Geology Reference
In-Depth Information
Table 9.12
Return period information from 1000-year WEPP run for the plough management system.
The comparable published precipitation return period information is also shown.
Return
period (y)
Runoff
volume (mm)
Sediment leaving
(t ha
−
1
)
Peak runoff rate
(m
3
s
−
1
)
Daily precipitation
(mm)
Published 24-h precipitation
for return periods (mm)
2
53
14.4
8.9
81
97 (
+
20%)
5
74
20.7
12.3
103
127 (
+
23%)
10
93
26.4
15.1
123
145 (
+
18%)
25
120
34.1
17.9
156
170 (
+
9%)
50
147
44.0
19.5
189
190 (
+
0.5%)
100
175
51.9
21.3
206
213 (
+
3%)
200
194
68.9
22.7
222
-
500
210
73.9
23.6
268
-
Table 9.12. In all cases, published values were
higher than those derived in this study, with
the largest differences occurring at shorter
return periods. The two- to ten-year published
return period estimates were about 20% greater
than those from this study, with differences at
the 25-100 year return periods being much
smaller.
practice in this region. Additionally, much of the
area in this region is in permanent perennial
grass. Hence, additional practices were not evalu-
ated. Practices that could have been evaluated
using WEPP include terracing, grassed water-
ways, buffer strips and sedimentation basins.
Additionally, variations in the management sys-
tems used could have been evaluated.
A frequent use of erosion prediction on agri-
cultural lands is the evaluation of different man-
agement systems. WEPP has a 'project set'
feature that allows for the evaluation of a
number of managements simultaneously. It has
been used in the Iowa Daily Erosion Project
(Cruse
et al
., 2006) to compute soil erosion every
day from 17,848 different locations in Iowa, each
with a unique combination of climate, topogra-
phy, soil and management, in one setup. It is
particularly useful when evaluating a number of
standard management practices for a particular
piece of land.
9.5.4
Identification of problem areas
The information shown in Table 9.11 indicates
that the hillslopes generate most of the sediment,
and that those management practices that have
considerable tillage have high soil losses. While
average slopes are small, slopes are quite long,
and all hillslopes have areas of appreciable slope.
Additionally, both annual precipitation and rain-
fall intensities are quite high.
The channels were susceptible to some deposi-
tion for the plough and chisel systems, and a
minor amount of erosion was predicted in the
channels when no-till and perennial grass was
used. Reducing the slope of the channel, and/or
widening it, would be expected to increase depo-
sition and reduce erosion in the channels. Using
grass in the channels for the corn-wheat-soybean
rotation would be expected to increase deposition
and reduce sediment delivery.
No-till has been shown to reduce the need for
conservation practices, and it is a very acceptable
9.5.5 Climate change
The effect of climate change on average runoff
volume and sediment yield is shown in Fig. 9.5.
These were all evaluated for the Fort Scott cli-
mate, using the WEPPCAT tool (http://typhoon.
tucson.ars.ag.gov/weppcat/index.php) to adjust the
Cligen parameter files for rainfall intensification
and precipitation increases of 5%, 10% and 20%.
