River Studies

Outline of Events During your river field work you will be visiting two different sites in the lower course of the river. At each site you will be taking measurements to find out the River width River depth Shape of the river channel Velocity of the river You will also be completing field sketches

Course of the river A river flows from its source in the mountain to its mouth, where it enters the sea. The route the river takes is referred to as its long profile. The long profile is divided into 3 sections Upper, middle and lower. Each section has unique features and behaviour

Upper valley characteristics

“ V”shape valley, vertical erosion dominant Interlocking spurs Slumping and landslides - very active hill slopes Narrow, shallow channel, low velocity and discharge Large bed load derived from upstream and from valley sides

River load in upper course Boulders are large and semi- rounded, due to attrition within the load and abrasion with the stream bed and banks Why are they rounded?

Waterfalls are also located in the upper course Plunge pool Waterfall creates gorge as it recedes upstream by eroding the base and neck HOW IS A GORGE FORMED?

Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom First signs of meanders River channel wider, deeper, greater velocity and discharge

Here we find meanders

Meander, R. Lavant, Chichester Floodplain Point bar deposits on the inner meander bend where there is low energy River Cliff Slip-Off Slope

Lower Course,Severn Valley Well developed meanders with bars in the channel indicating high sediment load Very gentle valley side gradients Very wide floodplain

Summary of valley characteristics

So how do we collect the data? First lets look at River Width & Depths Cross-Sections Then River speed

Equipment 2 x Ranging Poles Long stiff ruler Tape Measure (waterproof) Recording sheet How many People? (at least 3)

Stream Width Stretch the tape measure at 90° to the course of the river from one bank to the other Start & finish measuring where the bank meets the water. Pull the tape measure tight to prevent the flowing river from dragging the tape measure - a height of 20 to 30 cm above water.

Method LEFT BANK RIGHT BANK A stream channel with depth surveyed every 20cm

Measuring the depth

The thinnest edge of the ruler must face into the current The narrow edge of the ruler must face upstream to minimise the surface area facing the running water. This helps to prevent 2 problems: The formation of a bow wave The force of the water bending the ruler

Stream Depth River depth is measured at regular intervals across it's width. The number of readings taken depends upon the river width and how much detail is need for your cross-section. 50cm intervals (samples) are a compromise between excessive readings and loss of detail. Use the tape measure to help you take a straight line transect survey across the river. A stiff rigid ruler should be used to measure the depth of the river at 50cm intervals across the entire width of the river. Allow the ruler to touch the bed of the river. If the water becomes too deep for a meter rule, use a surveying pole with the depths marked on it.

Data LEFT BANK RIGHT BANK A stream channel with depth surveyed every 20cm

How to measure the Speed of a River

Equipment Stop watch 4x Ranging Poles Floats - What type of float? (oranges/tennis balls) Tape Measure

How to collect the data Put 2 ranging poles on opposite sides of the river to create a start line Measure out a 10 m distance downstream and place 2 more ranging poles to create a finishing line Release an orange into the river upstream (above) from the start line. Record the time it takes for the orange to travel the 10m distance from the start and finish.

Method LEFT BANK RIGHT BANK 10 m

Calculation of Speed Speed = Distance Time ___________________________________________ Units m/s (meters per second) Example 1 :A distance of 10m was measured out. It took the float 25 seconds to travel the 10m. Example 2 :20m distance was measured. Three floats were released. The time it took each of the floats was 18, 27 and 21 seconds. Calculate the average speed of the river. What is the advantage of repeating the experiment three times

Why put the float into the water in the middle and close the both banks?

SAMPLING So now you know what to do how do you choose your location! We call this sampling You are taking a sample of information from the river and applying what you find to the whole course. There are several types which do you use?

Types of sampling Point sampling Quadrat Transect

Which Sampling Technique? Use a technique that provides you with: –Most accurate results –Least effort –Appropriate sample size

Transect / Line Sampling Taking measurements along a line e.g. sample pebbles along a beach e.g. sample width of a river

Transect / Line Sampling e.g. measuring river depth across a stream

So go get wet!!!