# How do river characteristics vary downstream?

How do river characteristics vary downstream?

To investigate how river characteristics vary downstream, a study took place over 1-3rd October ’03, on the River Lyd, concentrating on the stretch that flows through Parkend in the Forest Of Dean.

The aim of the exercise was to look mainly at both the Velocity and Cross Sectional Area, comparing and studying the data, but also Hydraulic radius, wetted perimeter and the physical geographical features of the river, looking for any significant differences as the river flowed downstream.

Above: [fig.1] Map showing River Lyd & investigation sites

To begin the investigation, it was decided that information from 12 sites would to be recorded and these sites were to be set 100m apart and each site would cover a distance of 10m.

Equipment used included:

• 3 range poles - steepness of riverbed and depth
• Stop watch – timing pooh stick
• Clinometer – Angle of slope of the riverbed
• Pooh stick / Orange - calculating velocity
• Tape measure – cross sectional area

## Method

1. Insert the range poles across the riverbed at equal distances (left, centre and right), measure the depth at each and calculate an average. Taking these measurements at each site gives data on the average depth of the river along its course, and will show whether the distance from the source affects the rivers depth.
2. Take the tape measure across the width of the river, from where the water touches the bank and take a measurement. As with the depth data, taking width measurements of the River Lyd will help to answer our investigation title, while combining the width with the av. depth will make it possible to calculate the wetted perimeter.
3. Measure the 10m stretch of river studying and insert on range pole in the bed at the upper most point and one at the lowest. Use the clinometer to observe the steepness of the angle from the riverbed.
4. To record the velocity, drop the pooh stick at the upper range pole and time how long it takes to travel downstream 10m to the lower range pole, take 3 readings along the course, so the effect of any obstacles or difficulties can be taken account of, and then an average calculated. With this average, the discharge for the site can be calculated after being combined with the C.S.A, these results will show how fast the river is flowing past the bank at that point and how much water is flowing through the area.

The most effective way of showing and analysing results is either by scatter graphs or Spearman’s rank correlation.

Scatter graphs present the relationship between two sets of variables, while also showing whether the results have a positive or negative correlation.

Spearman’s rank correlation portrays data in the correct order, as well as displaying the strength and reliability of the order. It gives a value, between -1 and 1, which describes the correlation between two sets of data.

## ‘The depth of the river will increase downstream’

Spearman’s rank ...