Group- B

Diksha Shrestha

Hemanta Raj Shrestha

Inashree Piya

Jeny Shrestha

Kishor Banstatoki

Madhuri Maheshwori Shrestha

Harvesting Rainwater

Introduction

• Rainwater harvesting is a technique used for collecting, storing, and using rainwater for landscape irrigation and other uses.

• It is the process of augmenting the natural filtration of rainwater in to the underground formation by some artificial methods.

• The rainwater is collected from various hard surfaces such as roof tops and/or other types of manmade above ground hard surfaces.

Why harvest rainwater?

• To stop ground water decline• To conserve surface water runoff

during monsoon• To reduce soil erosion• To inculcate a culture of water

conservation

• Easy to maintain• Meet the increasing demand of

water• To supplement domestic water

requirement during summer and long dry time

Significance

Significance Cont...

• Large reduction in utilities bill• Reduce demand of ground water• Reduction of soil erosion and landslides • Can be use for many purpose

Disadvantages

• Limited and uncertain local rainfall• Requires some technical skills to install and provide

regular maintenance• If not installed correctly, may attract mosquitoes• Certain roof types may leak chemicals, pesticides,

and other pollutants into the water that can harm the plants

Rainwater Harvesting Capacity Centre(RHCC)

• Conscious collection and storage of rainwater to cater to demands of water, for drinking, domestic purpose & irrigation is termed as Rainwater Harvesting.

• RHCC promotes the technology of Rainwater Harvesting in Nepal.

• RHCC operates under Biogas Sector Partnership Nepal (BSP-Nepal).

Dos and DON’Ts

• Roof or terraces used for harvesting should be clean, free from dust, etc.

• Do not store chemicals, rusting iron, manure or detergent on the roof.

• Provision of first rain separator should be made to flush off first rains.

• Filter media should be cleaned before every monsoon season.

Do’s and Dont’s cont...

• During rainy season, the whole system (roof catchment, pipes, screens, first flush, filters, tanks) should be checked before and after each rain and preferably cleaned after every dry period exceeding a month.

• At the end of the dry season and just before the first shower of rain is anticipated, the storage tank should be scrubbed and flushed off all sediments.

Suggestions

• Kathmandu Upatyaka Khanepali Limited can only fulfill 33% of valleys demand.

• Rainwater harvesting can save upto 130,000 liters of water per year.

Sizing the system

• Storage tank requirement will be determined by a number of interrelated factors:1. Local rainfall data and weather patterns

2. Size of roof (or other) collection area

3. Runoff coefficient (this varies between 0.5 and0.9 depending on the roof material and slope)

4. User numbers and consumption rates

Method for sizing RWH system components

• Method1: Demand size Approach– Method based on consumption rates and occupancy of the

building– Assumes sufficient rainfall and catchment area– For example:

Consumption per capita per day, C=20 ltrs

Number of people per household, n=6

Longest average dry period= 25 days

Daily consumption= C x n= 120 ltrs

Storage requirment, T= 120 x 25= 3000 ltrs

Methods cont...

• Method 2: Supply Side Approach– Used in low rainfall areas or areas where rainfall is of uneven

distribution– A common scenario in developing countries where monsoon or single

wet season climates prevail.– Example taken from a system built at a medical dispensary in the

village of Ruganzu, Tanzania– Lpcd= litres per capita per day

Demand:Number of staff:6Staff Consumption : 25 lpcdPatients:30Patients consumption:10 lpcdTotal daily demand:450 ltrs

Supply:Roof area: 190 sq.meterRunoff Coefficient= 0.9Average Annual Rainfall:1056 mm per yearDaily available water(assuming all is collected)=(190x1056x 0.9)/365=494.7 ltrs