The Changes in Loughton Brook as it Moves Downstream

In the past, the area was used as a Royal Hunting Forest, but was also used by local people for grazing and as a source of fire wood. Approximately two thirds of the forest is wooded, and the trees were pollarded. This means that they were cut a few feet above ground level to allow timber removal while the animals continued to graze underneath. Pollarding ceased in 1878 when the Epping Forest Act appointed the Corporation of the City of London as Conservators of the forest. Since then the forest has been protected for its wildlife interest and as a place for recreation.

The highest point within the Loughton Brook drainage basin is at High Beach which is at 112m above sea level. The lowest point is at 17m and it is where Loughton Brook forms a confluence with the River Roding.

The drainage basin of Loughton Brook is 5.6km2 in total. This consists of 2.2km2 of urban catchment and 3.4km2 of forest catchment.

The geology of the complete area consists of alluvium, glacial gravel, pebble gravel, bagshot beds, claygate beds and London clay. The map below demonstrates this more clearly.

My first hypothesis is that the width, depth, and velocity of the river will increase as it moves downstream.

I think this will happen because river discharge usually increases downstream due to the drainage basin becoming bigger, and therefore the volume of water reaching the channel via tributaries, surface flow, through flow, and groundwater flow increasing. I think that the velocity will increase downstream due to the decrease in number of pebbles and rocks. As the pebbles decrease in number and size, friction also decreases. This means that the river has more energy to flow. My second hypothesis deals more with this issue.

My second hypothesis is that the shape and size of pebbles will decline as the river moves downstream.

At the source of the river, the pebbles will be very angular and larger but downstream they will be much smoother and smaller. This is because the river smoothes the pebbles and wears them away as it transports them downstream before depositing them. Transportation occurs through traction, saltation, suspension and solution. The longer that they have been transported, the smoother they are as they have spent the maximum time in the water being rounded. This hypothesis is linked directly to my first one as a river uses the transported material to erode its bank and bed. As the velocity of a river increases, so too does the load it can carry and the rate at which it can erode. A river may erode by one of four processes: Attrition, hydraulic action, corrasion and corrosion.

My final hypothesis is that the river floods downstream more than upstream.

Flooding is a normal occurrence in the lower course of a river and is why a flood plain is created. A flood occurs when the water in a river overflows out of its banks and leaves the channel. Deposition is often a major factor of flooding. This occurs when a river lacks enough energy to carry its load. Deposition, beginning with the heaviest material first, can occur following a dry spell when the discharge and velocity of the river drop, or where the current slows down. However, flooding can also occur during a wet period when there is simply too much water in the channel. This aspect of my project is related to both physical and human geography as I have also researched the affect of flooding on the local people's homes and businesses.

To observe the changes of the river as it moves downstream, I visited three sites along Loughton Brook. The first site was up stream, the second mid stream and the third down stream. I also visited a fourth site which has been artificially straightened to transport the water into the local town. At the first three sites I measured exactly the same things so that I could easily compare them and note the differences that occur as the river travels along its course.