Presentation

The targets of this activity are to delineate how channel properties influence the speed of stream in streams, and to show how varieties in tempest and waste bowl qualities influence release. Water streaming in a stream channel is pulled downslope by the power of gravity. Neutralizing this power is the drag or opposition that the channel presents to the stream. The association of these two powers (gravitational and opposing powers) decides the stream speed of water in the channel. The stream speed can be estimated straightforwardly utilizing a current meter, or assessed from the properties of the stream channel. One of the most widely recognized techniques for assessing stream speed is the Manning Equation.

Manning Equation:          V = R ^0.66 x S ^0.5

                                                      n                                                                

                 where:           V = stream flow velocity (m/s)

                                       R = hydraulic radius of the flow (see below)

                                       S = channel gradient (dimensionless rise/run)

                                       n = Manning’s roughness coefficient (see below)

In streams and waterways, the pressure driven range of the stream (R) is gotten by separating the cross sectional territory of the channel by the wetted edge of the channel. Keeping an eye on\'s unpleasantness coefficient (n) is an observational consistent, which communicates the opposition that the channel presents to water stream. The estimation of n increments as the harshness and anomaly of the channel builds (Table 1). The Manning Equation shows that stream speed will increment as stream profundity and channel inclination increment, and decline as the channel gets harsher.

            TABLE 1: Manning n for various channel types

Channel description	n
Clean, straight, no rapids or pools	0.035
Clean, winding, some pools and shoals	0.042
Sluggish reaches, weedy, deep pools	0.084
Very weedy, deep pools, encroaching shrubs	0.11

The rate that water courses through a cross-segment on a stream is acquired by increasing the cross-sectional region of the stream (A) by the speed of the stream (V). This stream rate, named the stream release (Q), is usually communicated in units of m3/s. The all out volume of water streaming past a traverse time can be determined by increasing the stream release by the length of the timespan.

1. Table 2 shows the change in the area (A) and hydraulic radius (R) of a stream cross-section during and after a storm. Complete the Table by using the Manning Equation to calculate the flow velocity and discharge of the stream at the observation times. For your calculations, assume that the stream channel is clean and winding with some rapids and shoals, and that it has a gradient of 5 m/km (S = 0.005). (24 marks)

TABLE 2: Observations of area and hydraulic radius on a hypothetical stream

Time (hrs)	A (m2)	R	V (m/sec)	Q (m3/sec)
midnight	71	0.33
12:15	71	0.33
12:30	193	0.52
12:45	287	0.81
1:00	348	1.33
1:15	301	0.92
1:30	252	0.82
1:45	203	0.46
2:00	169	0.43
2:15	119	0.41
2:30	92	0.25
2:45	83	0.35

Discharge varies over time, largely in response to variations in precipitation and snowmelt over the drainage basin that supplies water to the stream. A graph of the variation in stream discharge over time is termed a hydrograph. The part of the hydrograph that represents the increase in flow initiated by a storm is termed the rising limb, while that representing the decline in flow after the storm is termed the falling limb.

2.  Plot the stream discharge values calculated in Table 2 above as a hydrograph on Fig. 1. Label the rising limb, falling limb, and peak of your hydrograph. Determine the total volume (in litres) of water which flowed through the cross-section between midnight and 3:00 A.M. Assume that your calculated discharges (Q) apply for the full 15 min after the time at which they were calculated. (Hint: 1 m³ = ? litres). (13 marks)

Total Volume: