Rain Water: Technical Introduction and Literature Review

In civil engineering field we have to consider not only structural elements, bridges, highways, railways etc. but also field of water and environmental. When we consider about water resource. Especially it is very essential resource in day to day life and also at the future that because of its demand because of sustainability. And also when we think about ethically also we should pay our attention not only for using but also for protecting this resource and get maximum usages. There are some methods to protect water resource and reusing this resource. Rain water harvesting is one of best method to protect this water resource. Actually there are mainly two methods for rain water harvesting. Run off harvesting and rooftop harvesting. Rainfall intensity is that amount of water that fall from period of time. When we talking about this situation of Sri Lanka. According to the data released by irrigation department in 2017 data are as follows

• 103 river basins
• Major catchment areas Mahaweli-1027sq Km
• Walawe -2442Sq km
• Kalu -2772 sq km
• Average annual rainfall -1861mm
• Rainfall volume annually -12x1010 m3
• (IRRIGATION DEPARTMENT DATA IN 2017)
• Sri Lanka as a tropical country mainly gets rain from three basic ways.
• Monsoons North-Eastern monsoon
• South-Western monsoon
• Convective
• Cyclonic

Hence harvesting rain water is very important criteria because according to the annual rainfall 12x1010 m3,we are using very less amount of water. Since the past period Sri Lanka had paid attention for this case. Once upon a time the king prakkramabahu had said that “Don’t let to very few amount of water from sky without using direct to sea. When we consider about harvesting method, it is defined as storing in such way that it can be used at future. For harvesting method we should have proper catchment, it is a best method using roof top harvesting and using it for domestic and agriculture works.

In Sri Lanka, as in the world a water scarcity is experienced now days. The rainfall patterns have been confounded. People in the rural areas don’t have pipe borne water.

The natural water resources aren’t qualitatively and quantitatively possible to fulfill the water demand. The drinking water issue has been so much critical as hundreds of people get died because of the CKDu problem in the North Central province consuming poor quality water. Therefore, Rain Water Harvesting is a better solution to overcome these issues. Due to the increment of human population their basic needs also have been prominent. Therefore, the demand of drinking water is increasing day by day. However, nature was able to provide the amount of pure natural water to mankind. But after the industrial revolution and through the development of new technologies caring of environment was abundant by the mankind. Water was greedily used by some nations for their industrial purposes by some nations while some nations suffering from a water scarcity. It occurred so many natural disasters in the world. The climatic patterns were changed.

Environmental issues such as global warming were taken place. The natural water resources were polluted because of the industrial waste was discharged into the surface water resources without any treatment. The water quality of them was decreased rapidly. Therefore, the amount of natural water resources was not enough to fulfill the demand of drinking water for every human being equally and efficiently. Even though there are plenty of water resources on this earth only a mighty percentage is suitable for drinking. That drop of water also has been polluted by the man. A water scarcity has been created on this planet not because of any living being but because of mankind. According to United Nations Department of Economic and Social Affairs around 700 million people in 43 countries suffer today from water scarcity today. By 2025, 1.8 billion people will be living in countries or regions with absolute water scarcity, and two-thirds of the world's population could be living under water stressed conditions. Some people have to walk hundreds of miles to find a simple amount of water to drink.

People tend to drink polluted water to fulfill their need of drinking water with the water they had. It is not suitable for potable consumption. But they have to find water any how to fulfill the thirst. As a result of consuming that polluted water they were suffered with so many water born and water related diseases. Thousands of children and adults died because of consuming that polluted water without treating. It has been found that the reason for the CKDu problem is also consuming polluted water contaminated with heavy metals. Then people tend to find solutions for this water scarcity and to save the mankind from this burning issue. As one method rain water harvesting can be obtained. It is defined as storing in such a way that it can be reused at future. For harvesting method we should have proper catchment, mainly two methods for harvesting runoff harvesting and rooftop harvesting, Roof top harvesting is a good method not only for domestic but also for agriculture. There are some factors that should be considered at the level of rooftop rain water harvesting

When consider about situation of Sri Lanka, In June 2005, the government of Sri Lanka adopted the “National Rainwater Harvesting Policy & Strategies” under the objective of encouraging communities to control water near its source by harvesting rain water. As a result, additional water security, minimizing the use of treated water for secondary purposes, reduction of flooding, improving soil conservation and groundwater recharge, providing water for domestic use with adequate treatment, agricultural benefits and reduce energy consumption were targeted. In addition to the policy, a regulation was gazette on 17th April 2009, which makes rainwater harvesting mandatory in certain categories of new buildings in areas under municipal and urban council jurisdiction, As a result, rainwater harvesting systems were installed in several places in Sri Lanka and they were from different kind of rainwater harvesting tank materials. And also, they would be either above ground or below ground or alternatively.

Even though it is widely used in the dry zone there are some issues exist in the rainwater harvesting systems in Sri Lanka. Quality of stored rainwater is one single factor that threatens the sustainability of RWH technology. Many users do not use rainwater for consumption purposes due to the notion that it is unfit to drink. That is because of various issues existing in the rainwater harvesting systems in Sri Lanka

There are some factors affecting for rainwater harvesting at roof top.

Issues and Factors Affect For Rainwater Harvesting Of Commercial Building

Age of roof sheet-With the age of the roof the degrading of roofing material would be taken place in a higher rate. It is just because of the roofing material is exposed to various weather and climatic conditions with its age and the chemical composition of the material would be changed due to that. And also, different rains would have different chemical compositions. As an example, PH values would be different. Then the degrading of roofing material would be accelerated or de accelerated depending on the rain water composition with its age. And also with the age of the roof the degrading of roofing material increases and therefore the solid loads would be increased. The solids may include particals of roofing material.

Roofing Material

It has been proved that the roofing material affects the water quality of the roof run-off directly. The chemical compounds of the roofing material would be de composed and mixed with roof runoff. Some chemical compounds would be toxic and some contaminant levels would be not complying with the drinking water standards. But there isn’t any conclusion that a specific roofing material for Rain Water Harvesting.

Land use Pattern

It is obvious that the urban areas are more polluted than the semi urban or rural areas. The rain water quality would also be the same. In the urban areas air is contaminated with lots of toxic compounds which is hazardous to the human health. And also, the roof tops would be deposited with heavy metals, toxic compounds and inorganic compounds through atmospheric deposition, direct contact and through animals. But in rural areas the scenario would be different than the urban areas. The environment would not be polluted than the urban areas. The roof run-off quality would also imply the same situation.

Rainfall intensity and duration

When the intensity of rainfall is low the water quality of the roof run-off would be lower than the water quality of roof run-off from a higher intensity rainfall. Mainly it is just because of the first flush. The pollutant particles would not be removed with the first flush when the rainfall intensity is low. The ability to wash of pollutants on the roof and gutters will be reduced when the intensity and the duration of the rainfall is low

Weather conditions

The temperature, rainfall pattern and the antecedent dry period also have effects on the water quality of roof run-off. The roof run-off after a huge dry period contains more pollutants than the roof runoff from a frequent rainfall. During the dry period the air contaminates with so much of pollutants and also the rooftop through atmospheric deposition. Then with the rain those pollutants mixed in rainwater and have water quality issues in the roof run-off

Mosquito and insect breeding can be minimized by regular cleaning of gutters and closing the water tanks securely. One of the contributory factors in this regard is the heavy weight of the tank cover. As such, women, who are the main users of rainwater, found it difficult to manipulate the tank cover every time they need water. Thus, they kept it open during the day, once it had been opened in the morning. This practice promoted mosquito breeding, algal growth and contamination with organic matter. Sometimes this also encouraged small biological fauna contaminating stored water

Ineffective use of first flush systems

The first flush system is kind of a manually operated system. Therefore, somebody has to operate it correctly during the rain avoiding contaminated roof run-off entering into the tank and to enter the roof runoff after the first flush into the tank. But villagers aren’t so much interested in this procedure and they neglect this task. Therefore, the first flush will be stored in the storage tank.