Soil erosion is a major problem in Australia and around the world. Millions of tonnes of soil are lost every year by erosion from Australian agricultural lands, which result in diminished capacity of lands to produce our ever-increasing agricultural needs. A degree of understanding of the processes involved in soil erosion, and the impacts that human activities have on this otherwise natural phenomena, is necessary. This will assist students in environmental science, engineering and planning in looking after soil, the precious and non-renewable resource upon which all terrestrial lives depend. In this practical activity, students will carry out a number of simple erosion experiments in the flume of our rainfall simulating facility (GUTSR) to find out how the processes of soil erosion by rain and runoff work and how much soil will be lost if no soil conservation measure is in place. Then a simple soil conservation technique will be applied to the same soil in the flume and its effect on reducing soil erosion will be measured.
- To demonstrate the processes of soil erosion by rain on different slopes under a simulated rainfall events.
- To measure sediment concentration and soil loss by rainfall erosion with and without a conservation measure (10% surface contact cover) in the flume of the GUTSR facility and to extrapolate the results to field situation.
- To demonstrate the effectiveness of a surface contact cover in reducing soil erosion on a range of slopes.
A loamy soil of known characteristics has been put in the flume, levelled and prepared for experimentation. The soil is disturbed and in its present condition in the flume, it is highly erodible.
Experiments with and without protection
- 10 groups of 2 or more students will be formed in each session and a specific slope of 1 to 10% will be assigned to each group. Each group will pick up 2x500ml beakers, number them, weigh them on the coarse top-pan balance and record their weights in the second column of Table 1.
- The experiment on the simulated rainfall will start with the highest slope. Once the flow rate at the flume exit is stabilised, the Group for 10% slope (or the highest slope%) will collect the sediment and runoff using one of the 500 mL beakers and the time for sample collection will be recorded in column 3 of Table 1.
- The group must then take their collected sample into the lab and weigh it on the same coarse top-pan balance. This will give the weight of beaker + sediment + water which goes into column 5 of Table 1.
- Without stopping the rain, other groups, in the order of decreasing slope, will do steps 2 and 3 as well, collecting, timing and weighing their sediment + runoff samples.
- Metal or plastic plates (simulating plant residue contact cover) will then be dropped randomly on the surface of the soil to give a total of 10% surface cover.
- Steps 2 to 4 will be repeated with 10% surface cover.
- After visually observing the changes with slope of sediment concentration in the collected samples, the beakers will be transferred to an oven for overnight drying.
- Students will need to come back to the lab 24 hours later and weigh their dried sample (beaker + dry sediment) and put the dry weight of soil + beaker in column 6 of Table 1.
- Then find the amount of eroded soil by subtracting column 2 from 6 and put it in column 7.
- Calculate sediment concentration for your assigned slope as g/l and soil loss as grams per m2 per hour (g/ m2/hour). Enter your results in columns 8 and 9 of Table 1.
Data handling and analysis of experimental results
- Students from the session will combine their data and compose a Group Table so that the data for all slopes can be plotted on graphs by all students.
- So, once students have calculated their individual data at their selected slope in Table 1, they will need to transfer their results from the last two columns of Table 1 into the large Group Table 2 sheet which will be put next to the drying oven. They will be clearly labelled for each session with session number and time and day of the session (please mke sure you don’t put your data in the wrong table). Once this Group Table is completed by all students of each session, it will be edited by the tutors to remove wrong and misleading data and uploaded on the course site for the session members to use and plot their graphs and prepare their reports. It is therefore very important that all students in the session complete their measurement and calculation and enter their data in the large table to produce a full data set for everyone to use.
- Students will download the Group Table data from the Portal and then use Excel (or any other graphic program) to produce a graph by plotting the sediment concentration against slope for rain-no cover and rain + cover in one graph. Use the X-Y scatter point option in Excel and put a line/curve of best fit into those data points. No other form of graph is accepted.
- Plot a second graph of soil-loss against slope for rain-no cover and rain + cover in another graph (plotting procedure is the same step 3 above).
- Discuss the effect of slope and surface contact cover on sediment concentration and soil loss, as shown on the above two graphs.
Table 1: Individual results
Name: Omar AL Balushi… Student No: ALOAD1701….Slope: 10 %
Date:15/11/2017. Names of the other students working with you on this slope: Kevin
|Experiment||Beaker weight (g)||Collection time (sec)||Sample volume (mL)||Beaker + wet sample (g)||Beaker + dry sample (g)||Dry weight of sediment collected (g)||Sediment conc. (g/L)||Soil loss (g/m2/hour)|
|Rain, no cover
Table 2: Group results
Session No: 10 Time: 11:45 AM. Date: 15/11/2017
|Sediment Concentration (g/L)||Soil loss (g/m2/hour)|
- How effective has the 10% contact cover been in reducing soil erosion by rainfall?
- On what slope the cover was most effective in reducing rainfall erosion?
- What was the effect of slope on sediment concentration and soil loss?
- Discuss the interaction between slope and surface contact cover on soil loss and sediment concentration.
For the interaction between slope on soil loss