A study of the Mae Ai River in Northern Thailand
Introduction
You will be studying the characteristics of the Mae Ai River, which is about 8km from Ban Tha
Ton. The first study site is a few km from the river’s source, which is in a watershed of natural
forest on the Burmese border. At this site, the river emerges from a steep sided gorge which
contains rapids and waterfalls, but which is only accessible by difficult walking through dense
jungle. From this location, the river flows through intensively cultivated agricultural areas and
then through the town of Mae Ai itself. The last location is just before the town.
The aim of the fieldwork is to study the hydrological and fluvial characteristics of the river and
to see if it ‘behaves’ like a normal river!
Pre-visit discussion
All rivers should have the same patterns of flow and other fluvial features. From your studies,
you should know about these patterns and features and how they change as the river flows
from the upper sections of a river to the lower course. These characteristics are generally
easily observed and measured.
1. a) in the first column of the table below, make a list of the features and flow
characteristics you should be able to observe and/or measure .
b) In the second column, describe the expected changes. Try and describe the
change as if you were writing an hypothesis.
Features and Flow Characteristics
River discharge
Expected Changes
The discharge of the river should increase with distance
downstream.
The Fieldwork
At various sites you will be required to conduct the following work.
 Calculate river discharge by finding the average velocity and cross sectional area
 Measure bedload – size and shape
 Measure channel gradient
 Make observations and take notes about aspects of the river valley
Equipment
Digital flowmeter; stopwatch; tape measure; ruler; clinometer; spirit levels; ranging poles,
record sheets.
1. River discharge
In order to find the discharge of the river, we need to find the cross sectional area and
average velocity.
A Cross Sectional Area
 At intervals across the river measure the depth using the ranging poles / rulers. The
interval would depend upon the width of the river. The cross sectional area can then be
calculated.
B
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Velocity
Calculate the average velocity of the river using the ‘flowmeter’ devices. Carry out
measurements at several places across the river – the number of places will depend on
the width of the river. Time the number of revolutions over a 60-second period and use
the formula to calculate the velocity.
Use the data for the cross sectional area to calculate the average discharge, using the
formula provided for you on the Discharge Data Sheet.
2. River gradient
Use ranging poles, tape measures, spirit levels and a clinometer,
measurements over 5 to 10 metre units.
take several gradient
3. Bedload characteristics
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You should select 10 bedload samples. This can be done with a ‘systematic-random’
method. This is done by laying the tape measure along the river channel from one side to
the other to a length of about 10 metres.
At metre intervals, ‘blindly’ select a bedload sample.
Measure their long and short axis and note their shape using the Power’s Scale of
Roundness.
4. Observations
At each location, it is important to note down features of the valley (size, shape of the valley
floor and valley sides etc) and the river (take photos of course) and also to make notes about
other features such as vegetation
Follow up work
A large number of calculations will need to be carried out to find out downstream changes in
a) velocity b) cross sectional area c) discharge d) gradient e) bedload.
These findings can be graphed, changes observed and hypotheses looked at again to see if
they were correct or not.