CHAPTER 4: HYDROLOGIC CYCLE

INTRODUCTION

The hydrologic cycle is the emotion from the ground to the atmosphere and back again. There are many process that involve in hydrologic cycle. The most important part is evaporation, transpiration, condensation, precipitation and surface runoff.

HYDROLOGIC CYCLE PROCESS

The first step is the change of state of a substance from liquid to gas. For evaporation occur, the energy is required. The energy can come from many sources such as sun, atmosphere and earth. When water evaporate it is raising to atmosphere.

At the same time, similar step is occur it is called transpiration. Which it is the evaporation from the plants. It is controlled by the humidity of the atmosphere. When the raising of the water vapour to the atmosphere, condensation is occur. At which it is the change of water vapour to atmosphere change into liquid state. In the atmosphere, condensation appears cloud.

In the next step, it is called precipitation. It begin with the water vapour is condense in the atmosphere and then become too heavy to remain at the atmosphere and falls in the form of sleet, rain and snow.

Next, in the final hydrologic cycle is called surface runoff. The runoff occur when there is an excessive precipitation on the ground that saturated which mean the soil cannot absorb any more water. Rivers and lake are result to runoff. Evaporation of this runoff to the atmosphere begins the hydrologic cycle over again. Hydrologic cycle help to consistency, it is carry nutrients and particular matter to plant, animal and environment.

Next, there is two more sub hydrologic cycle that involved, they are sublimation and deposition.

First, sublimation is the transition of solid phase to the gas phase. Based on the thermic, temperature and pressure an example could be dry ice, the room temperature and pressure is sublimate to the carbon dioxide.

Besides, the other is deposition, it is also known as sublimation. Where it is a gas transform into solid and it is the reverse of sublimation. When deposition is displaced by which itself freezing air, water vapour change directly into ice without first becoming a liquid, this is how snow form in cloud as well as frost.

With deposition to occur, thermal energy was removed from the gas when the object become colding off. The water vapour in the air surrounding, losses enough thermal energy to change into a solid without passing through liquid phase.

WATERSHED

What is watershed? Is it a shed that holds water? Nahh, try again.

Watershed is all of the land that is in the same location of bodies of water. People tend to think any water bodies such as rivers, lake and wetland. However, any lands whether it is park, farm, school parking lot is also included. Think about watershed is a fun of life, in all world had pacific area and draining into the nearest bodies of water.

Drop by drop, water flow in the soil, flow to the stream, and into larger and eventually to the ocean. Everyone in the earth lives in the watershed. Watershed knows no borders with the local, national and international.

EFFECT OF LAND USE TOWARDS THE HYDROLOGIC CYCLE

First is deforestation, trees store great quantities of water, especially in rain forests which are deforested the most. When those trees are cut down the water their store is lost.

Next is industrialization, manufacturing industries release large amount of carbon monoxide, hydrocarbons, organic compounds, and chemicals into the air thereby depleting the quality of air.

And the last effect is urbanization, when precipitation falls over the land, it follows various routes. Some of it evaporates, returning to the atmosphere, some seeps into the ground, and the remainder becomes surface water, traveling to oceans and lakes by way of rivers and streams.

HYDROLOGY CONTINUITY EQUATION

EXAMPLE 1

Assume:

            Infiltration = ø

Find the evaporation for ∆t.

Solution:

(P + Rin) - (E + Rout) = ∆S

Inflow – Outflow = ∆S

  

Solve for E,

E = Rin + P – Rout - ∆S

 

 

EXAMPLE 2

Given:

            Time Period, ∆t = 10 days

            Evaporation, E = 3.5 inch

            Precipitation, P = 7.0 inch

            Change in Storage, ∆S = -8 inch

Solve leak.

Solution:

P – (E + Leak) = ∆S

Inflow – Outflow = ∆S

Leak = P – E - ∆S

 

Example 3

The drainage area of the James River at Scottsville, Virginia, is 11839 km2. If the mean annual runoff is determined to be 144.4 m3/s and the average annual rainfall is 1.08m, estimate the ET losses for the area. How does this compare with the lake evaporation of 1 m/yr measured at Richmond, Virginia?

Assuming that ΔS = 0,

Runoff is converted from m³ to m/yr as follows