River Depth Research Articles

Stable width and depth of straight gravel rivers with heterogeneous bed materials

Mathematical model for defining stable width and depth of straight gravel rivers is presented, in which it is revealed that the major agency for maintaining stable channel is lateral diffusion of longitudinal fluid momentum due to turbulence. The primary quantities which determine the stable channel geometry are found to be flow discharge, longitudinal free surface slope, the median size of bed material, and gradation of the bed material. Increasing gradation is found to increase the depth and decrease the width. Introduction of one loose and the other rigid bank in laboratory experiments provides good examples to test the model, in which four kinds of sand were used to test the gradation effect. These laboratory data support the mathematical model presented herein. The theory also performs well when it is applied to natural gravel rivers.

Paleohydraulic reconstruction of a late cretaceous river in the middle Benue trough (Nigeria) and its limitations

Several fining-upward cycles and epsilon cross-bedded units have been recognized in the fluvial Makurdi Formation (Turonian) of the Benue trough of Nigeria. The maximum thickness of a coarse-member unit of a fining-upward cycle served as a measure of the bankfull depth ( D) of the ancient Makurdi river. The width ( W) of the river has been estimated from Cotter's regression equation which related width of a stream to its depth. After determining percentages of silt-clay content in channel bed ( Sc) and channel bank ( Sb), the basic data have been used in several empirical equations and graphs derived by Schumm and others to estimate morphology and flow characteristics of the Makurdi river. The results indicate that the ancient river in the study area was about 227 m wide and 10 m deep; it had a 900 km long, meandering channel; the meander wave length averaged 2580 m with an amplitude of about 1186 m and a mean radius of curvature of about 640 m. The river drained an area of about 57 000 km 2; it had a mean annual discharge of about 640 m 3 sec −1 and a mean annual flood of 2300 m 3 sec −1; the discharge at bankfull stage was 2300–2600 m 3 sec −1. It was a mixed-load river with a bankfull flow velocity of 219 cm sec −1 and a moderate gradient of about 0.14 m km −1. There are several limitations in the paleohydraulic methodology. The most serious of these is the likelihood of getting widely divergent results from using several of the empirical equations. The majority of the existing empirical relations and graphs have been derived from studies of stable channels in temperate regions; their validity for larger rivers in tropical setting, which have great preservation potential in the rock record, has not been tested. The results may also suffer from use of only a few measured variables to calculate other variables and parameters of a paleochannel so that errors are compounded. Nevertheless paleohydraulic measures provide an approximation of the morphology and flow characteristics of an ancient channel.

Tests of frazil collector lines to assist ice cover formation

A preliminary investigation was made of the effect of frazil ice on arrays of lines positioned in flowing water under winter conditions. It was found that the lines would provide a stable basis for forming an ice cover on many stream reaches that would normally remain open because of high velocity and shallow depths.Tests were conducted in a refrigerated flume and in small mountain rivers. Flume depths varied from 2 – 22 cm and river depths varied from 33–50 cm. Average flow velocities had a range of 0.08–0.84 m/s in the flume and a range of 0.6–0.8 m/s in the rivers. Frazil ice would grow on a line quite rapidly achieving a diameter of 32 mm in 15 min, on a 3.2 mm dia, line in the flume. In the river, overnight accumulations reached 20 cm in depth. A few drag force measurements were made which yielded an average shear drag coefficient of 0.16.The results suggest methods of increasing our control over ice.

Application of underwater light measurements in nutrient and production studies in shallow rivers

SummaryDue to fluctuations in water turbidity, river depth and total reflection from one river section to another, plant production is poorly correlated to solar radiation incident on the water surface. A relationship was observed between daily relative photosynthesis and photosynthetically available radiation (PAR) at the plant depth for Cladophora, with a correlation coefficient (r) of 0·73. Therefore, the effect of low light levels can be compensated for when evaluating nutrient‐growth relationships for Cladophora in the field.

Observations on sampling pre-imaginal populations of blackflies (Dipt., Simu liidae) in West Cameroon

The use of standardised artificial substratum units (SASUs) for sampling preimaginal populations of Simulium is reviewed and the results then given of experiments with SASUs in rivers and artificial streams in West Cameroon in 1968–70. The increase of downstream drift of larvae by night is attributed to the increased activity of associated fauna at night. The numbers of larvae settling on SASUs is partly afunction of how long the latter have been set and partly due to the pattern of fluctuation in river depth. Any particular SASU appears to be selective in relation to the different species of Simulium available for settlement. A new index of uniformity is proposed for comparing the diversity of Simulium faunas occurring on different substrata.

Numerical Solution of Flow Problems in Rivers

Calculation of future river depths and velocities using differential equations of physical laws governing such flows; computer calculations with new methods for numerical analysis of three cases; floods of 1955 on 375 mi stretch of Ohio River, flood of 1947 at junction of Ohio and Mississippi, and flood of 1950 through Kentucky reservoir.

THE SALT WEDGE

The "salt wedge" is an idealized model of a phenomenon encountered in some estuaries. It consists of a layer of fresh river water flowing over and past an underlying layer of heavier salt water. The following study is an attempt to predict the shape of the salt wedge and its length measured from some significant point in the estuary in terms of quantities, such as the densities of the fresh and salt water, the average river depth and velocity, etc., which are usually available.

On the Meandering

The meandering is considered morphometrically on some rivers in Hokkaido. Fig. 2A shows the inclination and the river width of free meandcr, which stand in the relation of hyperbola as Prof. G. Imamura said on the inclination and the width of meanderbelt. In Fig. 2A the depth of river is not considered, but as the depth increases, the inclination of river becomes gentle. Figt. 2B and 2C represent the meanderindex:Stream-distance-Axial-distance/Axial-distance×100and the wavelength of meander. (Distance ac in Fig. 1). According to Fig. 2C we find that the river winds with a certain wavelngth and the width of meanderbelt is nearly half of the wavelength.