The document discusses the necessity and techniques for measuring soil loss in agricultural watersheds, emphasizing the importance of such measurements for soil and water conservation practices. It details various methods including runoff plots and sediment samplers for assessing soil erosion and informs on the types and designs of these plots. Additionally, it addresses the merits and demerits of runoff plots and explains two specific sediment sampling methods: multislot divisor and coshocton wheel sampler.

1. SOIL LOSS MEASUREMENT
TECHNIQUES
Lecture-5
Dr. Ajay Singh Lodhi
Assistant Professor
College of Agriculture, Balaghat (M.P.)
Jawahar Lal Krishi Vishwa Vidyalaya, Jabalpur (M.P.)

2. NEED OF SOIL LOSS MEASUREMENT
 Measurement of soil losses from agricultural watersheds is necessary to know
 The influence of soil and water conservation practices in the area and
 Take appropriate measures to prevent serious consequences.
 Information generated by the studies on soil loss is used to develop relationships which
could be used to predict the soil loss under different soil and crop management practices.
 It is helpful for
 Design of soil conservation measures
 Design of Dam and Reservoirs
 Design of Stable Channels

3. SOIL LOSS MEASUREMENT
Soil loss measurements could be done through
 Runoff Plots
 Sediment Samplers
When we use Runoff Plots
 For demonstration of farmers
 For comparative studies
 To obtain data for validation of models to
predict
 Runoff
 Sediment
Runoff Plots

4. DIFFERENT TYPES OF RUNOFF PLOTS
Based on Structure of Plots
 Natural or simulated rainfall feeded plots
 Bounded or unbounded plots
Simulated rainfall feeded Bounded Plots

5. DIFFERENT TYPES OF RUNOFF PLOTS
Based on Size of the Plots
 Micro Plots
 Medium or USLE Plots
 Large Plots or Watersheds
Micro Plots
 The size of micro plots can vary from 0.05
to about 2 m2.
 Frequently used in laboratory experiments
under simulated rainfall conditions.
 Particularly suitable for studying inter-rill
erosion.

6. DIFFERENT TYPES OF RUNOFF PLOTS
Medium or USLE Plots
 22.13 m length, up to 4 m width and 9 per cent slope is the standard
requirement of a standard USLE plot (minimum width should be 2m).
 They are used for the validation of the USLE model.

7. DIFFERENT TYPES OF RUNOFF PLOTS
Large Runoff Plots or Watersheds
 The size of these plots could be at least 100
square meters.
 These are suitable for studying the
combined process of rill erosion, inter-rill
erosion and gully erosion.
 These plots represent the sample of
landscape and capture of different erosion
phases.

8. MERITS AND DEMERITS OF RUNOFF PLOTS
Merits
 Useful in assessing the magnitude or severity of erosion and its effect on soil
productivity.
 Useful in designing and establishing erosion control practices.
Demerits
 These are expensive for both initial construction and maintenance.
 Huge number of labour is required.
 Problems of collecting samples and recording the soil, and water data.

9. SEDIMENT SAMPLER
 Sediment samplers are basically used to collect sediment-laden water samples
from a flowing water body (river, tributary, canal etc.).
 These sample is subjected to laboratory analysis to determining the chemical,
physical, toxicological or biological composition of the sediment.
 Samples are also used to collect scoops or cores of soil from a known silt
deposition site, for example, reservoir bottom flood plain, to gather historical
information.
SEDIMENT SAMPLING METHODS
 Slot Sampling
 Grab Sampling

10. SLOT SAMPLING
 Slot samplers are used in any erosion studies from
small test plots to the watershed of several square
kilometres.
 These samplers are typically automatic, and no
observer is required during the operation.
 The sampling could continue under heavy runoff
events.
Two main types of slots samplers are
 Multislot divisor and
 Coshocton-wheel sampler

11. MULTISLOT DIVISOR
 The multislot divisor was developed by R.V. Geib for collection of the runoff
water from small plots of sizes from 1/125 to 1/250 ha.
 The divisor is provided with a number of slots of equal dimensions.
 It is fitted at the end of a rectangular box through which the runoff water from a
stilling tank passes with a uniform horizontal velocity.
 The flow gets divided into equal parts on passing through the slots.
 Only the flow passing through the central slot is considered, which is let into a
collecting tank, and the rest of the flow is allowed to drain away.

12. MULTISLOT DIVISOR
 The runoff from the plot is at first collected in a structure, called the collector,
from where it is guided to a stilling tank to dissipate the energy of the runoff
water.
 A relatively tranquil water now enters the multislot divisor, and then from the
central slot of the divisor to a storage tank.
 The water from the storage tank is collected and analysed for sediment
concentration.

13. COSHOCTON WHEEL SAMPLER
 Coshocton wheel sampler was developed at place in the
USA known as Coshocton.
 The runoff discharge through a H-flume or a triangular
notch is allowed to fall upon a water wheel which has a
sampling head, with a slot along its top, mounted on it.
 The wheel slightly inclined, therefore, causing the wheel
to rotate.
 During each revolution of the wheel, the slot cuts across
the jet of water falling from the flume collects a portion of
it and passes this runoff water vertically downwards into
a collection pan, from where the water sample is carried
to a storage tank through a conduit.
 Coshocton-type runoff sampler useful to collects the
runoff from test plots or natural watersheds.

14. Thank You