT PUMP DISCHARGE AT PAGHAM HARBOUR, WEST SUSSEX

Field investigations were undertaken to identify the mechanisms of fine-sediment transport at a landward limit of Pagham Harbour. Which is a semi-enclosed natural harbour in West Sussex, UK. Measurements of water level, velocity, salinity and turbidity were made during three tidal cycles between June and August 2002. Near-bed measurements revealed that, for spring tides, the most significant transport occurs during the flood tide, with smaller turbidity peaks recorded at times of intermittent pumped discharges at low water. Vertical profiling revealed that the timing of these discharges acts as a control on the landward transport of fine sediment by increasing salinity stratification. The resulting graphs show that, while increased near-bed velocity leads to increased turbidity and sediment transport, the degree of vertical salinity gradient is also linked with landward transport of fine sediment. These results help to explain the role of tides and fresh-water flow in controlling the transport of fine sediment in natural harbours, emphasising the importance of taking stratification into account when using 2-D depth-averaged predictive numerical models.     

Reduction of fecal indicator bacteria (FIB) in the Ballona Wetlands saltwater marsh (Los Angeles County, California, USA) with implications for restoration actions

A benefit of wetland preservation and restoration is the ecosystem service of improving water quality, typically assessed based on bacterial loading. The Ballona Wetlands, a degraded salt marsh of approximately 100 ac located on the southern border of Marina Del Rey (Los Angeles County, California, USA) are currently the focus of publicly funded restoration planning. The wetlands receive tidal water, usually contaminated with fecal indicator bacteria (FIB: total and fecal coliforms, Escherichia coli, enterococci) from the adjacent Ballona Creek and Estuary. During the summer of 2007, two 24-h studies were conducted to determine FIB tidal dynamics within the wetland. Measurements of water flow and mean FIB concentrations (n = 3) were measured every 1.5 h to determine total FIB load estimates. FIB loading rates (MPN/s) were greatest during flood tides as water entered the wetlands, and then again during spring tide conditions when sediments were resuspended during swifter spring ebb flows. During daylight hours, the wetland acted as a sink for these bacteria as loads diminished, presumably by sunlight and other processes. Conversely, during late afternoon and night, the wetlands shifted to being a source as excess FIB departed on ebb flows. Therefore, the wetlands act as both a source and sink for FIB depending on tidal conditions and exposure to sunlight. Future restoration actions would result in a tradeoff - increased tidal channels offer a greater surface area for FIB inactivation, but also would result in a greater volume of FIB-contaminated resuspended sediments carried out of the wetlands on stronger ebb flows. As levels of FIB in Ballona Creek and Estuary diminish through recently established regulatory actions, the wetlands could shift into a greater sink for FIB.     

Flow measurement with multi‐instrumentation in a tidal‐affected river

Flow measurements in a tidal‐affected river provide important information of cyclic flow pattern characteristics in temporal and spatial variations. Reliability and accuracy of measured flow data can provide for numerical model calibration and verification. In the present study, we measured tidally affected river flow in the Danshui River of northern Taiwan during the 2008 summer and fall. The measured flow data, produced by both state of the art and conventional instruments including particle tracking velocimetry (PTV), acoustic Doppler profiler (ADP), horizontal acoustic Doppler current profiler (H‐ADCP) and Price‐type current metre (PCM) were compared and correlated during several tidal cycles. The mean flows by ADP were similar to that by PCM and highly correlated with those by PTV and H‐ADCP. Index velocity rating between ADP and H‐ADCP separately computed during the flood and ebb tides shows good correlation for the ebb tide and poor correlation for the flood tide due to subsurface maximum velocity in the middle‐ to near‐bottom layers.     

海潮影响区抽水试验静止水位取值的探讨

滨海地区地下水受潮汐影响而波动,在该地区进行抽水试验,其静止水位取值是一个难点.本文以宁波市蛇蟠涂围垦区S1号孔抽水试验为例,通过建立孔内地下水与潮水的峰谷值水位联动关系,利用易获取的潮水位峰、谷值数据来推算地下水位的峰、谷值,从而计算地下水的静止水位.研究表明,S1号孔内水位大致呈正弦曲线形态波动,与临近闸口的潮水位...     

Modelling Escherichia coli concentrations in the tidal Scheldt river and estuary

Recent observations in the tidal Scheldt River and Estuary revealed a poor microbiological water quality and substantial variability of this quality which can hardly be assigned to a single factor. To assess the importance of tides, river discharge, point sources, upstream concentrations, mortality and settling a new model (SLIM-EC) was built. This model was first validated by comparison with the available field measurements of Escherichia coli (E. coli, a common fecal bacterial indicator) concentrations. The model simulations agreed well with the observations, and in particular were able to reproduce the observed long-term median concentrations and variability. Next, the model was used to perform sensitivity runs in which one process/forcing was removed at a time. These simulations revealed that the tide, upstream concentrations and the mortality process are the primary factors controlling the long-term median E. coli concentrations and the observed variability. The tide is crucial to explain the increased concentrations upstream of important inputs, as well as a generally increased variability. Remarkably, the wastewater treatment plants discharging in the study domain do not seem to have a significant impact. This is due to a dilution effect, and to the fact that the concentrations coming from upstream (where large cities are located) are high. Overall, the settling process as it is presently described in the model does not significantly affect the simulated E. coli concentrations.     

Colour and turbidity removal with reusable magnetic particles—II. coagulation with magnetic polymer composites

Composite particles containing magnetic iron oxides in an insoluble polymeric matrix were used to enhance the coagulation of a turbid, coloured river water. Uncharged magnetic particles increased the turbidity removal at a given alum dose, or alternatively achieved a desired level of turbidity removal at a lower alum dose. Rates of floc formation and settling were approximately double those obtained with alum alone. Grafting linear polymers to the magnetic particles increased their effectiveness. The uncharged particles could be reused after simply washing with water. Magnetic particles with grafted chains of cationic polymers, when used in conjunction with alum, gave excellent removal of colour and turbidity and rapid settling, but required brine for regeneration. These materials were also effective in coagulating algae. When used in high doses without alum, the cationic magnetic particles initially gave good turbidity and colour removal from river water, but could not be completely regenerated     

Characterization of turbidity in Florida's Lake Okeechobee and Caloosahatchee and St. Lucie Estuaries using MODIS-Aqua measurements

This paper describes the use of ocean color remote sensing data from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite to characterize turbidity in Lake Okeechobee and its primary drainage basins, the Caloosahatchee and St. Lucie estuaries from 2002 to 2010. Drainage modification and agricultural development in southern Florida transport sediments and nutrients from watershed agricultural areas to Lake Okeechobee. As a result of development around Lake Okeechobee and the estuaries that are connected to Lake Okeechobee, estuarine conditions have also been adversely impacted, resulting in salinity and nutrient fluctuations. The measurement of water turbidity in lacustrine and estuarine ecosystems allows researchers to understand important factors such as light limitation and the potential release of nutrients from re-suspended sediments. Based on a strong correlation between water turbidity and normalized water-leaving radiance at the near-infrared (NIR) band (nL_w(869)), a new satellite water turbidity algorithm has been developed for Lake Okeechobee. This study has shown important applications with satellite-measured nL_w(869) data for water quality monitoring and measurements for turbid inland lakes. MODIS-Aqua-measured water property data are derived using the shortwave infrared (SWIR)-based atmospheric correction algorithm in order to remotely obtain synoptic turbidity data in Lake Okeechobee and normalized water-leaving radiance using the red band (nL_w(645)) in the Caloosahatchee and St. Lucie estuaries. We found varied, but distinct seasonal, spatial, and event driven turbidity trends in Lake Okeechobee and the Caloosahatchee and St. Lucie estuary regions. Wind waves and hurricanes have the largest influence on turbidity trends in Lake Okeechobee, while tides, currents, wind waves, and hurricanes influence the Caloosahatchee and St. Lucie estuarine areas.     

Stratification and fine sediment transport mechanisms in a semi-enclosed tidal lagoon (Pagham Harbour, West Sussex)

Preliminary analysis of data collected at a macrotidal semi‐enclosed lagoon (Pagham Harbour, UK) has revealed useful information about long‐term patterns of siltation and some of the related mechanisms. Sediment surface‐level measurements made over 2 years at different sites within Pagham Harbour have shown a steady siltation, in common with earlier measurements, which is moderated by seasonal effects due to erosion by locally generated waves. Furthermore, inspection of vertical profiles of salinity and turbidity over individual tidal cycles has revealed that the degree of sediment transport on the flood tide is related to the vertical salinity gradient. Thus, at the Ferry Pool site, which is characterised by episodic pumped discharges from a nearby sewage treatment plant, landward sediment transport is enhanced by the high degree of salinity stratification observed during the flood tide. The mobility of the sediment, and the greater distribution of softer, less well‐consolidated sediment deposits, is greater here than at the other significant freshwater inflow at the Salthouse site, where the fresh water flow is instead moderated by a tidal flap gate. Preliminary analyses suggest that the higher the salinity stratification, the greater the landward sediment transport during the flood tide. Such analyses could help inform future policy on the methods of land drainage to macrotidal lagoons, and on the potential for managed realignment at such sites.     

潮汐对跨海峡隧道衬砌稳定性影响研究

 厦门海底隧道是我国目前修建的最长的海底隧道,隧道及两岸接线工程位于福建省厦门地区。该地区潮汐现象多样,水文条件复杂,历年最大潮差达6.92 m,多年平均潮差4.01 m,在计算过程中应该考虑潮汐的影响。利用厦门海洋工程勘测中心的海流监测数据,考虑潮汐荷载循环变化过程中衬砌的疲劳损伤过程,用有限元方法模拟分析应力渗流耦合作用下隧道潮汐荷载对隧道衬砌和围岩稳定性的影响,研究成果对海峡海底隧道修建工程有所借鉴。     

Method for quantitative analysis of flocculation performance

The sedimentation rate and the post-sedimentation residual turbidity of flocculated suspensions are properties central to the design and operation of unit processes following flocculation in a water treatment plant. A method for comparing flocculation performance based on these two properties is described. The flocculation residual turbidity analyzer (FReTA) records the turbidity of flocculent suspensions undergoing quiescent settling. The fixed distance across which flocs must travel to clear the measurement volume allows sedimentation velocity distributions of the flocculent suspension to be calculated from the raw turbidity data. By fitting the transformed turbidity data with a modified gamma distribution, the mean and variance of sedimentation velocity can be obtained along with the residual turbidity after a period of settling. This new analysis method can be used to quantitatively compare how differences in flocculator operating conditions affect the sedimentation velocity distribution of flocs as well as the post-sedimentation residual turbidity.     

Neural network modeling of salinity variation in Apalachicola River.

Salinity is an important indicator for water quality and aquatic ecosystem in tidal rivers. The increase of salinity intrusion in a river may have an adverse effect on the aquatic environment system. This study presents an application of the artificial neural network (ANN) to assess salinity variation responding to the multiple forcing functions of freshwater input, tide, and wind in Apalachicola River, Florida. Parameters in the neural network model were trained until the model predictions of salinity matched well with the observations. Then, the trained model was validated by applying the model to another independent data set. The results indicate that the ANN model is capable of correlating the non-linear time series of salinity to the multiple forcing signals of wind, tides. and freshwater input in the Apalachicola River. This study suggests that the ANN model is an easy-to-use modeling tool for engineers and water resource managers to obtain a quick preliminary assessment of salinity variation in response to the engineering modifications to the river system.     

The impact of rainstorm events on coagulation and clarifier performance in potable water treatment

This paper examines turbidity removal at a water treatment works in England that receives raw water which is difficult to treat during certain rainstorm events. Rainstorm events lead to elevated levels of turbidity and organic matter found in river waters. A robustness index based on settled turbidity was used to identify periods and events that adversely affected the treatment process. This coupled with raw water sampling data indicated that a change in nature and an increase in natural organic matter (NOM) concentrations occurred following rainstorm events. Experimental work investigated the effect of temperature and NOM on the coagulation process and the results show how increasing levels of NOM significantly impaired the coagulation of particulate material, leading to an increase in settled turbidity.     

Flocculation of kaolinite suspensions in water by chitosan

Flocculation of kaolinite suspensions in water using chitosan was studied in the pH range 5-9 and the turbidity ranging from 10 to 160 NTU. Chitosan, in presence of trace quantities of a substance present in aqueous soil extracts, effectively reduces turbidity due to kaolinite by flocculation and settling. Flocculation efficiency is very sensitive to pH, and reaches a maximum at pH 7.5. The optimal chitosan concentration required to effect flocculation is independent of kaolinite concentration within the range examined. Flocculation is faster at higher concentrations of kaolinite and the flocs are large and settle rapidly.     

辐流沉淀池混凝剂投加参照曲线的绘制及应用

根据辐流沉淀池近三年的单池负荷、原水浊度以及混凝剂投加量数据,绘制了混凝剂投加量与浊度、单池负荷之间的曲线关系图,并介绍了混凝剂投加曲线的应用,以期对现实生产起指导作用。     

Variation in river water temperatures in an upland stream over a 30-year period

Stream water temperature data from the Girnock burn, a 30-km2 catchment in Scotland were examined for systematic variation across 30 years of record (1968-1997). The data suggest that there has been no change in mean annual temperature with time, but at a seasonal level there is some indication of an increase in mean daily maximum temperatures during the winter (December to February) and spring (March to May) seasons. For the spring season, there is also evidence that mean temperature has increased. There are no apparent or obvious changes in stream flow to account for this. The strong relationship between air and stream temperatures (r2 = 0.96) implies that changes in the stream are the result of changes in the climate. It is possible that this may occur as a result of the effect of increasing air temperatures which may have also reduced the influence of snow and snowmelt on the catchment during the winter and spring seasons.     

水平管沉淀新技术在水厂改造中的工程应用

针对斜管沉淀池出水浊度高、跑矾的问题,采用专利技术"高效絮凝塔"改善反应絮凝效果,采用专利技术"水平管沉淀技术"改造斜管沉淀池,成功地将淮安市东方自来水公司三期老水厂的处理水量由2.0×104m3/d提升到4.5×104m3/d,沉淀池出水浊度<3 NTU,降低了滤池的过滤负荷,改善了出厂水水质。该工程应用是老水厂改造方式的一次重大突破。     

Levels of heavy metals in the tidal Elbe and its estuary and the heavy metal input into the sea

Surface water samples were collected during missions in 1977, 1978, 1980 and 1983 at different sampling stations along the tidal Elbe, from river km 632 downstream from Hamburg to the outer end of the estuary. Special care was taken to minimize contamination during sampling, handling and analysis. Within the tidal Elbe five distinct zones of substantial anthropogenic heavy metal pollution inputs can be detected. An attempt is made to define anthropogenic background levels, which are extremely low for the dissolved trace metals Cd and Pb; 35 and 65 ng/kg, respectively. The level of dissolved Cu is 2200 ng/kg. Total baseline levels of Cd, Pb and Cu are, respectively, 120, 2500 and 4200 ng/kg. In the five river zones affected by anthropogenic trace metal inputs, distinctly larger maximum levels can occur. They decrease to the background values after mixing with the main water body. More elevated levels caused by re-suspension in the mixing zone with maximum turbidity can be assumed. Nickel and Co data are from one mission only. The order of magnitude of the trace metal input from the Elbe into the sea is evaluated.     

基于河流动态自然过程的生境修复策略

全球气候变化和土地利用方式的改变对河流的动态自然过程带来不利影响。而目前人们对河流的修复重治理效果而轻自然过程,特别是风景园林与相关学科的交叉与融合研究较少,缺乏聚焦中、微尺度基于河流动态自然过程的生境恢复方法指导。基于此,从雨洪淹没、潮汐消落的河流动态自然过程规律着眼,提出对应的生境修复策略：1)恢复水陆边界的自然属性,重建泛洪区和河岸的联系;2)梯度式快速恢复近自然河岸带生境植被;3)连通感潮河涌湿地和营建关键生物生境,实现多种共生生物栖息地的再生。该方法有助于恢复河流长期、稳定的自由流动,生境在河流动态潮汐作用下异质性不断提高,从而提高河流湿地的生物多样性,还能为城市中心的居民提供亲近自然的休闲空间,以期在河流生境修复实践方面为风景园林和多学科融合提供新思路。     

V形斜板强化接触絮凝沉淀设备的研发与应用

V形斜板强化接触絮凝沉淀技术利用设备的流体上升流道截面差造成水流沿重力方向的速度差,使斜板沉淀单元内部形成一定厚度的具有自我更新能力的絮体动态悬浮层,同时通过增设的垂直板来增加絮体悬浮层厚度,实现强化接触絮凝、提高絮体沉淀分离性能的目的.中试结果表明,当斜板长为850 mm、斜板间距为25 mm、直板长为150 mm时,沉淀设备达到最佳性能;在处理水量超过设计负荷的20%时,设备仍运行效果良好.在水厂改造项目中,V形斜板沉淀设备的出水浊度稳定在0.4 NTU以下,低于原设备的出水浊度(1.63 NTU),同时节省了49%的投药量.     

Climate change induced salinisation of artificial lakes in the Netherlands and consequences for drinking water production

In this paper we present a modelling study to investigate the impacts of climate change on the chloride concentration and salinisation processes in two man-made freshwater lakes in the Netherlands, Lake IJsselmeer and Lake Markermeer. We used a transient compartmental chloride and water balance model to elucidate the salinisation processes occurring under present conditions and assess future salinisation under two climate forcing scenarios. The model results showed that the Rhine River is the dominant determinant for the chloride concentration in both lakes, followed by drainage of brackish groundwater from the surrounding polders. The results further show that especially during dry years, seawater intrusion through the tidal closure dam is an important source of chloride to Lake IJsselmeer. The results from the climatic forcing scenarios show that Lake IJsselmeer is especially vulnerable to climate-induced salinisation whereas effects on Lake Markermeer are relatively small. Peak chloride concentrations at the raw water intake of the Andijk drinking water facility on Lake IJsselmeer are projected to increase to values above 250 mg/l in the most far-reaching climate change scenario W+ in 2050 for dry years. This is well above the maximum allowable concentration of 150 mg/l for chloride in drinking water.Modelling showed that climate change impacts the chloride concentrations in a variety of ways: 1) an increasing occurrence of low river flows from summer to autumn reduces the dilution of the chloride that is emitted to the Rhine with a constant load thereby increasing its concentration; 2) increased open water evaporation and reduced rainfall during summer periods and droughts increases the chloride concentration in the water; and 3) rises in sea level increase seawater intrusion through the tidal closure dam of Lake IJsselmeer. The processes described here are likely to affect many other tidal rivers or lakes and should be considered when planning future raw water intake stations for drinking water production or agricultural water supply.