EVAPORATION
Crucial for the future
Ever one knows what evaporation is but there are not a lot of people that know what influence it has on the natural water sources that we have. There are a few interesting ways to measure evaporation and we will be looking at a few instruments that are used for the measurement of evaporation.
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TYPES OF MEASURING EQUIPMENT:
​Class A evaporation pan:​
The Class A evaporation pan is used to measure the amount of water that evaporates in a set time period. This pan is made of galvanised iron which is welded to maintain its shape as well as keeping it watertight. The dimensions are fixed to keep the test standard. It is 255mm deep and has a diameter of 1207mm. It is normally installed on a wooden platform on the ground in a grassy area where it is exposed to the elements with no trees in close proximity to the pan that can prevent wind from influencing the results. The pan is filled with water and exposed to the elements to represent an open body of water. The pan is filled to a datum in the fixed point gauge and then readings are taken every 24 hours.
(Hydrological services PTY LTD 2003)
Atmometer:
The atmometer or evaporimeter is a scientific instrument used for measuring the rate of evaporation from a wet surface to the atmosphere. The instrument is set up by using a porous plate like object like filter paper, which can draw water from a graduated cylinder via a wick of some sort. As water evaporates from the surface, it tends to draw more water from the source through the wick by capillary action to replace the water lost by evaporation. By periodic measurements of the quantity of water remaining in the graduated cylinder, a rate of evaporation can be established. By also using the surface area of the plate we can establish a rate of evaporation per unit area.
(Wikipedia 2012)
Symons evaporation tank or S-tank:
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The Symons pan is also known as the sunken Colorado pan. It is different from the class A pan in the sense that it is a squire shaped pan where the sides are 1m wide and it is 0.5m deep. This pan is sunken in to the ground to a depth of 450mm so that the top of the pan protrudes the soil by 50mm and placed on the top of a concrete slab. The pan is made of unpainted galvanised steel and welded to make sure that the pan is watertight. The pan is then painted black. The problem with this set up is that it is very hard to trace ore determine leakage.
(Wikipedia 2012)
