It was found that in low-transport, flat-bed flows, where particle transport occurs by rolling and sliding along the bed, from 15°c to 20°c. In high-transport, flat-bed streams with suspended sediment transport, it was observed that the effects of temperature on bed load discharge are qualitatively the same as those obtained at low levels. 6 Effect of water temperature on sediment discharge and mean shear stress in a low-velocity sediment transport flow over a flat bed.
Data from low-transport, flat-bed experiments with well-sorted, naturally-worn silica in which the bed-loading-discharging hypothesis was tested.
CHAPTER 1 INTRODUCTION
The aim of this study was to investigate the mechanisms by which temperature can influence sediment discharge and boundary roughness. Chapter 2 provides a brief overview of the reported temperature effects on sediment discharge, bottom configuration and roughness; and of Rouse's suspended distribution theory and Einstein's bed load function, into which explicit attempts have been made to integrate this. Chapter 6 further discusses the experimental results and puts forward a phenomenological explanation for the observed temperature effects on sediment discharge in low-transport flat-bottom currents.
In the last part of the chapter, an attempt is made to connect the results obtained in this study with the effects of temperature that have been observed in natural streams.
CHAPTER 2
In the ripple pair, when the water temperature was increased to 36 °C, the measured sediment discharge decreased by 64% and the calculated Darcy-Weisbach friction factor of the bottom decreased by 22%. With these relations the temperature effect on the soil load of particles with different sizes can be calculated. The unloading function of the bed is plotted in figure and U~b = JT~b/p, where T~b is the shear stress of the bed due to grain roughness.
2. 8) a change in water temperature can affect the bed discharge of uniform bed materials by affecting the viscous shielding of the bed particles and the average lift rate.
CHAPTER 3
There are four 1000 watt immersion heaters located in the return pipe near the upstream end. In the lower reach, glass observation windows, 58 inches high, were placed in each wall of the flume. Using a point measuring device and a still water surface in the channel, the differences in the carriage rails and the bottom of the channel and the calibration of the inclined rock were checked.
To sample the sediment discharge, a tube was suspended vertically in the throat of the outlet box.
PLASTIC TUBING
TUBE SUPPORT COLLAR
IMPELLER
TO SAMPLER COLLECTION
SEDIMENT DISCHARGE
The sampling platform can be raised or lowered to create the height difference necessary to match the sampling rate to the average velocity in the exhaust throat. The sampling rate was determined based on the flow rate in the sampler, which was obtained by measuring the volume of the sample and the time to collect it. The Pitot tube was connected to an air-water vertical differential manometer that could be read to the nearest zero.
3/16 in. BRASS TUBE
CHAPTER 4
Except in Series G, the bed material was the same for all the experiments in a series. In experiment G-4, the maximum difference in water temperature from one side of the flume to the other was 0. The maximum temperature difference along the flume in each of the other experiments was less than 0.
At the upstream end of the river the bed was contoured to provide a gradual change in flow depth from approximately 12 cm at the inlet to 6. The slope of the water surface relative to the river was determined by placing a straight line on the Profile of water surface taken from gauge readings at various stations along the survey stretch. While in the fine sand experiments of Series B, the bed heights were obtained by direct measurements, in Series C they were calculated using the heights measured near the tops of the bed particles.
In Series D, the experimental procedure was similar to that used in Series C, but the nature of the bed material necessitated the following modifications. A fixed bed section was used at the upstream end of the channel to create a boundary layer and prevent scour downstream of the inlet. Three 8,460-watt electric heaters installed in the return pipe of the 60-ft channel were used to maintain water temperature during the E-series experiments.
To maintain the water temperatures required in the Series G experiments, four 1000-watt heaters and two 8460-watt heaters were used in the return line of the 40-foot chute. In these experiments, sediment discharge samples were collected at the beginning of the return pipe using the sampling tube described in Section 3.
CHAPTER 5
However, in each case the mean bed shear stress was lower in the warm water flow. Thus, it was the 30% increase in R*b that produced the several-fold increase in sediment discharge in the warm water stream of each pair of experiments in Series B. These effects of temperature on bed load discharge are qualitatively the same as those observed in the Series B experiments where the limiting Reynolds numbers.
In both cases, sediment discharge from warm water was greater, even though the concentration gradient of warm water was greater than that in the cold water stream. This suggests that for each of these size fractions, bottom discharge was greater in the warm water stream. The limiting Reynolds numbers of the two coarsest fractions in experiments F-27 and F-28 exceeded 18 (see Table 5.5), and the relatively small sediment discharge ratios Q. 52 suggest that the bed load discharge of these two size fractions in the cold water stream was actually larger .
So the larger bedload concentration and discharge in the warm water experiment of this pair is also consistent with the low. These results indicate that the qualitative temperature effects on bedload discharge observed in the Series B flatbed experiments can also occur in flows where the bed configuration is not flat. In each case, a least squares fit to the data was used to remove the nonzero linear trend in the bed profiles.
26 examples of spectral variations present in sets of ripple and dune profiles are provided; and in Fig. In pairs of experiments where the bedform consisted of ripples in both cold and warm water, the variations between the spectra flow. In pairs of higher velocity experiments, the differences between the mean spectral estimates of cold and warm water (Fig. 5.
3, the bed ripples formed by the warm water flow (F-10) were noticeably longer than those in the cold water flow.
CHAPTER 6
1 show that at limiting Reynolds numbers smaller than values close to 36 (y* < 10), with an increase in water temperature, there is an increase in the intensity of turbulence near the tops of the bed particles. But for R*b values greater than 36, Ju decreases with increasing temperature. The increase in sediment discharge with increasing water temperature in experimental pairs of series B (R.,'
In series .H and C where the values of R*b were larger, the decrease in sediment discharge with increase in water temperature can correspond to decrease in Ju·a according to Figure 1. This also indicates that the relative change in Ju18 with increase of the water temperature. the water temperature is greater for values of u*by/\I less than 36 than for higher values. Data from experiment pair F-23 and F-24 where the bottom was flat indicate that the bottom loading was greater in the warm water flow.
1 for this range of limiting Reynolds numbers with an increase in water temperature there will be an increase in bed load discharge. These experimental results (F-33, F-34, G-8 and G-9) show that in streams where the values of R~b are small, with an increase in water temperature and consequently a possible increase in the load of the bed. discharge, the development of the bed with warm water causes in a cold water to flow at the same discharge and depth. Thus in the F-25e and F-26e the bed load discharge was probably greater in the warm water experiment.
These data suggest that for a given velocity and depth, an increase in bottom load discharge with an increase in water temperature does not necessarily indicate that it is as warm. In both cases, dune-like bottom waves were observed in the warm water flow, but at lower water temperature the bottom shape became flat.
CHAPTER 7
- APPARATUS
- SEPARATION PROCEDURE
With wave bed currents over fine sand, the hydraulic roughness of the bottom with warm water is smaller than with a cold water flow at the same discharge and depth. The drained sand sank to the bottom of the container and the water overflowed into a nearby drain. The characteristics of the eight size fractions obtained from the fall velocity separation are given in Table B.
The increase in sediment discharge outlined in result one can be partly explained in terms of the temperature effect on the particle fall velocity, w. This "roughening" is believed to be caused by a change in the character of the bed configuration with temperature. The fact that in this case the slope and friction factor decrease as temperature and velocity increase is a manifestation of the temperature effect on the friction factor by changing the bed shape.
The qualitative results of the CIT study are basically in agreement with the corresponding results obtained from the authors' data. This is due to the intersection of the contours of constant temperature near the entry into region 3 and the reversal in slope. In several natural streams (1, 14), it has been found that for a given flow, a drop in water temperature causes an increase in the mean flow velocity and sediment discharge, especially for that part of the load in the size of fine sand ( 0.05 mm ~ d8 ~ 0.35 mm ), with a consequent reduction in the friction factor.
Based on the author's technique (least-squares fitting) for calculating these slopes, the differences indicate that non-uniform flow (return water profile) existed for at least part of the channel length. This unevenness of flow may explain some of the scatter in the author's rune of duplicating fine sand.
