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.

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.

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.

Design Tide Hydrograph with A Given Risk Threshold by A Copula-Based Multivariate Method

This paper describes the development of a T-year design tide hydrograph （DTH）. A core innovation is that the proposed technique uses the design risk threshold and copula-based conditional risk probability to analyze the optimal combination of high waters and low waters of the DTH. A brief description of the method is presented. The in situ semi-diurnal tide data at the coast of Jiangsu Province in China are analyzed. Marginal distributions for high waters and low waters of tides are examined. Furthermore, the joint distributions, condition risk probabilities and risk thresholds of high waters and low waters are presented. Results of the DTH from the proposed method are compared with those from the traditional same-multiple enlarging design approach. It is demonstrated that the proposed method is preferable.

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.

Z-Transform Based Instantaneous Unit Hydrograph for Hilly Watersheds

Present study emphasizes the applicability of linear theory concept onto hilly watersheds. For this purpose, Z-transform technique was used to derive the instantaneous unit hydrograph (IUH) from the transfer function of autoregressive and moving average (ARMA) type linear difference equation. Parameters of the ARMA type rainfall-runoff process were estimated by least-squares method. The derived IUH from Z-transform (i.e. ARMA-IUH) has been used to compute the hydrologic response i.e. direct runoff hydrograph (DRH). Fur-ther, the superiority of the proposed approach has been tested by comparing the results through the results obtained from the Nash-IUH. Analyzing the results obtained from ARMA-IUH and Nash-IUH for the two hilly watersheds of North Western Himalayas shows the applicability of the linear theory concept even in turbulent flow conditions which are frequently encountered in hilly terrains under similar conditions of flow.

Physical modeling into outflow hydrographs and breach characteristics of homogeneous earthfill dams failure due to overtopping

The main objective of the present study is to introduce new empirical equations for the determination of breach geometrical dimensions and peak outflow discharge(Q_(p)).Therefore,a historic failure database of 109 embankments was collected and examined.The most important factors that affect the breach evolution,including grading size,hydraulic,and outflow characteristics are also studied.Some of the parameters used for the determination of Q_(p) and average breach width(Bave)have a significant effect on the erosion process,but they are less reflected in the technical literature.To study the behavior of noncohesive soils during overtopping,15 physical tests were performed at the laboratory,and the effects of interfering parameters were investigated.The experimental output hydrograph was used to simulate the hydrographs resulting from the failure of real dams,and recent artificial intelligence techniques along with linear and nonlinear regression models were employed.The area-time analysis of the laboratory hydrographs shows that the soil particle size and the characteristics of reservoir-basin significantly affect the rate of breach formation and outflow discharge.New relationships are introduced,based on the breach characteristics,by a combination of historical and experimental data,as well as case studies conducted on the hypothetical failure of 10 operational dams.The mathematical model is also used to simulate the process of breach evaluation.Based on statistical indices,comparison of the results,and sensitivity analysis,the developed equations can better express the susceptibility of materials to erosion and their application can minimize downstream vulnerabilities.

Time Step Issue in Unit Hydrograph for Improving Runoff Prediction in Small Catchments

Unit hydrograph is a very practical tool in runoff prediction which has been used since decades ago and to date it remains useful. Unit hydrograph method is applied in Way Kuala Garuntang, an ungauged catchment in Lampung Province, Indonesia. To derive an observed unit hydrograph it requires rainfall and water level data with fine time scale which are obtained from automatic gauges. Observed unit hydrograph has an advantage that it is possible to derive it for various time steps including those with time step less than an hour. In order to get a more accurate unit hydrograph, it is necessary to derive a unit hydrograph with small time step for a small catchment such as those used in this study. The study area includes Way Kuala Garuntang and its tributaries, i.e. Way Simpur, Way Awi with areas are 60.52 km2, 3.691 km2, and 9.846 km2 respectively. The results of this study highlight the importance of time step selection on unit hydrograph, which are shown to have a significant impact on the resulting unit hydrograph’s variables such as peak discharge and time to peak.

Isotope hydrograph separation in alpine catchments:a review

Isotope hydrograph separation （IHS） is a basic tool in applied hydrology. Its application has expanded to surface water and groundwater interaction, and eco-hydrological processes from runoff generation processes. This paper reviews the progress made in IHS for alpine catchments, with emphasis on its significance in reflecting the impact of global change on water resources. Also, the principle of IHS and its uncertainties are explained in detail. The mechanism of variation of stable isotopes in snow-melt water is discussed, and then methods are presented to improve the separation during snow-melt such as volume weighted average method （VWA）, current melt-water method （CMW） and runoff-corrected event water approach （RunCE）, with their advantages and disadvantages explained. New approaches may extend the applications of IllS, for example, large basin studies combined with GIS, and develop new theories of runoff generation combined with other pararneters such as deuterium excess and DOC.

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.

Developing GIS-Based Unit Hydrographs for Flood Management in Makkah Metropolitan Area, Saudi Arabia

Unit hydrographs (UH) are either determined from gauged data or derived using empirically-based synthetic unit hydrograph procedures. In Saudi Arabia, the discharge records may not be available either for several locations or for long time scales, and therefore synthetic unit hydrographs are crucial in flood and water resources management. Available metrological, geological, and land use datasets have been utilized in order to apply the US National Resources Conservative Services (NRCS) methodology in a Geographic Information Systems (GIS) environment. Furthermore, NRCS unit hydrographs have been developed for six watersheds within Makkah metropolitan area, southwest Saudi Arabia. The accomplished results show that the UH time to peak discharge vary from 1.15 hours to 4.47 hours, and the UH peak discharge quantities range from 10.14 m3/s to 16.74 m3/s. It is concluded that the third basin in Makkah city may be considered as the most hazardous catchment. Hence, it is recommended that careful flood protection procedures should be taken in this area within Makkah city.

End-Member Selection in Two-Component Isotope-Based Hydrograph Separation

The science that underpins our knowledge and understanding of Isotope-Based Hydrograph separation (IHS) has gained grounds, over the last few decades, in the identification of streamflow sources. However, challenges still exist in identifying appropriate tracers and the right combination of end-members for the IHS process. In a two-component IHS analysis, the application of the dual isotopes tracers, δ18O and (or) δ2H, is regarded as the simplest method. We undertook an IHS study within a nested system of eight Prairie watersheds located in South central Manitoba, Canada. The work evaluated about 17,000 results emanating from the application of a combination of two potential tracers (δ18O and δ2H) and eight each of potential “old” and “new” water end-members in a two-component IHS process. The outcome showed occurrences of many mathematically possible but hydrologically unacceptable IHS results. The observation was particularly predominant within relatively larger perennial sub-catchments of the watershed. It is also shown that inter-site sub-catchment isotopic end-member transferability is possible within watersheds of similar physio-hydrographic characteristics. We suggest that a careful evaluation of the physio-hydrographic characteristics of catchments be considered in IHS studies in addition to the recommended guidelines in the selection of tracers and end-members.

On Redefining the Onset of Baseflow Recession on Storm Hydrographs

Two methods that define the point of baseflow recession onset were compared using storm hydrograph data for 27 storm events that occurred between 1982-1995 in the Upeo watershed located in the Andes mountain range in central Chile (Figure 1). Three well-known baseflow recession equations were used to determine whether the method we are proposing here, that defines baseflow recession onset as the third inflection point on the logarithmic graph of the falling limb of the storm hydrograph, more accurately models observed data than the most widely used method that defines baseflow onset as the second inflection point on the same graph. Five time intervals were used to modify the recession coefficient in search of a more accurate fit. Results from the coefficient of determination, standard error, Mann-Whitney U test, and Bland-Altman test suggest that redefining baseflow recession onset via the proposed approach more accurately models baseflow recession behavior.

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.

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.

Analysis of Design Rainstorm Hydrograph Based on Asymmetrical Extreme Value Copula

In this paper,the maximum 1-hour rainfall( rain peak),the maximum 6-hour rainfall and the maximum 24-hour rainfall in the Caojiang River basin from 1967 to 2013 were taken as samples. The typical typhoon rainstorm hydrograph of joint distribution of rainfall in three periods was constructed based on the asymmetric Archimedean Gumbel-Hougaard extreme value Copula. The main conclusions were as follows:( 1) the design rainstorm value in the Caojiang River basin calculated by using the joint distribution of rainfall in three periods was larger than the design rainstorm value of the joint distribution in two periods and that of a single period. The design rainstorm process hydrograph amplified at the same frequency had the optimal overall effect,which provided a new idea and method for studying the design rainfall patterns.( 2) According to the maximum 24-hour rainfall,the risk rate of the multi-peak rainstorm process that the main peak was in the back was the highest,and the constructed typical design rainstorm process hydrograph was the most representative.( 3) " OR" joint return period of rainfall combination in three periods as the design criteria of a watershed was applicable to responding to the risk of rainfall and flood in this watershed.

Progress on the Use of Stable Isotope Techniques in Catchment Hydrograph Separation: A Review

Hydrograph separation is a fundamental catchment descriptor,revealing information about sources of water in runoff generation processes. The water isotopes are ideal tracers in studying hydrological processes since the isotope fractionation produces a natural labeling effect within the hydrologic cycle. The water isotope technique has become one of effective means for investigating complex hydrologic system on a catchment scale. This paper reviews the progress on the use of stable water isotope techniques in catchment hydrograph separation in last decades. Also,the isotope mixing model for hydrograph separation and its uncertainties are explained in detail. In future research,there are three hot issues in the use of isotopic hydrograph separation（ IHS） ： integrating new approaches into IHS,calibration and verification of IHS model and IHS application in large river basins.

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.