Requirements for Rainwater Harvesting Pits in Residential Complexes
Rainwater harvesting is an essential component of sustainable building design and can help reduce water consumption and preserve water resources. The National Building Code of India (NBC) has provided guidelines for rainwater harvesting systems in residential complexes to ensure that they are designed and installed correctly. In this article, we will discuss the requirements for rainwater harvesting pits on residential complexes as per the NBC.
Requirements for Rainwater Harvesting Pits
According to the NBC, the following requirements should be met for rainwater harvesting pits in residential complexes:
- Size of Pits: The size of the rainwater harvesting pits should be based on the rooftop area from which rainwater is being collected. The minimum size of the pit should be 1 cubic meter for every 20 square meters of rooftop area.
- Location of Pits: The rainwater harvesting pits should be located at a distance of at least 3 meters from any building or structure. The pit should be located in an area where it will receive maximum rainfall and should be easily accessible for maintenance.
- Depth of Pits: The depth of the rainwater harvesting pits should be at least 1.5 meters to ensure that the harvested water remains cool and does not become stagnant.
- Inlet and Outlet Arrangements: The inlet and outlet arrangements for the rainwater harvesting pit should be designed to ensure that the harvested water is of good quality and can be easily withdrawn for reuse. The inlet should be fitted with a fine mesh to prevent debris from entering the pit, and the outlet should be fitted with a filter to remove any sediment or contaminants.
- Overflow Arrangements: The rainwater harvesting pit should have an overflow arrangement to ensure that excess water is safely discharged. The overflow arrangement should be designed to prevent erosion and should discharge water away from the building or structure.
- Maintenance: Regular maintenance of the rainwater harvesting pit is essential to ensure that it functions effectively. The pit should be inspected and cleaned at least twice a year, and any sediment or debris should be removed.
sample calculation table for determining the size of the rainwater harvesting pit based on the rooftop area of a residential complex:
| Parameter | Calculation | Result |
|---|---|---|
| Rooftop Area | 1000 sq. m. | |
| Size of Pit | Rooftop Area / 20 | 50 cubic meters |
| Pit Depth | 1.5 meters | |
| Inlet and Outlet Arrangement | As per design | |
| Overflow Arrangement | As per design | |
| Maintenance | Regular cleaning and inspection |
In this table, the rooftop area of the residential complex is assumed to be 1000 sq. m. Based on this, the size of the rainwater harvesting pit is calculated to be 50 cubic meters, which is equivalent to 1 cubic meter for every 20 square meters of rooftop area. The depth of the pit is assumed to be 1.5 meters, and the inlet and outlet arrangements, overflow arrangement, and maintenance are as per the design specifications.
Requirement as per LEED
Peak rainfall calculation is an important aspect of sizing a rainwater harvesting system for meeting LEED compliance. By calculating the peak rainfall, the rainwater harvesting system can be designed to capture and store the maximum amount of rainwater, which can be used for non-potable purposes such as irrigation, toilet flushing, and cooling tower makeup water. In this article, we will discuss how to calculate peak rainfall for sizing a rainwater harvesting system for meeting LEED compliance.
Calculation of Peak Rainfall
The following steps can be followed to calculate the peak rainfall for sizing a rainwater harvesting system:
- Determine the catchment area: The catchment area is the surface area from which rainwater is collected. It can be calculated by measuring the surface area of the roof or any other surface from which rainwater is collected.
- Determine the rainfall intensity: The rainfall intensity is the amount of rainfall that occurs during a specific time period. It is measured in millimeters per hour and can be obtained from local weather data or rain gauge measurements. In India, the National Building Code (NBC) recommends a rainfall intensity of 100 mm/hour for the design of rainwater harvesting systems.
- Calculate the peak rainfall: The peak rainfall is the maximum amount of rainfall that can be expected during a specific time period. It is calculated by multiplying the catchment area by the rainfall intensity. For example, if the catchment area is 500 square meters and the rainfall intensity is 100 mm/hour, the peak rainfall can be calculated as follows:
Peak Rainfall = Catchment Area x Rainfall Intensity Peak Rainfall = 500 sq. m x 100 mm/hour Peak Rainfall = 50,000 liters/hour
This means that during the peak rainfall, the rainwater harvesting system should be able to capture and store 50,000 liters of rainwater per hour.
Sizing the Rainwater Harvesting System
Once the peak rainfall has been calculated, the rainwater harvesting system can be sized accordingly. The size of the storage tank should be able to hold the maximum amount of rainwater that can be collected during the peak rainfall period. The system should also be designed to prevent overflow and ensure that the harvested rainwater is of good quality and suitable for reuse.
Peak rainfall calculation is an important aspect of sizing a rainwater harvesting system for meeting LEED compliance. By calculating the peak rainfall, the rainwater harvesting system can be designed to capture and store the maximum amount of rainwater, which can be used for non-potable purposes. By complying with LEED requirements for rainwater harvesting, buildings can reduce their water consumption and contribute to a more sustainable future.
sample calculation table for determining the peak rainfall and sizing the rainwater harvesting system for a building with a catchment area of 800 square meters:
| Parameter | Calculation | Result |
|---|---|---|
| Catchment Area | 800 sq. m. | |
| Rainfall Intensity | 100 mm/hour | |
| Peak Rainfall | Catchment Area x Rainfall Intensity | 80,000 liters/hour |
| Storage Tank Size | Peak Rainfall x Storage Time | 160,000 liters |
In this table, the catchment area of the building is assumed to be 800 square meters, and the rainfall intensity is assumed to be 100 mm/hour, as per the NBC guidelines. Based on these values, the peak rainfall is calculated to be 80,000 liters/hour, which is the maximum amount of rainwater that can be collected during the peak rainfall period. The storage tank size is calculated by multiplying the peak rainfall by the storage time, which is the time period for which the stored rainwater will be used. For example, if the storage time is 2 days, the storage tank size should be 160,000 liters, which is equivalent to 80,000 liters/hour x 2 days
Rainwater harvesting pits are an essential component of sustainable building design and can help reduce water consumption and preserve water resources. The NBC has provided guidelines for rainwater harvesting systems in residential complexes to ensure that they are designed and installed correctly. By complying with these guidelines and regularly maintaining the rainwater harvesting pit, residential complexes can reduce their water consumption and contribute to a more sustainable future.