Hi everyone,

From today’s lesion, we were continuing to discuss about the drainage basin which is an essential part of hydrological cycle. To help us have a better understanding of it, we were brought downstairs behind TC block to see how the whole system looks like. By definition, a drainage basin is not only a river. Instead, it is the area that is drained by a main river and its tributaries. Those tributaries are always from higher altitude because water flows down due to the gravity by the earth. They contribute to the main river.

However, drainage basin is not only the water-flow. It refers to the area that is drained. Those areas are always covered by vegetation. Water does not flow very fast because of the existence of vegetation and soil.
Vegetation reduces the rate of the entire hydrological cycle because IT CAN STORE WATER. Hence less (Slower rate of the hydrological cycle is not the same as less water in the system) water will flow into the system. Different vegetation will result in different interception of water. Those huge rainforest will store more water than grass.

Vegetation also prevent the lost(loss) of soil. When soil is saturated, the excess water will bring the soil the river. It causes the lost of soil and an increasing level of river. Vegetation will store the excess water and hold the soil more tightened. Another factor that affects soil moisture is temperature. During summer, high sunlight density and higher temperature will let soil evaporate more water while water tends to remain during winter. (Are you sure?)

So far, we have discussed about the drainage basin and its river and how the vegetation zone store water. But why is water so important?

The main idea is that life needs a LIQUID MEDIUM to transporting the molecules that are necessary for its existence. Water is the main liquid in the earth.

How does water’s property help remain lives? The key is to understand the structure of water-------hydrogen bonding. Firstly, it becomes less dense as it freezes. It allows the ice float up to block the cold temperature from air keep freezing the water. Aquatic life hence can survive during cold weather. Secondly, it allows water to remain liquid state over a large range of temperature. That means it will not change its property of conducting molecule transporting easily(Liquids transport molecules far more effectively than Solids or Gases. Water stays as a liquid over a wide range of temperature). Thirdly, it makes water have high specific heat. It allows water remain in a stable range of temperature even absorbing a large amount of energy(Back to the question, water helps keep the body temperature constant). Furthermore, hydrogen bonding plays the role in reproducing and evolving life. It helps the 2 DNA strands bond together.

Nonetheless, water also other characters also helps maintaining life on Earth. It can dissolve materials (Chemicals? Compounds?) to assist in transporting molecules. The clouds also help block out harmful UV light. ( Ozone layer does, Clouds and dust only absorb heat)

Just a short revising,

Drainage basin contains 2 parts: River and its tributaries, the area drained.
The importance of vegetation zone: containing water (Should be reducing overlandflow by delaying the water flow and providing another pathway for water which is transpiration)
The importance of water: Hydrogen-bond (high specific heat(How do you know that H bond is responsible for it since H bond is not a strong bond?), large temperature range, DNA bonding) and other characters (perfect solvent, UV light blocker (Water never blocks UV light =.=), etc)

Comments made by Minh.
Lignum Rocks.

Cai Yida/27 March