Turbidity dynamics in karstic systems. Example of Ribaa and Bittit springs in the Middle Atlas (Morocco)

Abstract

The identification of the turbidity mechanisms in two karstic springs (Ribaa and Bittit) located in the Middle Atlas Plateau in Morocco was performed by means of correlation and spectral analyses applied to time series of rainfall, flow rates, and turbidity. Time series analyses of rainfall and discharges revealed high inertia and storage capacities of the karstic systems. However, the occurrence of turbidity in the springs proved independent of discharges. A causal relationship between rainfall and the occurrence of turbidity in the form of waves was established. Accordingly, turbidity was assumed to be related to the hydrodynamic conditions prevailing in the karst. Turbulent quickflows in the karst transmissive conduits, following heavy rainfall, are thought to provoke the resuspension of solid particles deposited in the conduits, as well as their transport towards outlets. An external origin has also been contemplated, concerning infiltration waters may be loaded with suspended matters washed from the watershed.     

Study of hydro-sedimentary variability of the Radicatel karst system influenced by climate signal fluctuations (Normandy,France)

ABSTRACT

This study relies on the use and analysis of hydro-meteorological variables, long turbidity time series (from 1988 to 2009, 21 years) and a sedimentary record to provide better understanding of the hydro-sedimentary variability of the karst system near the town of Radicatel, France. Wavelet analysis of rainfall, piezometric level and turbidity, as well as the sediment archive, show common modes of variability. A common spectral composition emphasizes the influence of climate controls. Comparison of the wavelet spectra with the North Atlantic Oscillation (NAO) spectrum clearly highlights the control of the latter on hydro-meteorological variables at the regional level. Climatic fluctuations are recorded in the turbidity signal and in sedimentary fill, as revealed by the 5- to 8-year frequency band, which is characteristic of the NAO index. A climatic signal is recorded in both rainfall events and piezometric levels, and also in sediment transport and deposition at the scale of the local karst system. The overall climate control is also present beyond the local variations and heterogeneities.

EDITOR D. Koutsoyiannis ASSOCIATE EDITOR D. Yang     

Determining suspended sediment loads from turbidity records / La détermination des charges en suspension des rapports sur la turbidité

Abstract

The Pennsylvania Department of Transportation and the US Geological Survey are cooperating in several field studies to evaluate sediment control measures used during highway construction. Among the parameters being monitored are suspended sediment concentration and turbidity. Sediment loads are calculated from suspended sediment and water discharge data, but some sediment loads must be determined indirectly because it is virtually impossible to obtain sufficient suspended sediment samples to define all runoff conditions adequately. Sediment discharge-water discharge correlation curves have proved unreliable for streams affected by highway construction, so an alternative method using the turbidity record was developed during these studies.

The field data reveal a good correlation between daily mean discharge-weighted turbidity and daily mean discharge-weighted suspended sediment concentration. Turbidity is monitored and recorded continuously, and the daily mean discharge-weighted turbidity is calculated from the turbidity and water discharge data. During periods when there are insufficient suspended sediment data, the daily mean discharge-weighted suspended sediment concentration is determined from the turbidity-sediment correlation and used with the daily mean water discharge to calculate a daily sediment load.

This method of determining sediment loads from the turbidity record suggests a possiblity for computation of sediment loads by computer. Instrumentation now in use for recording water quality parameters on digital punch tape could be used to record the output from a turbidimeter. Then, for streams having a good correlation between suspended sediment concentration and turbidity, simultaneous water discharge and turbidity data could be used to determine sediment loads by computer.     

Application of piezoelectric transducers in simulated rainfall erosivity assessment

Abstract

Rainfall simulators have often been used to mimic natural rainfall for studies of various land-surface and water interaction processes. The characteristics of the simulated rainfall are the main indicators used to judge the performance of the rainfall simulators. The aim of this study is to investigate the potential of piezoelectric transducers for measuring and evaluating a dripper-type simulated rainfall drop-size distribution (DSD) and kinetic energy (KE). The directly measured KE was significantly correlated with the estimated KE using the drop-size distribution and empirical rain drop fall velocity relationships. This result emphasizes the potential use of the piezoelectric sensor to directly measure and evaluate rainfall kinetic energy. Also, the relationship between rainfall intensity and KE showed good patterns of agreement between simulated rainfall and natural rainfall.

Citation Abd Elbasit, M. A. M., Yasuda, H. & Salmi, A. (2011) Application of piezoelectric transducers in simulated rainfall erosivity assessment. Hydrol. Sci. J. 56(1), 187–194.     

Towards environmental management of water turbidity within open coastal waters of the Great Barrier Reef

Water turbidity and suspended sediment concentration (SSC) are commonly used as part of marine monitoring and water quality plans. Current management plans utilise threshold SSC values derived from mean-annual turbidity concentrations. Little published work documents typical ranges of turbidity for reefs within open coastal waters. Here, time-series turbidity measurements from 61 sites in the Great Barrier Reef (GBR) and Moreton Bay, Australia, are presented as turbidity exceedance curves and derivatives. This contributes to the understanding of turbidity and SSC in the context of environmental management in open-coastal reef environments. Exceedance results indicate strong spatial and temporal variability in water turbidity across inter/intraregional scales. The highest turbidity across 61 sites, at 50% exceedance (T₅₀) is 15.3 NTU and at 90% exceedance (T₉₀) 4.1 NTU. Mean/median turbidity comparisons show strong differences between the two, consistent with a strongly skewed turbidity regime. Results may contribute towards promoting refinement of water quality management protocols.     

A reappraisal of the Engelund bed load equation

Abstract

Many bed load transport equations have been developed from differing standpoints. The Engelund equation has been selected for scrutiny since, although it accords well with experimental data in general, it has limitations under conditions of high bed load transport rates. The application of two phase flow theory has been used to derive an alternative “Engelund” equation which may be applied to both high and low transport rates.     

The manufacture of a three-dimensional transducer used in laboratory

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A NOTE ON INEXPENSIVE TELEMETRY OF RIVER SEDIMENT CONCENTRATIONS

Synopsis

An inexpensive method for continuous monitoring of suspended sediment concentrations in rivers has recently been developed at the University of Natal. The instrument uses newly available solid state electronic circuitry and has been thoroughly laboratory-tested. The circuitry and the operation of the instrument are described in general terms.     

Optimization of groundwater abstraction from a coastal aquifer

ABSTRACT

An analytical mathematical model, based on Jacobian elliptic functions, has been used to identify feasible wellfield locations and pumping rates for large-scale abstraction from an unconfined coastal aquifer. The choice of optimum feasible wellfield strategy has been made using a simple economic model which calculates the cost of the pipelines required to transport the abstracted groundwater to a large coastal city which forms the demand centre. Results indicate that the cheapest wellfield design would be a single large wellfield. However, because of the need to maintain at least a minimum supply in the city until a new surface water source is developed, a better solution may well be to develop two smaller wellfields pumping a greater total abstraction.     

Satellite remote sensing of water turbidity / Sonde de télémesure par satellite de la turbidité de l'eau

Abstract

Remote sensing instruments obtain an optical measure of water colour and turbidity. Colour increases the absorption of light in water and decreases the remotely sensed signal; turbidity increases the backscatter of light. For low concentrations of suspended materials, spectral reflectance is determined mostly by the absorptance characteristics of water; for higher concentrations, the absorptance characteristics of suspended particles are the most important factor. Remote sensing offers considerable advantages for the study of large areas, determination of current and circulation patterns, and monitoring of sedimentation, water productivity, and eutrophication.     

A STUDY OF RAINFALLS RECORDED AT THE CHERRAPUNJI OBSERVATORY

ABSTRACT

The maximum rainfalls recorded at the Cherrapunji Observatory raingauge during various periods within the 57 years from 1903 to 1959 have been studied and the equation of the enveloping line has found to be R = 49 D^0.485 where R is the rainfall in inches and D is duration in days. One-day maximum rainfalls for different periods from two to 100 years have also been worked out and the 100-year value has been found to be 2.1 times the 2-year value. The daily probable maximum precipitation (PMP), estimated by the Hershfield technique, is 78 in. A study of annual and monsoon rainfalls did not show any general linear trend but there was a gradual increase in amounts from 1944 to 1954.     

Seasonal description of the quality and quantity of snowmelt in a mountainous region using an integrated model

Abstract

An integrated model for the simulation and prediction of both snowmelt quantity and quality from seasonal snow cover in a mountain basin has been developed at the Institute of Hydrology and Hydraulics SAS in cooperation with the Geological Institute of Dionyz ?tur. The model will be used for both the simulation and forecast of snow accumulation and the accumulation of SO^2- ₄ washout. At the present time it is mostly used for simulation of the SO^2- ₄ concentration and water supply in snow. In this paper the results of SO^2- ₄ modelling in a brook are also presented.     

Book review

Abstract

This paper, which is partly drawn from the thesis work of one of the authors, presents experimental results of remote-sensing of plumes by optical radar.

Plume-rise theories from single stack emissions, due to Briggs (1969) and Moore (1974), were tested at different sites. Furthermore, a model for the rise of plumes will be described based on multiple sources of different heights and buoyancy fluxes. Finally, the fine structure of the plume cross-sections, deduced from the analysis of LIDAR echoes in terms of opacity (turbidity) ratios, will be shown     

Seasonal and inter-annual variability of water quality in the Uruguay River,Argentina

Abstract

Water quality of the Uruguay River was evaluated with multi-parametric (temperature, turbidity, conductivity, pH, dissolved oxygen) and sediment trap data (particle flux, total organic carbon and nitrogen contents) and correlated to precipitation, river discharge and El Niño Southern Oscillation (ENSO) indices for the period 2006–2011. Hydro-meteorological parameters averaged 24–85% variability with coincident precipitation (200–400 mm month^-1), discharge (7000–28 000 m³ s^-1) and turbidity peaks (50–80 NTU) in the austral spring, and absolute maxima during the El Niño 2009 episode. Spectral analysis of discharge and sea-surface temperature anomaly (SSTA) showed consistent variance maxima at approx. 3 and 1.5 years. Deseasonalized discharge was significantly correlated to SSTA. During river floods, pH decreased (from 7.5 to 6.6) and particle dynamics peaked (turbidity: 15–80 NTU; vertical fluxes: 20–200 g m^-2 d^-1; total solid load: <1000 to 100 000 t d^-1),whereas TOC remained stable (3.2 ± 0.8%) and C/N ratios increased (10–12) due to the higher contribution of terrestrial detritus.     

Development of a real-time forecasting model for turbidity current arrival time to improve reservoir desilting operation

ABSTRACT

Among various strategies for sediment reduction, venting turbidity currents through dam outlets can be an efficient way to reduce suspended sediment deposition. The accuracy of turbidity current arrival time forecasts is crucial for the operation of reservoir desiltation. A turbidity current arrival time (TCAT) model is proposed. A multi-objective genetic algorithm (MOGA), a support vector machine (SVM) and a two-stage forecasting technique are integrated to obtain more effective long lead-time forecasts of inflow discharge and inflow sediment concentration. The multi-objective genetic algorithm (MOGA) is applied for determining the optimal inputs of the forecasting model, support vector machine (SVM). The two-stage forecasting technique is implemented by adding the forecasted values to candidate inputs for improving the long lead-time forecasting. Then, the turbidity current arrival time from the inflow boundary to the reservoir outlet is calculated. To demonstrate the effectiveness of the TCAT model, it is applied to Shihmen Reservoir in northern Taiwan. The results confirm that the TCAT model forecasts are in good agreement with the observed data. The proposed TCAT model can provide useful information for reservoir sedimentation management during desilting operations.     

Hydromagnetic dynamo model with spiral convection

Summary The present paper deals with a hydromagnetic dynamo model of the generation mechanism of the Earth's magnetic field. An attempt has been made at selecting a flow-velocity field in the Earth's core which would satisfy the condition 0 for regenerating the field according to [2], and which would yield a velocity field pattern on the core surface as given in the papers by Kahle et al. [9]. These conditions are satisfied by the velocityv=V ₁+U ₂ ^c –V ₂ ^c and, geometrically, this velocity field is represented in space by a spiral convective motion. On the core surface two downflows and two upflows with the corresponding rotating cells may then be found. Only the axisymmetric harmonic component regeneration of the magnetic field has been considered. Adequate regeneration equations have been obtained by means of Braginski's method of quantity estimates in order of magnitude.     

Neural network model for discharge and water-level prediction for Ramganga River catchment of Ganga Basin,India

ABSTRACT

Discharges and water levels are essential components of river hydrodynamics. In unreachable terrains and ungauged locations, it is quite difficult to measure these parameters due to rugged topography. In the present study an artificial neural network model has been developed for the Ramganga River catchment of the Ganga Basin. The modelled network is trained, validated and tested using daily water flow and level data pertaining to 4 years (2010–2013). The network has been optimized using an enumeration technique and a network topology of 4-10-2 with a learning rate set at 0.06, which was found optimum for predicting discharge and water-level values for the considered river. The mean square error values obtained for discharge and water level for the tested data were found to be 0.046 and 0.012, respectively. Thus, monsoon flow patterns can be estimated with an accuracy of about 93.42%.

Editor M.C. Acreman; Associate editor E. Gargouri     

Turbidity and mass concentration of suspended matter in lake water: A comparison of two calibration methods

Turbidity measurements by foreward scattering nephelometer have been regularly conducted on the north basin of Lake Lugano (Switzerland/Italy) since September 1992. In order to determine mass concentrations from these data, both, in-situ and laboratory calibration experiments have been performed in November and December 1992 on suspended matter of the hypolimnion. Results show:

1. Mass concentration/turbidity ratios are different in the two turbidity zones examined due to variation in the optical signature of the suspended matter.
2. Laboratory calibrations using suspended matter originating from the water depths of interest give representative results provided that physical and chemical alterations occuring during the particle transfer process remain negligible.

     

Estimating suspended sediment concentrations from turbidity measurements and the calibration problem

In situ turbidity meters are being increasingly used to generate continuous records of suspended sediment concentration in rivers. However, the usefulness of the information obtained depends heavily on the existence of a close relationship between fluctuations in suspended sediment concentration and turbidity and the calibration procedure that relates suspended sediment concentration to the turbidity meter's signal. This study assesses the relationship between suspended sediment concentration and turbidity for a small (1·19 km²) rural catchment in southern Brazil and evaluates two calibration methods by comparing the estimates of suspended sediment concentration obtained from the calibrated turbidity readings with direct measurements obtained using a USDH 48 suspended sediment sampler. With the first calibration method, the calibration relationship is derived by relating the turbidity readings to simultaneous measurements of concentration obtained from suspended sediment samples collected from the vicinity of the turbidity probe during flood events. With the second method, the calibration is based on the readings obtained from the turbidity meter when the probe immersed in samples of known concentration prepared using soils collected from the catchment. Overall, there was a close link between fluctuations in suspended sediment concentration and turbidity in the stream at the outlet of the catchment, and the estimates of sediment concentration obtained using the first calibration method corresponded closely with the conventionally measured sediment concentrations. However, use of the second calibration method introduced appreciable errors. When the estimated sediment concentrations were compared with the measured values, the mean errors were ± 122 mg l^?1 and + 601 mg l^?1 for the first and second calibration procedures respectively. Copyright © 2007 John Wiley & Sons, Ltd.     

Convection in a rotating,laterally heated annulus pattern velocities and amplitude oscillations

Abstract

The velocities of the wave patterns relative to the rotating annulus have been measured with either increasing or decreasing positive radial temperature gradients and different rotation rates, with the fluid in thermal equilibrium and in contact with a rigid lid. The pattern velocities are dependent on initial conditions except in the unique areas of the stability diagram, where the velocities observed with either increasing or decreasing ΔT, overlap. The pattern velocities change discontinuously with each wave number transition, with a particularly large discontinuity at the transition from two to one wave. The frequency of the amplitude oscillations of the waves has been measured also. It has been found that the period of the oscillation of the three wave pattern is inversely proportional to the period of the pattern velocity, which means that in this case the ratio of the frequency of amplitude oscillation and the frequency of the pattern revolution is incommensurate.