Geology Reference
In-Depth Information
0.18
200
180
0.16
Total sediment (kg)
Rainfall (mm)
160
0.14
140
0.12
120
0.1
100
0.08
80
0.06
60
0.04
40
0.02
20
0
0
Fig. 13.1
Relationship
between sedimentation at
Site 2 and rainfall.
Jan-
05
Feb-
05
Mar-
05
Apr-
05
May-
05
Jun-
05
Jul-05
Aug-
05
Sep-
05
Oct-
05
Nov-
05
Dec-
05
Jan-
06
Feb-
06
Mar-
06
Apr-
06
May-
06
Month
Table 13.1
Sediment collected on the astroturf mats.
Sediment deposition in each observation period (g cm
−2
)
Site
Number of mats installed
Jan-Apr 2005
Apr-Jul 2005
Jul-Oct 2005
Oct-Jan 2005
Jan-May 2005
Total
1
10
0
0
0
0.62
0
0.62
2
12
5.79
1.51
0
0.01
0
7.31
in April, July and October 2005, and January and
May 2006. Between 1 February 2005 and 30 April
2006 there were 112 rain days and 3718 mm of
rain recorded in the Somerset area; this included a
number of heavy rainfall events, for example, over
25 mm of rainfall on 24 and 28 June 2005. Overall
there is a clear relationship between rainfall and
sediment deposition, with most of the deposition
occurring following the highest rainfall amounts
(Fig. 13.1). At the first site, the land dipped slightly
towards the centre of the field, indicating an area
where flow was likely to concentrate before enter-
ing the buffer. Ten mats were placed in the buffer
at this point of which five collected sediment,
two at the front, one in the middle and two at the
back of the buffer. Deposition was measured only
in January 2006 when the field was bare. The land
was under maize in the summer of 2005 and field
beans in the spring of 2006.
In the second field, 12 mats were located at the
base of the gully, six in the corner of the field
below the farm tracks, and six in a sedimentation
area at the field edge. Sediment was collected
from mats at the front, middle and back of the
buffer in the first and second locations in the first,
second and fourth measurement periods. The
step at the field edge prevented sediment from
reaching the mats at the third location.
At the end of each observation period, the mats
containing sediment were removed and replaced.
The mats taken from the field were placed in plas-
tic bags and transferred to the laboratory where
