Several significant hydrographic characteristics and their formation mechanism in the South China Sea during the spring and summer of 1998

dOn the basis of the CTD data obtained by the two cruises before and after summer monsoon burst (25th May, 1998), several significant hydrographic characteristics, their variation and formation mechanism in the South China Sea (SCS) are analyzed. The results show that the Kuroshio water intrudes into the SCS in the form of loop current, and its main part is limited to the east of 118degreesE near the Luzon Strait. Then it continuously extends westwards under the influence of the large-scale circulation, and has a distinct impact on the area north of 16degreesN. There are two high temperature and low salinity regions: west off Luzon and east off Vietnam respectively. One region west off Luzon strengthens obviously after summer monsoon burst, the other east off Vietnam shows a tendency of weakening in the north and strengthening in the south. The formation of these two high temperature and low salinity regions is related to the anti-cyclonic eddies existing in this area, besides, it is also related to the high temperature feature west of Luzon, the influx of Sulu Sea water and the influence of the large-scale air circulation. There is a cold region below the depth of 50 m in the south of Zhongsha Islands, and it strengthens after monsoon burst. The formation of cold water is related to the upwelling there.

Advances in Studying Oceanic Circulation from Hydrographic Data with Applications in the South China Sea

Methods for studying oceanic circulation from hydrographic data are reviewed in the context of their applications in the South China Sea. These methods can be classified into three types according to their different dynamics as follows: (1) descriptive methods, (2) diagnostic methods without surface and bottom forcing, and (3) diagnostic methods with the above boundary forcing. The paper discusses the progress made in the above methods together with the advancement of study in the South China Sea circulation.

Hotspots of seabirds and marine mammals between New Zealand and the Ross Gyre:importance of hydrographic features

This article is part of our long-term study on the quantitative at-sea distribution of the marine "upper trophic levels"—seabirds and marine mammals—in polar ecosystems, aiming at quantifying the factors influencing their distribution as well as detecting possible spatial and temporal changes, with special attention to hydrography and to global climate changes. During an expedition of icebreaking RV Polarstern in February 2010, along the North–South transect between New Zealand and the Ross Gyre, off the Ross Sea, 3200 seabirds belonging to 22 identified pelagic species were recorded during 338 half-hour transect counts. Four major hotspots were identified. These were in Sub-tropical Water off New Zealand(up to 300 birds per count), and at the main Southern Ocean fronts: the Sub-Antarctic Front(up to 240 per count), the Antarctic Front(up to 150 per count) and the Polar Front(up to 200 per count), representing the vast majority of recorded seabirds. The most numerous species in the three frontal zones were: prions—mainly slender-billed Pachyptila belcheri—and Salvin’s albatross Thalassarche [cauta]salvini. The eight more abundant species represented 2650 birds, i.e. more than 80% of the total. A random forest clustering method identified four groups of seabird species occupying similar oceanographic niches.

Spectrum Characteristics and Transfer Function of the Hydrograph of the Deep Aqueous System

The fluctuation of most of the hydrograph in the deep aqueous system records the fluid pulsation in lithosphere and variation of the earth's crust. Many observations have verified that groundwater is an ideal information carrier of the crust. In this paper, the series of input (precipitation, air pressure, Earth tide etc.) and output (water level, artesian flow) of the deep aqueous system are studied by using the spectrum analysis and system theory. The application concepts of transfer function and the spectral structure of the hydrograph enrich the knowledge of the deep aqueous system. Two typical spectral structures of the hydrograph of the deep aqueous system are obtained by comparing with many water-bearing systems of the Jizhong depression. One is from well Ma-17 and the other is from the well Xinze-5. Finally, the physical models of forming the spectrum of the hydrograph are constructed on the basis of the spectrum research on the deep aqueous system.

Hydrographic characteristics and its variation of the South China Sea before and after monsoon burst in 1998

The differences of temperature, salinity distribution characteristics and structure of circulation in the upper layer of the South China Sea (SCS) are analyzed, based on the CTD and ADCP data from the two intensive surveyed cruises (IOP1: April 10 - May 5; IOP2: June 12 - July 6) and carried out before and after the Asian monsoon burst (May 25) during the South China Sea Monsoon Experiment (SCSMEX) in 1998. The results showed that field of temperature in the upper layer of the SCS distinctly changed before and after the monsoon burst, the average surface temperature increased by 0.75℃ , with its influence down to the depth of 500 m. The interaction of the local circulation in some areas resulted in the complexity and variability of the temperature and salinity structure in the upper layer, and the alternating distribution of cold and warm water regions (blocks). The high salinity subsurface water obviously intruded into the SCS from the Northwest Pacific, but only limited to the area of southwest of Taiwan Island, and the low salinity intermediate water flowed from the SCS to the Northwest Pacific. The circulation field of the SCS in the summer mainly consisted of cyclonic and anticyclonic eddies (rings). With the burst of the monsoon, the intensity and amount of the anticyclonic or the cyclonic eddies (rings) would vary, showing the complex distribution patterns and variations. The result analyzed by the isopycnic surface method coincided extremely with those by in situ survey (ADCP), which showed that the formation of circulation in the SCS was mainly controlled by the internal mass field, that is, dominated by the geostrophic component.

Hydrographical parameters and phytoplankton assemblages along the Pondicherry—Nagapattinam coastal waters,southeast coast of India

Hydrographical parameters and phytoplankton assemblages were determined along the Pondicherry, Parangipettai and Nagapattinam coastal waters, southeast coast of India. All the hydrographical parameters such as sea surface temperature, salinity, p H, total alkalinity, dissolved oxygen and nutrients like nitrate, nitrite, inorganic phosphate and reactive silicate, chlorophyll a and phytoplankton assemblages were studied for a period of five months(May, August, September 2010, March and November 2011). Over 121 species of phytoplankton represented by 93 species of diatoms, 16 species of dinoflagellates, 9 species of blue-green algae, 2 species of greens and 1 species of silicoflagellate were recorded. High phytoplankton species diversity was found in March 2011 when salinity and nitrate concentrations were low and reactive silicate and inorganic phosphates were moderate. Species diversity was low during May 2010 when increased sea surface temperature, salinity and low nutrients availability were observed. Coscinodiscus centralis, Diatoma vulgaris and Proboscia alata were dominant, especially Coscinodiscus sp. distributed in all stations whereas Skeletonema costatum, Odontella sinensis and Ditylum brightwellii were abundant in August and September 2010. From principal component analysis and multiple regression analysis, it is evident that variables like sea surface temperature and dissolved oxygen are the most important factors influencing the seasonal pattern of phytoplankton population.

Hydrographic structure and circulation in the central area of the North Eastern Atlantic

-On the basis of the hydrographic data observed within the Canary Basin in autumn 1985, temperature-salinity properties, distributions of water masses and barocltne flow field, as well as the volume transports in this area are described more detailly. The analyses indicate that the activity in the waters of the Canary Basin is mainly attributed to the interleaving and mixing between the originated water masses (e. g. Surface Water, North Atlantic Central Water, Mediterranean Water and Deep Water) and the modified water masses (Subpolar Mode Water, Labrador Sea Water and Antarctic Intermediate Water) from the outside of the study area and the variation of themselves. The east recirculation of the Subtropic Gyre in the North Atlantic consists of Azores Current and Canary Current.Azores Current is formed with several flow branches around the Azores Island, while the main flow lies at 35?N south of the Azores Island. It begins to diverge near the 15?W. The return flow found off the Portugal coast may be its northern branch. The southern invasion of the Labrador Sea Water and the Subpolar Mode Water are prevented by Azores front which serves an obvious boundary separating the North Western Atlantic (Central) Water and the North Eastern Atlantic (Central) Water.

Establishing a Hydrographic Framework for Watershed Management across Northern Chile

This article demonstrates how currently available digital elevation (NASA SRTM;30 m resolution) and hourly global precipitation data (rain, snow;5 and 10 km resolution) can be used to hydrographically quantify the regional watershed management context across northern Chile. This is done through comprehensive derivations of flow direction, flow accumulation, flow channels, floodplain extent, depressions, and upslope watershed outlines. In turn, these derivations allow for estimating potential precipitation accumulations within any watershed, and turn these into subsequent storm-averaged discharge estimates at, e.g., at any road—flow-channel crossing points. This article elaborates on this by modelling and mapping hydrological conditions and subsequent storm damage at the regional scale and at select locations in terms of recent flood events on March 2015, May 2017, and June 2017. It was found that modelled flood extent and storm-estimated discharge volumes and rates generally conform to reported values including storm-caused damages within communities along the Huasco, Elqui, Limari, Copiapó and Salado rivers. This included the storm response assessment of six water reservoirs as these varied, as quantified, from normal (Puclaro, La Laguna, Cogoti), at capacity (La Paloma, Cogoli), and overflowing (Recoleta). The details of the local to regional assessments are presented in the form hydrologically explicit maps, figures and tables. Together, these attest to the general validity of the framework as introduced. Hydrometrically based stream-discharge calibrations would assist in further refining the approach, especially in terms of estimating local to regional run-off coefficients.

An Integrated Approach to Hydrographic Surveying of Large Reservoirs—Application to Tarbela Reservoir in Pakistan

Hydrographic surveying in reservoirs is a key activity in order to collect data for a variety of purposes like estimation of storage capacity, rate and pattern of sediment deposition, movement of underwater sediment delta and reservoir routing, etc. These parameters play a pivotal role in any planning, management and operation activity of the reservoirs. Traditional approaches to perform hydrographic surveying in Indus Basin are time consuming, laborious, comparatively inaccurate and costly. As water resources are under immense pressure due to a variety of factors, such inefficient methods are not acceptable for efficient water management. In this study, an integrated approach for hydrographic surveying is introduced and evaluated in terms of its efficiency in comparison with the traditional methods of hydrographic surveying. The approach develops an integrated environment of hydrographic surveying comprising human, hardware and software. The process of surveying starts from in-house planning using specialized geo-spatial softwares. Then, on site a combination of computer hardware, echosounder, differential global positioning system (DGPS), survey vessel and survey crew is made. Post-processing is performed after conducting a survey in order to improve quality of data by filtering errors and producing the end product like reservoir underwater terrain, development of reservoir stage-area and stage-storage relationships, etc. The study was applied to Tarbela Reservoir, Pakistan.

THE HYDROGRAPHIC FEATURES OF THE OCEAN REGION AROUND THE RYUKYU ISLANDS DURING SUMMER OF 1997

Study of CTD data collected by the R/V DONG FANG HONG 2 in a 1997 summercruise in the ocean region around the Ryukyu Islands showed: 1) the existence, in the upper layer, of ahigh salinity water (HSW) core at about 200 dbar, and a low salinity water (LSW) core, centered atabout 700 dbar on the Pacific Ocean side of the Ryukyu Ridge, and located shallower on the East Chinafor (ECS) side; 2) the existence, in the upper layer, of warm water regions (WWR) west of Amami Is-land and Ishigaki Island, and a cold water region (CWR) east of Okinawa Ieland; in the lower layer, ofa CWR (WWR) southwest (southeast) of Okinawa Island; 3) the intrusion of North Pacific IntermediateWater into the ECS through the Kerama Trench located south of Okinawa Island and the strait east of Tai-wan Island.

Lineament Mapping in Batie Area(West-Cameroon)Using Landsat-9 Operational Land Imager/Thermal Infrared Sensor and Shuttle Radar Topography Mission Data:Hydrogeological Implication

This study focuses on the mapping of lineaments using remote sensing techniques and Geographic Information Systems.The aim is to carry out a statistical analysis of the lineaments in order to better understand the organization of fracturing in the Batie district,and to identify areas of high fracturing density and their relationship with the hydrographic network.The methodology implemented to achieve these objectives is based on the processing and analysis of Landsat 9 Operational Land Imager/Thermal Infrared Sensor(OLI/TIRS)satellite imagery and Shuttle Radar Topography Mission(SRTM)data covering the study area.After essential pre-processing of data,the following processing techniques were applied:Principal Component Analysis,Sobel Directional Filter with a 3×3 matrix and shaded relief of SRTM data with a sun azimuth of 345°,altitude of 45 m and an elevation factor of 3,followed by manual lineament extraction.The results reveal a total of 176 lineaments,ranging in size from 0.002 to 2.461 km,with an average length of 840.66 km.The projection of these lineaments on a Rose diagram shows a predominance of the North East–South-West(NE-SW)direction,which is the direction of the major tectonic fractures that affect the basement of Central Africa.These lineaments are organized into networks and corridors that define large fracture zones or corridors that control the drainage of the study area.The zones with networks show medium and high densities.This fracturing density gives good aquifer and reservoir potential to the study area.

Estimation of Groundwater Recharge Using Water Table Fluctuation Method in Bamako and Surrounding Areas, Mali

Bamako’s geographic and demographic expansion is sure to increase the need for water, and the slow development of the water supply network seems unable to meet this need. The knowledge of the approximate quantity of water reaching the groundwater is crucial, given the high dependence of this city and its surrounding area on groundwater. The aim of this study is to estimate the average groundwater recharge on a monthly scale, based on measurements taken over a 24-month period by using Water Table Fluctuation (WTF). The monthly recharge values obtained from the 15 piezometers in the study area by using WTF method vary from 1.04 to 38.81 mm with an average value of 9.74 mm. As part of the precipitations, these values represent respectively 1.29%, 48.52% and 12.17% of monthly average precipitation. It appears in this study that despite the piezometers belonging to the same climatic zone, the recharge rate can be different because of many factors such as the thickness of the aquifers, the soil and geology type, the local land cover and land use activities.

The winter western boundary current of the South China Sea:physical structure and volume transport in December 1998

The unique survey in December 1998 mapped the entire western boundary area of the South China Sea（SCS）,which reveals the three-dimensional structure and huge volume transport of the swift and narrow winter western boundary current of the SCS（SCSwwbc） in full scale. The current is found to flow all the way from the shelf edge off Hong Kong to the Sunda Shelf with a width around 100 km and a vertical scale of about 400 m. It appears to be the strongest off the Indo-China Peninsula, where its volume transport reached over 20×10~6 m^3/s. The current is weaker upstream in the northern SCS to the west of Hong Kong. A Kuroshio loop or detached eddy intruded through the Luzon Strait is observed farther east where the SCSwwbc no more exists. The results suggest that during the survey the SCSwwbc was fed primarily by the interior recirculation of the SCS rather than by the＂branching＂ of the Kuroshio from the Luzon Strait as indicated by surface drifters, which is likely a near-surface phenomenon and only contributes a minor part to the total transport of the SCSwwbc. Several topics related to the SCSwwbc are also discussed.

Analysis of Runoff in Ungauged Mountain Watersheds in Sichuan,China using Kinematic-wave-based GIUH Model

Floods are one of the most common natural hazards occurring all around the world.However,the knowledge of the origins of a food and its possible magnitude in a given region remains unclear yet.This lack of understanding is particularly acute in mountainous regions with large degrees in Sichuan Province,China,where runoff is seldom measured.The nature of streamflow in a region is related to the time and spatial distribution of rainfall quantity and watershed geomorphology.The geomorphologic characteristics are the channel network and surrounding landscape which transform the rainfall input into an output hydrograph at the outlet of the watershed.With the given geomorphologic properties of the watershed,theoretically the hydrological response function can be determined hydraulically without using any recorded data of past rainfall or runoff events.In this study,a kinematic-wave-based geomorphologic instantaneous unit hydrograph (KW-GIUH) model was adopted and verified to estimate runoff in ungauged areas.Two mountain watersheds,the Yingjing River watershed and Tianquan River watershed in Sichuan were selected as study sites.The geomorphologic factors of the two watersheds were obtained by using a digital elevation model (DEM) based on the topographic database obtained from the Shuttle Radar Topography Mission of US's NASA.The tests of the model on the two watersheds were performed both at gauged and ungauged sites.Comparison between the simulated and observed hydrographs for a number of rainstorms at the gauged sites indicated the potential of the KW-GIUH model as a useful tool for runoff analysis in these regions.Moreover,to simulate possible concentrated rainstorms that could result in serious flooding in these areas,synthetic rainfall hyetographs were adopted as input to the KW-GIUH model to obtain the flow hydrographs at two ungauged sites for different return period conditions.Hydroeconomic analysis can be performed in the future to select the optimum design return period for determining the flood control work.

Improved PSO algorithm based on chaos theory and its application to design flood hydrograph

The deficiencies of basic particle swarm optimization （bPSO） are its ubiquitous prematurity and its inability to seek the global optimal solution when optimizing complex high-dimensional functions. To overcome such deficiencies, the chaos-PSO （COSPSO） algorithm was established by introducing the chaos optimization mechanism and a global particle stagnation-disturbance strategy into bPSO. In the improved algorithm, chaotic movement was adopted for the particles＇ initial movement trajectories to replace the former stochastic movement, and the chaos factor was used to guide the particles＇ path. When the global particles were stagnant, the disturbance strategy was used to keep the particles in motion. Five benchmark optimizations were introduced to test COSPSO, and they proved that COSPSO can remarkably improve efficiency in optimizing complex functions. Finally, a case study of COSPSO in calculating design flood hydrographs demonstrated the applicability of the improved algorithm.

A Dam Break Analysis Using HEC-RAS

This paper firstly described the dam break in the aspects of theories and models. Break parameters prediction, the understanding of dam break mechanics, peak outflow prediction were shown as the essential for the dam break analysis, and eventually determined the loss of the damages. Secondly, as an application example, Foster Joseph Sayers Dam break was further modeled and analyzed using USACE Hydrologic Engineering Center’s River Analysis System (HEC-RAS) model based on available geometry data. The results show that dam break is a complicated and comprehensive process involving lots of principles. Combination of mechanics and case studies, reflection of predominant mechanisms of headcut erosion, more specific categorization of dam, prudent investigation and inference of dam break process are needed in developing a satisfactory dam break simulation model. Foster Joseph Sayers Dam break due to piping elongates the time period of high water surface level, which increases the duration of risk. However, the dam break does not increase the downstream maximum water surface elevation (Max. W.S. Elev) significantly at previous design Probable Maximum Flood (PMF). Dam break has a greater impact on the downstream location where is closer to the dam in accordance with the comparison of the hydrographs at different downstream locations. Sensitivity analysis demonstrates that the changes of dam break parameters had no much influence on the downstream Max. W.S. Elev.

Calibration of HEC-RAS Model on Prediction of Flood for Lower Tapi River, India

Channel roughness is a sensitive parameter in development of hydraulic model for flood forecasting and flood inundation mapping. The requirement of multiple channel roughness coefficient Mannnig’s ‘n’ values along the river has been spelled out through simulation of floods, using HEC-RAS, for years 1998 and 2003, supported with the photographs of river reaches collected during the field visit of the lower Tapi River. The calibrated model, in terms of channel roughness, has been used to simulate the flood for year 2006 in the river. The performance of the calibrated HEC-RAS based model has been accessed by capturing the flood peaks of observed and simulated floods;and computation of root mean squared error (RMSE) for the intermediated gauging stations on the lower Tapi River.

Flash flood hazard mapping: A pilot case study in Xiapu River Basin, China

Flash flood hazard mapping is a supporting component of non-structural measures for flash flood prevention. Pilot case studies are necessary to develop more practicable methods for the technical support systems of flash flood hazard mapping. In this study, the headwater catchment of the Xiapu River Basin in central China was selected as a pilot study area for flash flood hazard mapping. A conceptual distributed hydrological model was developed for flood calculation based on the framework of the Xinanjiang model, which is widely used in humid and semi-humid regions in China. The developed model employs the geomorphological unit hydrograph method, which is extremely valuable when simulating the overland flow process in ungauged catchments, as compared with the original Xinanjiang model. The model was tested in the pilot study area, and the results agree with the measured data on the whole. After calibration and validation, the model is shown to be a useful tool for flash flood calculation. A practicable method for flash flood hazard mapping using the calculated peak discharge and digital elevation model data was presented, and three levels of flood hazards were classified. The resulting flash flood hazard maps indicate that the method successfully predicts the spatial distribution of flash flood hazards, and it can meet the current requirements in China.

APPROACH OF DETERMINISTIC GEOMORPH OLOGIC INSTANTANEOUS UNIT HYDROGRAPH TO HYDROLOGICAL PROCESSES' SIMULATION IN KARST AREA

In order to analyze the condition of s pecial landform and regularity of sp ecial hydrological movement in karst area,the method of Geomorphologic Instantaneous Unit Hydrograph(GIUH)has been used to divide the river net-works into three grades in the research area and the karst hydrologic processes were simulated with Nash insta ntaneous u-nit hydrograph(NIUH).The combination of the GIUH and NIUH fully considers the moving path of wa ter particles in drainage and the regional composition of runoff at the end of the drainage,resulting in a rational combinatio n of probabili-ty of GIUH and NIUH and geomorphologic parameters which could reflect the complexity of the landform structur e of karst drainage.The results showed t hat the combined method of GIUH and NI UH has clear physical concept and acc ept-able precision,which can be widely a pplied on hydrological studies of karst area.

Estimation of Small Reservoir Sedimentation in Semi-Arid Southern Zimbabwe

Small surface reservoirs play an important role of providing ready and convenient source of water for various uses in semi-arid areas which are characterized by erratic and low rainfall. Lack of current data on reservoir capacity loss due to sedimentation is one of the challenges to the sustainable management of surface reservoirs. The study investigated the capacity loss due to sedimentation from 2000-2012, and estimated the trap efficiency of the Mutangi reservoir which is located in semi-arid Chivi, Southern of Zimbabwe. Hydrographic surveys, grab sampling and water depth-capacity methods were used to determine the capacity of the dam as of 2012. To compute capacity loss from 2000 to 2012, the 2000 and 2012 dam capacities were compared whilst the trap efficiency of the reservoir was determined using a set of empirical models that relates trap efficiency to the capacity-watershed area ratio and capacity-inflow ratio. The results show that Mutangi reservoir has a trap efficiency of 95% - 98% (av = 96.4%) and has lost 37% of its capacity due to sedimentation in 12 years (2000 and 2012). Rates of sedimentation were 8539 t·yr-1, 9110?t·yr-1 and 8265 t·yr-1 for the hydrographic survey, grab sampling and water depth-capacity method respectively, and the little difference in these figures demonstrates that any method can be used to determine sedimentation rates. The area specific sediment yield (ASY) ranged from 14 - 15.5 t·ha-1·yr-1 (av = 14.956 t·ha-1·yr-1). At the current rate of sedimentation the projected dead level of the reservoir will be lost to sedimentation in 8 years while the useful life of the reservoir is estimated to be 30 years. Capacity loss due to sedimentation is further complicating the already strained water scarcity situation in semi-arid areas and management decisions should be made based on the current sedimentation rates estimated by different methods. These results imply that management practices that reduce erosion, hence sedimentation in these small reservoirs should be practiced in order to prolong their lifespan.