River darkwater

Aim of physical investigation

Carry out an investigation to see how a river changes as you travel downstream, and whether changes are what experts expect

Hypothesis of physical investigation

The key characteristics of the River Darkwater changes as we move downstream from source

Describe the location of the physical fieldwork

• Hampshire of South England

• River flows from North to South

• Source is in the hills of New Forest and its mouth is in the Solent

• The river flows 9km from moorland through a deciduous woodland to sea.

4 sampling sites

Holbury Mill Pond, Kings Copse, Gatewood Bridge, Lepe

Which model visually displays some of the key characteristics?

The Bradshaw model as it shows how we EXPECT the river to change as we move downstream

Characteristics investigated

River profile of Depth, Width, CSA, Pebble size and Roundness, and Velocity

Why was LOCATION suitable for river study?

why was RIVER suitable for study?

• Long enough (8km) to see change in data

• small enough to measure multiple sites in one day

• easily accessible, not too deep

Risk assessment

Medium for all, including drowning, trips and falls, and adverse weather

How to measure river width and depth (stratified)

• Place tape measure between river edges

• Place metre ruler on river bed

• Measure the width along 3 equal sites

• Measure the depth from the bed to the top of the water

• Repeat three times

Measuring river velocity

• use tape measure to measure 2m upstream from the width measurement

• Place rubber duck at the start of the tape measure and start the timer

• Stop the timer when rubber duck reaches 2m

• Repeat 3 times to get average

Measuring river bedload

• At the centre, grab bedload and place on clipboard

• Choose five random stones closest to the bottom of the clipboard

• Measure longest pebble in cm to compare to Power Roundness Chart on clipboard

Width results

Increased 3 times (2.2m to 6m)

River depth result

Increased 3 times (0.1 to 0.3)

CSA result

Increased 8 times (0.2m² to 1.6m²)

Pebble roundness and size results

Inconsistent pebble roundness while pebble size remained the same

Velocity results

Remained similar (0.2m/s)

Hypothesis results

Correct, except pebble roundness, size, and velocity, disagreeing with the Bradshaw Model

Data representation

Line graph of cross profile/cross sectional area, Scatter Graph

Line graph description

• 1cm = 50cm

• X axis (distance from source in km) on TOP, Y axis going down

• Y axis (depth to bed in km)

• Good because visual representation and CSA

• Bad because relies on accurate measurements and can be altered by anomaly

Scatter graph description

• Y axis is average velocity in m/s (0.1m/s per cm)

• X axis is distance from source (1cm = 1km)

• Good bc can see correlation, analysis of relationship, all sites on one graph

• Bad bc limited sites means limited data, so less valid