Soil Erosion Erosion pins

Method description: Erosion pins

The method of erosion pins is a standard technique to detect soil sheet and rill erosion. This widely used method consists of driving a pin into the soil so that the top of the pin gives a datum from which changes in the soil surface level can be measured. An example is provided in the figure below.

Figure 1 Pins combined with remote monitoring of rills. Photo © Maíra Ometto Bezerra

The pins can be of wood, iron or any material that will not rot or decay and is readily and cheaply available. The pin should be a length which can be pushed or driven into the soil to give a firm stable datum: 300 mm is typical, less for a shallow soil, more for a loose soil. A small diameter of about 3 mm is preferable, as thicker stakes could interfere with the surface flow and cause scour. A rectangular or square grid layout will give a random distribution of points with a spacing appropriate to the area being studied

Sampling design

Erosion pin can be installed in square grids according to the figure below or within the contours of rills and ephemeral gullies. A rebar benchmark can be installed on one of the square edges as reference point and the location of the benchmark estimated with GPS.

Figure 2 Diagram of erosion pin setup in square grid

For an area of one hectare, it is recommended to install at least ten square grids. If specific erosional features are being monitored, e.g., rill erosion and ephemeral gullies., sampling frequency depends on the number of features that are the subject of the study.

Quantification method to assess soil erosion

Measurements of pin expose are to be made every 3- months or after erosive or aggressive rainfall event (mm/3-months, or mm/ year, or mm/ 3-years).

Practitioner measures the height of the pin using a digital depth gauge or metal ruler. Relations are then empirically derived to quantify annual erosion rates.

Main costs

Main costs are provided in the table below.

Table 1. Main costs to estimate sheet erosion using the erosion pin method

Preparation for a field day

The basic for steps to prepare for a field day to survey erosion pins.

Figure 3 Basic tasks for a successful field day to characterize soil erosion using the pin method