Abstract Accumulations of snow behind fences may increase the water yield in windswept areas. The efficiency of snow collection depends on the reduction in wind speed in the lee of the fence. Wind speeds have been measured to windward and to leeward of vertical slat fences from 6 to 16 ft. high. The down-wind measurements were made at distances of 2.5H, 5H and 10H from the fence where H is the height of the fence. Speed measurements at various levels were integrated up to the height of the fence and the percentage reduction in wind speed was calculated. Expressions are given for the velocity reduction factor at distances down-wind of fences having a bottom gap, and for the cross-sectional area of a fully developed drift.

Abstract There is no universally acceptable technique available to estimate the magnitude and frequency of floods. The “rational method”, empirical formulae and regional analysis all have restrictions. The remaining approaches are deterministic, using design precipitation maxima and probabilistic, the latter using streamflow data to calculate frequencies. The concepts of design maxima and the fitting of statistical distributions to flood frequencies are discussed in detail. It is concluded that a more logical cost/benefit approach is required to decision making in spillway design.

Summary A test is presented to reveal automatically doubtful water levels and to detect sudden or gradual modifications of the stream flow. Each hydrometric station in a catchment area, homogeneous as to climatic conditions, is compared with a reference station. For this purpose we consider the ratios of the daily “reduced” water levels of the station under examination to the corresponding levels of the reference station. The “reduction” of the daily water stages is achieved by a fictitious shifting of the scale so that the mean yearly water level is placed at a predetermined level (the same everywhere) and by a dilatation (or a shrinking) of this scale so that the range Δ (the difference between the largest and the smallest monthly water levels) is equal to the range Δ0 of the reference station. The daily ratios of the reduced water levels are consequently approximately 1 either with high or low water. When a daily ratio deviates too much (more than 10 % for instance) from the mean monthly ratio, the corresponding water level is considered as doubtful and must be verified. If the running mean monthly ratios do not remain approximately uniform but change suddenly or slowly, it is because the stream flow is disturbed and the reason for this disturbance must be investigated. The test, used in a converse way, can also be satisfactorily used for filling in gaps in the observational data. Some examples enable the value of the method to be assessed.

(1971). REPORT ON PRECIPITATION. International Association of Scientific Hydrology. Bulletin: Vol. 16, No. 4, pp. 37-47.

Abstract In statistical hydrology, three different methods have been used to calculate the expected values of observable quantities in an ensemble. The first is to use an observable as a parameter to characterize the “states” of the ensemble and then to calculate the average value of the observable over all possible states; this is the expected value. The second method is to use an observable as a parameter to characterize the “states” and then to designate the most probable value of the observable as the expected value; this is known as the “minimum variance principle”. Finally, the third method is to use a parameter different from an observable to characterize the “states” and then to take the value of the observable for the most probable state as the expected value. Of all these different methods, only the first one is, in principle, physically correct. Thus, a study was made to determine the situations where methods other than the first can be used to calculate the expectation values of observables. I...

Abstract Water-borne, fluorescent tracers are conventionally detected by fluorometrically analysing liquid samples taken discretely or continuously from the water body under test. A continuous, automatic, film system described here detects tracer concentrations of one part per billion (1 in 109), provides a time distribution of concentration changes, and combines low cost with ready portability. Field installations are self-operative for up to ten days. A single laboratory-based fluorometer can easily analyse the concurrent data input from fifteen or more field installations. Data can also be stored prior to fluorometry. Fluorescent tracers have been detected successfully by the film system under experimental conditions to gauge streamflow, to produce flow hydrographs, and to determine the travel time of streamflow. Further refinements should be made by potential users to optimize the system for specific needs.

Abstract The chemical composition of formation waters tapped in oil wells and emerging as hot springs along the Suez coast of Sinai was examined. A scheme is proposed for the geochemical evolution of these waters and their relation to the geological history of the area. The thermal regime in the investigated area is characterized by high gradient foci located in the immediate proximity of major faults. Fe—mineralization, dolomitization and concentrations of heavy metals were observed on the eastern shore of the Gulf of Suez. The Suez formation waters have equivalent ionic ratios similar to those of the hot brines found in the three Deeps of the Red Sea (Degens and Ross, 1969). The thermal and mineralization phenomena also show a resemblance to those of the Deeps.

Abstract The study is based on the 121 answers to the international survey on ground water recharge published in I.A.S.H. bulletin n° 87. After generalities about the aims, benefits, type of devices, recharged aquifers and size of plants, are examined: —The infiltration devices (basins canals). —The injection devices (wells). —The economical aspects of realisations. Diverse statistical correlations are found, and regression formulas proposed, concerning: —Connections between permeability, size of devices, and the injection or infiltration rate. —Connection between the annual input and the capital invested. The synthesis of these datas conduct to results which may be useful to pepare new-projects of artificial recharge.

Abstract A lot of different distribution functions have been proposed to represent the precipitation totals collected in k days, and in particular a transformed incomplete gamma distribution aimed to be the basis of the searched law (Formula 3.). This distribution contains as particular cases, or as limit-cases the distributions usually employed for the daily, weekly, monthly and annual precipitations. Periods even shorter than a day, as well as the intensity may be presented by the same law. The general validity of the proposed law is confirmed by applying it at the rainfall data coliected at the Observatory of Ghent.

SUMMARY In case of natural watercourses a permanent, gradually varying flow occurs only very rarely. Moreover at those wa*** courses where bed-load has a role, nearly always non-steady flow is the case. Any change in the flow evidently affects the dist*** covered by one step and the lengths of the rest periods between the single steps. For this reason no restriction has been m*** in the model for the density functions characteristic of the distribution of step lengths of a studied particle as of random *** ables, that is the step lengths are independent of each other and they represent a random variable having not necessarily only type of density function. As it is well-known, Einstein (2) supposed the distances covered by one step to be equal; while Hul and Sayre (15) applied in their model as starting condition the approach that the step lengths of the bed-load are of exponer*** distribution. To take into account the rest periods caused real difficulties at establishing the model. According to the perio...