DILUTION GAUGING ON THE RECESSION LIMB: 1. CONSTANT RATE INJECTION METHOD / Mesures par dilution sur la courbe de tarissement: 1. Méthode par injection de taux constant

Abstract

The application of dilution gauging techniques to rivers and streams and other variable flows incurs a systematic error caused by the change in discharge with time. The discharge calculated from dilution gauging results may be considered as an estimate of the stream discharge at the injection section or the sampling section, and the magnitude and sense of the error vary according to this choice.

On the recession limb of a hydrograph and in other cases where the discharge may be expected to change smoothly and gradually, the equations derived from the residence time model previously proposed by the author may be linearized, and formulae of general applicability developed.

In this paper formulae are presented for the error arising in the case of a constant rate tracer injection, and examples are given of their application to results from a number of different flow systems. It is shown that the error may be significant in two situations: where the rate of change of discharge is high and where poor mixing necessitates long gauging reaches and hence long tracer injections.     

THE EFFECT OF EVAPOTRANSPIRATION ON STREAMFLOW RECESSION / L'effet de l'évapotranspiration sur l'écoulement en décrue

Abstract

The effect that evapotranspiration has on recession curves during low flow periods is explored. Recession constants are obtained from flow data and plotted against the average daily pan evaporation occurring during the recession. The results for the three study basins are similar, showing a decrease in recession constant with an increase in average daily pan evaporation. For low values of average daily pan evaporation, the recession constant approaches a constant value.     

THE TWO-AXIS METHOD: A NEW METHOD TO CALCULATE AVERAGE PRECIPITATION OVER A BASIN / La deux-axes méthode: une nouvelle méthode pour la calculation de la précipitation moyenne d'un bassin versant

Abstract

The two-axis method, used to calculate average precipitation over a basin, is based on three assumptions inherent in the Thiessen and isohyetal methods. The method follows four steps: (1) The two axes of a basin are drawn following a standard procedure; (2) for each raingauge location a station angle is determined by either measuring or calculating the angle between lines connecting the station location to the farthest ends of the two axes; (3) each station is assigned a weight (the ratio of its angle to the sum of all station angles); (4) average area precipitation is calculated as the sum of the products of corresponding station weights and measured precipitation. The method is fast, efficient, and is readily computerized.     

A METHOD OF ESTIMATING THE PROBABILITY OF OCCURRENCE OF SNOW WATER EQUIVALENTS IN THE UNITED KINGDOM / Méthode pour l'évaluation de la probabilité de l'occurrence des équivalents neige-eau au Royaume Uni

Abstract

A simple guide (shown in the appendix) is produced, which enables a water manager or engineer to make an estimate of statistics of water equivalent of snow cover for return periods between 5 and 100 years for most places in the United Kingdom. This paper describes how the guide was produced using many different sources of data. The methods described here will be of help to both meteorologists and hydrologists in temperate countries with similar snow questions.     

Optimization of streamflow measurements by the dilution of the food colorant E110 / Optimisation de la mesure de débit par dilution du colorant alimentaire E110

Abstract

This study presents the measurement of streamflows by constant dilution of a yellow-orange food colorant (E110). Field measurements are carried out in the Doria River, a mountain torrent in the Savoie pre-Alps, France. A limnimetric station installed 12 years ago is periodically calibrated by mechanical and chemical measurements. Moreover, simultaneous mechanical and chemical methods allow the statistical validation of the proposed technique. The main advantages of this method are the lack of toxicity, the absence of visible river colouring, comparable to that of aquatic organic matter, and the low detection limit. This method allows high flow measurement under suitable conditions.     

Coding random self-similar river networks and calculating geometric distances: 2. Application to runoff simulations / Codage de réseaux hydrographiques auto-similaires aléatoires et calcul de distances géométriques: 2. Application à la simulation de l'écoulement

Abstract

A preliminary method for coding random self-similar river networks and the corresponding distance calculations are proposed in a companion paper. The coding method is applied to generate random self-similar river networks, and the corresponding algorithm for calculating the geometric distances of the links is employed to determine the width function of the river networks, and thus evaluates the adaptability of the process. The width function-based geomorphological instantaneous unit hydrograph (WF-GIUH) model is then applied to estimate the runoff of the Po-bridge watershed in northern Taiwan. The results imply that the separately random self-similar generating algorithm can be used to simulate river networks during the rainfall–runoff process. It can also help analyse the variations of the river network when rainfall locations change and study the influence on hydrological responses (IUH) when the shape of river network changes.     

Trend detection in river flow series: 2. Flood and low-flow index series / Détection de tendance dans des séries de débit fluvial: 2. Séries d'indices de crue et d'étiage

Abstract

Major floods in Europe and North America during the past decade have provoked the question of whether or not they are an effect of a changing climate. This study investigates changes in observational data, using up to 100-year-long daily mean river flow records at 21 stations worldwide. Trends in seven flood and low-flow index series are assessed using Mann-Kendall and linear regression methods. Emphasis was on the comparison of trends in these flow index series, particularly in peak-over-threshold (POT) series as opposed to annual maximum (AM) river flow series. There is a larger number of significant trends in the AM than in the POT flood magnitude series, probably relating to the way the series are constructed. Low flood peaks occurring at the beginning or end of a time series with trend may be too low to be selected for the POT analysis. However, one peak per year will always be selected for the AM series, making the slope steeper and/or the series longer, resulting in a more significant trend. There is no general pattern of increasing or decreasing numbers or magnitudes of floods, but there are significant increases in half of the low-flow series.     

Coding random self-similar river networks and calculating geometric distances: 1. General methodology / Codage de réseaux hydrographiques auto-similaires aléatoires et calcul de distances géométriques: 1. Méthodologie générale

Abstract

This study proposes a preliminary method for coding random self-similar river networks as a series of numbers, and investigates the corresponding algorithm that calculates the geometric distances from the code series. The coding method, generating random self-similar patterns with various probabilities of particular pattern links, and transferring the pattern into numerical code series, is proposed, based on the wide range of stochastic characteristics of natural patterns. The heredity of self-similarity and the connecting relationships inside the generated pattern are discussed. Finally, the algorithm to calculate the geometric distances of the generated pattern are developed.     

Reuse of waste water: impact on water supply planning / Remploi de l'eau résiduaire: influence sur la planification des systèmes de distribution des eaux

Abstract

As the urban population of the world increases and demand on easily developable water supplies are exceeded, cities have recourse to a range of management alternatives to balance municipal water supply and demand. These alternatives range from doing nothing to modifying either the supply or the demand variable in the supply-demand relationship. The reuse or recycling of urban waste water in many circumstances may be an economically attractive and effective management strategy for extending existing supplies of developed water, for providing additional water where no developable supplies exist and for meeting water quality effluent discharge standards. The relationship among municipal, industrial and agricultural water use and the treatment links which may be required to modify the quality of a municipal waste effluent for either recycling or reuse purposes is described. A procedure is described for analysing water reuse alternatives within a framework of regional water supply and waste water disposal planning and management.     

Estimation by photogrammetry of the glacier recession on the Cotopaxi Volcano (Ecuador) between 1956 and 1997 / Estimation par photogrammétrie de la récession glaciaire sur le Volcan Cotopaxi (Equateur) entre 1956 et 1997

Abstract

Aerial photographs of the Cotopaxi Volcano ice cap dating from 1956 to 1997 were used to quantify the evolution of the surface area. Results were obtained using precise stereoscopic methods that give the most accurate information. In addition four specific glacier tongues were investigated in detail to measure the ice mass lost between 1976 and 1997. Surprisingly, the bedrock morphology is shown to be very irregular and this explains a large extent of the variability found in the ice losses. The results show that glaciers stagnated from 1956 to 1976 and lost about 30% of their surface area between 1976 and 1997. Slope exposure did not seem to have any significant effect since all the glaciers of the volcano retreated in the same proportion. In accordance with specific measurements performed on the nearby Antizana 15 Glacier, it is suggested that the strong recession observed after 1976 was associated with increasing melting conditions which have occurred repeatedly during the intense/long-duration warm ENSO phases.     

Soil moisture estimation using ERS 2 SAR data: a case study in the Solani River catchment/Estimation de l’humidité du sol grâce à des données ERS-2 SAR: étude de cas dans le bassin de la rivière Solani

Abstract

Abstract The information regarding spatial and temporal variation of soil moisture in a catchment is of utmost importance in hydrological, as well as many other studies. Point measurements from gravimetric and other methods for soil moisture determination are insufficient to understand the spatial behaviour of soil moisture in a region. Microwave remote sensing data from active sensors on board various satellites are increasingly being used to map spatial distribution of soil moisture within the 0–10 cm top surface. The northern part of India has a network of large rivers and canals and, therefore, spatial and temporal distribution of soil moisture in this region has a significant bearing on the hydrology of the region. In this paper, results on estimation of soil moisture from an ERS-2 SAR image in the catchment of the Solani River (a tributary to the River Ganga) in and around the town of Roorkee, India, have been presented. The radar backscatter coefficient for each pixel of the image has been modelled from the digital numbers of the SAR image. Gravimetric measurements have been made simultaneously during the satellite pass to determine the concurrent value of volumetric soil moisture at a large number of sample points within the satellite sweep area. The backscatter coefficient is found to vary from –30 dB to –42 dB for a variation in soil moisture from 30 to 75%. Regression analyses between volumetric soil moisture and both the digital numbers and backscatter coefficients were performed. Strong correlations between volumetric soil moisture and digital number were observed with R ² values of 0.84, 0.75 and 0.83 for bare soil, vegetative and combined surfaces, respectively. A similar trend was observed with the relationship between backscatter and volumetric soil moisture with R ² values of 0.60, 0.89 and 0.67 for bare soil, vegetative and combined surfaces, respectively. These results demonstrate the utilization of SAR data for estimation of spatial distribution of soil moisture in the region of the present study.