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Rainwater harvesting system at BUET:

Introduction

Bangladesh University of Engineering and Technology (BUET) is the oldest institution for the study of Engineering and Architecture in Bangladesh. BUET initiated to install RWHS at its campus for reducing the water logging problem during monsoon. Auditorium and cafeteria rooftop are considered as catchment for harvesting rainwater under a piloting scheme. The initiative was supported by WaterAid. RAiN Forum provided technical support during design and implementation.

Catchment

Rooftop of Auditorium = 156 sqm

Rooftop of Cafeteria= 736 sqm

Components

Rainwater storage system

Rainwater recharge system

Rainwater harvesting potential

Total Cost: BDT. 4,02,666.00

Total RWH potential = 1540 m3 = 15,40,000 L

RWH potential for rooftop in cafeteria = 736 * 2.15 * 0.80 = 1272 m3 = 12,72,000 L

RWH potential for rooftop in auditorium = 156* 2.15 * 0.80 = 268 m3= 2,68,000 L

Design details

Size of siltation tank = 3.5ft * 3.5ft* 3.5ft

Size of filter chamber = 3.5ft * 3.5ft* 3.5ft

Size of storage tank = 2000 L (1000L capacity PVC Tank, two for each section)

Stored water will be used for toilet flushing purposes (in 4 toilets and 4 urinals)

Recharge well details

Two 6 “ dia PVC pipes were installed having same dimensions. After onsite soil investigation clay layer was found up to 20 ft. Therefore, borings were done one having depth of 50ft and another having 60ft. 20 ft long strainer were placed one at a depth of 30 ft and another at a depth of 20ft. Two flow meters have been attached with these two recharge pipe to investigate the amount of water recharging into ground water. Variation of strainer placement will also provide data on deviation on recharge amount of two different pits. Water table during monsoon is 94’-00”.

Size of de-silting chamber = 8ft * 5ft* 5ft

Size of percolation pit = 3ft * 4ft * 5ft

 

caffe roof 

Catchment

 

caffe toilet 

Rainwater Connection to Urinal

 

caffe pipe 

Rainwater Downpipe

 

caffe filter 

Recharge Wells

 

RWHS at Village Education Research Centre (VERC):

VERC is a national non-government organization who aims to work for women and children. VERC has introduced Rainwater Harvesting System (RWHS) in its head office premises for supplying water to training centre and head office. Presently ground water is being used as main water source. During dry season it becomes tough to extract ground water by using double jet pump because ground water is depleting day by day. The organization was looking for a sustainable source of water which can be an effective alternative of ground water source. After having the RWHS technology, it intends to install these systems in their premises. Now it is contributing to the main water source and also recharging the ground aquifer. The initiative was supported by WaterAid. RAiN Forum provided technical support during design and implementation.

Interventions:

Rainwater Storage System

Rainwater recharge System

Catchment:  Rooftop of 7storeyed building

Catchment area:  Rooftop area: 3600 sft = 335 m2

Filter tank

Rainwater Harvesting Potential:

RWH potential for rooftop = 335 * 2.15 * 0.85

= 610 m3 = 6, 10,000 L

Total Cost: BDT. 3,16,000.00

Design Details:

Size of siltation tank = 2ft 9 inch * 6ft 1 inch * 5ft

Size of filter chamber = 8ft 6 inch * 6ft 1 inch * 5ft

Size of storage tank = 20000 L (existing underground reservoir)

Total Cost of recharge well BDT =1,48,465.00 (One Lac Forty Eight Thousand Four Hundred Sixty Five only)

Recharge well details:

Two 6” dia PVC pipe installed having same dimension. First 70’-00”were identified as clay layer and then 30”-00” ft strainer was placed in sandy layer. Water table during monsoon was 42’-00”. Percolation pit has the dimension of 3ft* 4ft each. Adjacent to that percolation pit single siltation come storage pit for recharge well has been constructed having size of 4ft * 5ft.

Total Cost :

1. Cost of Filter and Siltation Chamber BDT 1,68,785.00( One Lac Sixty Eight Thousand Seven Hundred Eighty Five only)

2. Cost of recharge well BDT 1,48,465.00 (One Lac Forty Eight Thousand Four Hundred Sixty Five only

3. Total Cost of RWHS BDT 3,17,250.00 (One Lac Forty Eight Thousand Four Hundred Sixty Five only)

  caffe diagram

caffe filter plan

caffe filter02

 

Independent University Bangladesh (IUB)

Catchment: Rooftop

Catchment area

Rooftop area: 27592 sft = 2564 m2

Half roof-top: 1282 m2

Sector of using rainwater

Toilet flushing

Assumption:

Runoff coefficient for rooftop area: 0.85 (varies in between 0.8 – 0.9)

Runoff coefficient for paved area: 0.65 (varies in between 0.6 – 0.7)

Runoff coefficient for unpaved area: 0.35 (varies in between 0.3 – 0.4)

RWH from rooftop= 1282 m2 * 2.15 * 0.85= 2343m3 = 23, 43, 000 L