Where does water come from? Rain is one of them and one of the largest sources of water on earth. It is a liquid manifestation (other prescriptions that are not liquid such as snow, ice crystals, and slit). Water droplets that fall on land due to the process of condensation of water vapor in the atmosphere are then called rain. The type of rain that falls is divided into several types depending on how the process is formed, including frontal rain, orographic rain, artificial rain, and convection rain. In this chapter what we will discuss is orographic rain, according to the process of formation that is part of the River Basin.
Orographic rain or well-known people with rain that occurs in the mountains, is rain which the process occurs due to an increase in air containing water vapor from the valley to the top for wind assistance that is dry (wind fohn). The air that rises to the top and contains water vapor will cause a decrease in temperature on the mountain and then condense to eventually cause rain on the slopes.
The connection with water travel in the watershed ecosystem, the grains of rainwater that falls on the slope do not fall directly to the ground but are held in the canopy of trees in the mountain valleys. Then the water seeped down from the leaves, into the branches and branches soaking all parts of the tree, down again until it reaches the roots and settled into the ground as groundwater reserves and form a layer of aquifers. Groundwater, both deep groundwater (artesian) and shallow groundwater, is the main source of water availability in a watershed ecosystem, as a provider of clean water, a source of drinking water along with the necessities of human life, as irrigation for paddy fields, as generator electricity and also as a natural laboratory.
But the story will be different if the water that falls from an orographic rain is not held up by a tree canopy so that the water that falls directly hits the ground. Rainwater has the property of damaging or eroding when it occurs in large numbers and directly splashes on the ground causing erosion. Erosion caused by this occurs because rainwater which directly splashes on the soil or rocks will erode the soil or rock so that the material is soft and easily destroyed. If the material is soft and easily destroyed, then the rainwater journey that ensues then continues into the flow of material both soil and rock down from the mountains (upper watershed) to the area below, until it empties into the coastal areas.