Name:______
Stream Channels
MEASURING STREAM VELOCITY AND CALCULATING DISCHARGE
The discharge of a stream is its volume of flow per unit time (e.g. m3/s).
In equation form, the discharge is determined by multiplying the cross-sectional area of
the stream by the stream velocity:
Discharge = Cross sectional area (m2) x Velocity (m/s)
The cross sectional area is determined by measuring the stream width and depth, so
That
Cross sectional area =Stream width (m)x Stream depth (m)
Only in this case, everything has been scaled down to the cm scale. You will now calculate discharges and cross-sectional areas for three different stages within the stream channel, as one would at a stream gauging station. For each of the three stream levels, drop a bead into the straight channel, just upstream of the attached ruler for each level, and using a stop watch, record the time it takes for the bead to travelthe whole length of the ruler. You will also have to measure the width of the three stream channels. Record your observations below and complete the following calculations:
1) Narrowest channel (depth = 0.25cm)
Velocity______(cm/s) = Distance 45 (cm) / Time ______(sec)
Cross sectional area(1)______(cm2) = Width______(cm) x Depth .25 (cm)
Discharge______(cm3/s) = Cross-section area______(cm2) x Velocity______(cm/s)
2) Middle channel (depth = 0.5cm)
Velocity______(cm/s) = Distance 45 (cm) / Time ______(sec)
Cross sectional area(2)______(cm2) = (Width______(cm) x Depth .25 (cm)) +
Cross sectional area (1)______(cm2)
Discharge______(cm3/s) = Cross-section area______(cm2) x Velocity______(cm/s)
3.) Widest channel (depth = 0.75cm)
Velocity______(cm/s) = Distance 45 (cm) / Time ______(sec)
Cross sectional area(3)______(cm2) = (Width______(cm) x Depth .25 (cm)) +
Cross sectional area (2) ______(cm2)
Discharge______(cm3/s) = Cross-section area______(cm2) x Velocity______(cm/s)
Creating a Stream Gauging Station
On the graph below, plot three points for the three stream channel depths, discharge (y-axis) v. depth (x-axis), connecting the three points with a smooth curve. This curve illustrates how discharge increases with depth.
Stream Channel Meanders
1.) Drop a bead along the outer-bank of the large meander (where the first red arrow points), using the stop watch, record the length of time it takes for the pellet to travel from the first to the last red arrows, and record below. Divide the number of cm by the number of seconds. This is the velocity in cm/s. Repeat for the inner bank (blue arrows) and record your results below.
Inner bank
Distance 20 (cm) / Time______(sec) = Velocity______(cm/s)
Outer bank
Distance 25 (cm) / Time______(sec) = Velocity______(cm/s)
2.)Insert a small amount of sand into the top of the stream before the first meander with the stream running at a moderate velocity. Where does all the sand deposit along the meanders? Sketch in the area within the stream channel on Fig. A , where the sediment deposited.
3.)Remove the small section of stream bank, cutting out the main meander redirecting the higher velocity current; add a little more sand up stream of this point. What landform is created? Again, sketch in the area within the stream channel on Fig. B, where the sediment deposited.
DAMS AND FLOODS
1)Insert the dam at the end of the meander belt/top of the straight section. Let the reservoir behind the dam fill up with water. The water will spill over the top of the dam when it is full. Now dribble some sand into the reservoir behind the dam. You have just demonstrated how siltation works. What happened?
______
2)To see how flooding affects communities, place some houses along the banks of the straight section of the stream. Now flip out the dam and allow the water to flood the straight section. This simulates a damburst. What happens to the houses?
______
What happens to the sediments in the bottom of the reservoir and why?
______