Day 02::Thematic Session 03

Day 02::Thematic Session 03

Rainwater harvesting for promoting artificial recharge to encounter the loss of waterbodies due to encroachment.

Bangladesh Convention on Rainwater Harvesting
Hotel Ruposhi Bangla, Dhaka,
15 to 17 June 2012

Introduction

This session’s theme was ‘Rainwater Harvesting for Promoting Artificial Recharge to Encounter the Loss of Water bodies Due to Encroachment’. Four presentations were made by Ms. Anika Tabassum, Ms Shahnoor Hasan, Mr Mizanur Rahman and Mr Roshan Raj Shrestha.

The session was moderated by Ms. Tanuja Ariyananda, Executive Director of the Sri Lanka Rainwater Harvesting Forum.

Paper 1: Potential of Rainwater Harvesting to Address Water Logging Problem: A Case Study At Senpara Porbota, Mirpur, Dhaka by Ms. Anika Tabassum

The presenter defined Rainwater Harvesting (RWH) as a process of collecting, conveying and storing water from rainfall in an area – for beneficial use through storage in tanks, reservoirs, or underground storage.

The study was conducted in the residential area of Senpara Parbata in Mirpur, Dhaka, Bangladesh which is a populous area of Dhaka city. Here, roof based RWH systems were studied. The reason for using RWH for reducing water logging is because it is economic, easy to install, easy to operate and maintain and environment friendly. RWH methodologies include the utilization of:

– Roof Rain Water Harvesting

– Land based Rain Water Harvesting

– Watershed based Rain Water harvesting

For Urban & Industrial Environment:

– Roof & Land based RWH

– Public, Private, Office & Industrial buildings

– Pavements, Lawns, Gardens & other open spaces

Water logging arises due to 3 major reasons:

 Physical

– Clogged and inadequate drainage system

– Encroachment of the city canals/water bodies

– Narrow water pipes installed by WASA unable to drain out huge amount of water

 Manmade

– Involvement of multiple organizations

– Poor maintenance of drainage infrastructures

– Lack of coordination among WASA, DCC and RAJUK

– Lack of manpower for cleaning purpose

 Climate Change related

– Shift in the baseline and accentuation of extreme rainfall

– Variation in days with rainfall and days without rainfall

Recommendations:

Clearly, if people are made aware of the benefits of RWH more and more residents will be eager to invest in such beneficial modes of water collection, especially since the region investigated is regularly effected by water shortage. Massive awareness campaigns through media, training real users, strict legislation, incentives form the government and making RWH mandatory are some of the suggestions were given by the presenter.

Paper 2: Role of Educational Institutions in Promoting Rainwater Harvesting System: A Case Study on Independent University, Bangladesh by Ms Shahnoor Hasan

Ms. Hasan began with an overview of the water crisis that affects Bangladesh annually. The supply-demand gap of water is so wide that the measures taken are not much effective. The root of the crisis lies in the unavailability of both surface and groundwater. The surface water from polluted rivers is inadequate and in some cases beyond treatment.

Since the residents of Dhaka city have become captive to the natural and manmade hazards, rainwater harvesting system (RHS) has been recognized as an alternative and effective solution. This method could supply more than 15% of Dhaka’s thirst with an annual average rainfall of around 2,150 mm. Water collected can be stored for four to five months without bacterial contamination, thus possibly reducing the incidence of diarrhea. Although The Ministry of Housing & Public Works and Rajdhani Unnayan Kartripakkha have proposed rainwater harvesting mandatory for all new houses and also stipulated that buildings with a minimum rooftop area of 300 m2 must have the provision for harvesting rain water, there is a lack of knowledge and awareness from the users’ end.

IUB as the source of RWH:

In this context, various educational institutions can come forward with their collective force of teachers and students, and that is what IUB has tried to do. The paper focuses on the key role the educational institutions can play in promoting RHS. The students who come from various strata of the society can play a vital role in spreading this concept. By addressing the issue with a case study of Independent University, Bangladesh (IUB) an example is provided so that other institutions can emulate IUB in doing the same. The system designed at IUB with the assistance from Water Aid, Bangladesh has both the storage and recharge facilities. The total annual potential is approximately of 1.21 million liters.

Graphical presentations of peak months for the availability of rainwater from May to October, a deficiency in rainwater was shown from January to April and then once again from late October to December. However, a large portion of the water demand may be fulfilled by stored rainwater. She also portrayed the detailed diagrams, pictures and graphs depicting the RHS of IUB where rain water from the catchment area on the rooftop goes into the de-silting tank, then to the filtration chamber and then to the storage tank.

The financial benefits are considerable:

– Each year approximately BDT 5,202 as DWASA bill and BDT 24,000 as the cost of electricity consumption to extract water would be saved.

– In addition, approximately a minimum amount of BDT 5,000 would be saved annually as the maintenance cost that arises from runoff of rainfall.

– A total cost of BDT 34,202 would be saved per annum

– The total cost has been BDT 4,16,168; considering the above factors, the payback of the designed system would be achieved by 12.16 years.

Concluding remarks:

In her concluding remarks, Ms. Hasan expressed her satisfaction with the success of the RHS of IUB and her expectation that various other educational institutions would come forward to follow the example set by Water Aid and IUB. She also supported the need of better surface water management practices.

Questions from participants addressed to Ms Shahnoor Hasan, and Ms Anika Tabassum her replies:

1. How can such RHS be installed in a small scale, especially in apartments since urbanization is rapidly increasing?

Answer: The proposed building code of Bangladesh includes a provision to install RWH systems. They must be installed if the building has a roof top surface area of 300 m2. The Rainwater Forum may also be consulted. There is a lack of trained masons who can help construct such systems. So, training them should also be focused on to popularize this concept.

The presenter also added that the RHS is an easy instrument to install, all paved roof tops may collect water through pipes and the water may be used for washing and cooking purposes. The underground and overhead tanks may be designed to collect water. In case of existing structures, the overhead tanks may be used.

2. With a cost of around BDT 4 Lacs for installing the RHS in IUB, the annual repayment is around BDT 30,000. How can institutes manage this money? Do any organizations provide any loans/schemes which may assist such institutes?

Ms Shahnoor: Water Aid has assisted IUB in its initiative to install RHS. The organizations which arranged this conference-CSE, IWM, Rainwater Forum and Water Aid- may all be of some assistance in such projects.

3. In what ways may the people who were present in this conference spread the concept of RWH?

Ms Shahnoor: The faculty of IUB has taken the initiative to educate the students and create awareness about this concept among them. Since the students come from various regions and strata of the society, they may spread the message effectively. Similarly, simple graphical presentations, awareness campaigns and such conferences will help to spread the importance and effectiveness of RHS.

Moderator Ms. Tanuja Ariyananda wrapped up the first part of the session with some comments:

• Since the monsoon weather is about to begin, these concepts have been publicized at the ideal time and therefore must be unitized.

• RWH is an important tool to combat droughts, floods and climate change

• It is an efficient and affordable method which can drastically reduce delivery and treatment costs.

• Creating of this method is of utmost importance

• More pilot studies must be conducted to strengthen the effectiveness of RWH

• People must be repeatedly made aware and decision makers must repeatedly suggest this method.

• IUB’s example must be showcased to other institutes. Educational facilities are a good place to promote this concept since the younger generations must take this concept forward

• RWH methodologies must be introduced into the mainstream and the school/college curriculum.

• Training masons is also very important.

• An information centre, with the Rain Forum perhaps, is necessary so that people eager to utilize these methods may have immediate access to relevant information and advice.

Paper 3: Artificial Recharge to Dhaka Aquifer from Rainwater is Inevitable for Aquifer Environment and Water Supply by Mr Mizanur Rahman

The presentation began with an overview of the current situation of the aquifer environment of Dhaka. 13% of DWASA production comes from surface water and 87% comes from groundwater. The declining supply of water has led to the initiation of a project by IWM to collect water from Singair. Mr Rahman shows by graph that long term groundwater decline trend in Dhaka is visible from records the depth of the groundwater from 1969 to 2007.

Possible sources of Aquifer Contamination:

– Accumulated liquid waste in pit

– Waste from dyeing industries

– Municipal waste at Maghbazar

– Industrial waste discharged

– Hanging latrine

Four recharge options are available for mitigating the groundwater mining situation:

– Vertical recharge from surface runoff

– Interaction recharge from surrounding river flow

– Horizontal recharge from distant sub-surface inflow

– Artificial recharge from harvested rainwater

Objectives of Artificial Recharge to Aquifer:

– Restore declined GW levels and mitigate aquifer mining.

– Ensure dependable yield of production wells

– Improved water quality through dilution of harmful chemicals

– Control force recharge condition to avoid polluted river water intrusion in to aquifer

– Reduction of pumping cost especially where groundwater level is depleting

– Utilization of clean rain water, which otherwise drains off causing water logging

The Sequence of the pilot study in artificial recharge to Dhaka aquifer followed these steps:

– Field survey and data acquisition

– Selection of the pilot study sites and building

– Quantification of hydrogeological variables

– Exploratory drilling, sediment sampling and analyses

– Outline design of rain water harvesting system

– Construction of artificial recharge structures

– Collection of rainwater and GW samples and analyses

– Determination of hydrostatic pressure required for gravity inflow of recharge water

Necessary physical works carried out at site included:

– Necessary development of roof top

– Rainwater collection network construction

– Fixing of rain gauge on roof top

– Recharge / injection well construction

– Recharge pit construction

Concluding remarks:

If 60 % of the rainfall from roof top can be harvested, more than 200 MLD water can made available for use. Considering 50% collection, annually 14,510 ML will be available for storage in underground reservoir and ready use of 80 MLPD during the 6 monsoon months.

Mr Rahman concluded his presentation with the following remarks:

– Excessive pumping in Dhaka City is endangering the aquifer environment.

– Threat arises because of imbalance in groundwater recharge and abstraction.

– Groundwater mining situation should be avoided.

– Available safe yield in upper aquifer is 604 Mm3/year.

– Available storage volume in deeper aquifer is 139 Mm3/year

– Due to force recharge aquifer is being contaminated from river water.

– Rainwater is acceptable for artificial recharge after 10 minutes shower.

– DWASA abandoned wells is not a good option for using as injection well.

– If 60 % of the total rainfall from roof top can be recharged, more than 200 mld water will be available.

– RAJUK has proposed 10 different zones where 10 different studies will be conducted by IWM to formulate recommendations and prototype designs and costs.

– Online services will also be provided by IWM for designing and suggestions regarding recharge pit/well.

Paper 4: Local Initiatives for Rainwater Harvesting & Ground Water Recharge in Kathmandu by Mr Roshan Raj Shrestha, Ph.D

The presentation is based on the situation of the water crisis in Nepal and methods that are applied to tackle it. Two case studies were given, firstly the initiatives taken by the Nepalese to regenerate the traditional water sources eg, ponds and dug wells and the second was the presenter’s own home which is an ‘eco-home’.

Mr Roshan urges, better management of rainwater harvesting is now the only hope to mitigate the current water crisis and revive traditional water management system and reveals that the potential of RWH in Kathmandu Valley is immense as the following statistics suggest:

– The average rainfall in the Kathmandu Valley is estimated around 1900 mm: more than twice the world average.

– Approximately 1.2 billion m3/year or 3353 MLD of rainwater falls in the 640 sq.km Valley.

– This is about 12 times the present water demand (102 million m3/year)

– If only 10% of the Kathmandu Valley area is to be utilized for rainwater harvesting, 128 million cubic meters per/ year could be recharged

Realization of the importance of rainwater has led to the nationwide project- Local Initiative for Conservation of Traditional Water Sources through Rainwater Harvesting & Ground Water Recharge, with the collaboration of several national and international organizations, universities and MNCs

The project had 4 main objectives:

– Establish RWH system in traditional ponds to demonstrate recharge mechanism and augment the ground water table.

– Establish community level recharge wells and pits to demonstrate recharge mechanism and augment the ground water table.

– Promote RWH techniques through demonstration and awareness building

– Conduct a detailed research on the potential areas of groundwater recharge and prepare detailed design of the recharge pits suitable for the different locations

Concluding remarks:

Mr. Shrestha concluded his presentation with the following remarks:

• Ponds are the critical component of the water supply system which need to be conserved and used for recharging ground water

• Shallow aquifer should be used as an underground water reservoir to store rainwater

• Rainwater harvesting at household must be practiced by the citizen where ever it is feasible

• Recycling of grey water must be integrated with rainwater harvesting for sustainable water

• Role of Local authorities is crucial to mobilize and encourage in RWH

Questions from participants addressed to Mizanur Rahman and his answers:

1. Nepal is using easily available methods to utilize rainwater, then why isn’t such methods being applied in Bangladesh?

Answer: Other nations are using RWH from ancient times, whereas such methods have just begun in Bangladesh, therefore it will take some time to become a common phenomenon.

2. Are there any guidelines in NBC code for civil engineers and architects?

Answer: IWM sat with RAJUK, WASA and a draft was made regarding this matter. SRO and government approval is expected soon. It is clearly stated by RAJUK that new buildings with rooftop of 300 m2 must use RWH techniques.

3. Why isn’t the system of destroying the ground water being addressed by industrialist and effluent treatment plants?

Answer: Industrialists used to throw waste into rivers, nowadays, due to awareness programs, the waste is thrown into the groundwater source which is much more dangerous.

4. Is there any plan to use the rainwater directly from the groundwater?

Answer: The thick clay layer above the groundwater prevents the direct collection of rainwater as the water at that stage may be harmful.

5. The upper layer of Singair is fully affected by arsenic. Is the survey conducted by IWM a full survey or is it just a plan?

Answer: The survey was a detailed study of Singair and Savar. Two certain areas of Singair aren’t affected by arsenic, several tests have been conducted and no variation has been found in the water chemistry.

Questions addressed to Mr. Rosan Raj Shrestha and his answers:

1. Several initiatives have been taken in rural Bangladesh to introduce RWH, however they failed at some stages. What are his suggestions to reap the benefits of this concept? How could this initiative be used practically in Bangladesh?

Answer: Initiatives can be very simple with very simple instruments. Recharge of shallow aquifer is easy because recharge of deep layer requires bypass of clay layer. Yet shallow layer may be utilized just before the clay layer is reached.

2. How is solar energy used to disinfect rainwater?

Answer: Water is filtered to remove sediments and then is put in transparent plastic bottles. These bottles are kept in the sunlight for up to 7 hours. This will purify the water.

Moderator Ms. Tanuja Ariyananda wrapped up the session with the following comments:

Mizanur Rahman addressed the deficit of water which is rampant in Bangladesh and technical initiatives taken by IWM to overcome the problem. The huge problem caused by excessive pumping and the potential of RWH has also been explored. Ground water recharging and which levels should be recharged and the geological situation of the areas with water content problem have also been explored.

Dr. Shreshtha showed the traditional RWH systems of Nepal and how they have been revived. By showing the initiatives that he has taken in his own house he has proved that such concepts are actually quite practical.