Executive Summary
What was this pilot project about?
This pilot project demonstrates the use of a modular infiltration ditch system for rainwater harvesting to effectively manage rainwater locally despite sealed surfaces. The system, installed at the pilot site of IIT/ISM University in Dhanbad, serves as an example of an underground rainwater reuse and storage option for urban locations in India. Unlike conventional harvesting systems, the system is not visible and does not require expensive land. Rainwater collected from roof areas is directed to an underground rainwater collection basin with infiltration capability to recharge groundwater and to protect surrounding areas from flooding.
Sedimentation shafts and control shafts and a water level allow for analogue system monitoring on-site (see Figure 1, Figure 2 and Figure 3). A solar-powered weather station (see Figure 4), added in April 2023, transferring data such as temperature, rainfall in mm, relative humidity %, and precipitation in mm, and a water level senso, allow for digital remote system monitoring. Overall aim of the pilot was to design the system for easy operation and monitoring by local operators, minimize breakdowns and maintenance requirements and allow for remote system control. Also, potential advantages of the piloted technology over conventional rain water harvesting systems commonly used in India were evaluated.
Figure 1. Location of the sedimentation shafts at the pilot site. Source: ODENTHAL (2023)
Figure 2. Sedimentation shaft in operation at the pilot site. Source: ODENTHAL (2023)
Figure 3. Control shaft at the pilot site. Source: ODENTHAL(2023)
Figure 4. Weather Station at the pilot site. Source: ODENTHAL (2023)
General project profile
System capacity: ~ 100m3/day
In steady-state operation since 06/2022
Piloted technological system
Input: Rainwater (rooftops)
Output: 10-20 m3 rainwater per hour
Flow scheme: Solid collector + storage modules + gravel layer (infiltration ditch)
The system is also equipped with a weather station for remote system monitoring
| Use of outputs/products: | This pilot system intends to offer an option for infiltrating purified rainwater for groundwater recharge despite sealed surfaces. In order to purify the rainwater appropriately, the rainwater is cleaned by four cleaning shafts before it flows into the infiltration system and passes through a geotextile fleece, sand, and gravel layers prior to reaching the groundwater. |
Location and conditions
This pilot project is located at the campus of Indian Institute of Technology Dhanbad (see Figure 5) next to a newly built 13-story hostel for approximately 2000 students near to Sapphire Hostel. The total population of IIT(ISM) Dhanbad campus is approximately 10.000 inhabitants including students, faculty, and staff residing on the campus.
Figure 5. Location of Rainwater Harvesting Pilot in Dhanbad. Source: ODENTHAL (2023)
Dhanbad is the coal capital of India and is the second most populous city in the state of Jharkhand. It features climate that is transitional between a humid subtropical climate and a tropical wet and dry climate. Summer starts from last week of March and ends in mid-June. Peak temperature in summer can reach 48 °C. In winter, the minimum temperature remains around 10 °C with a maximum of 22 °C. Dhanbad also receives heavy rainfall (around 1.200-1.400 mm per year and m2 with July, August September being the rainy season.
Reintegrate rainwater, prevent flooding, keep surface areas open for other uses
Since IIT(ISM) campus mostly relies on groundwater for various domestic water needs, the goal of the pilot system in Dhanbad was to reintegrate rainwater from the roof of a recently constructed dormitory into the natural water cycle while ensuring its usability without prior contamination. A further target was to significantly minimize the rainwater masses on the site during the rainy season and thus to have no standing rainwater around the building. All hostels previously built on the campus are having roof top rain water harvesting systems (Conventional Type). This pilot was intended to serve as an experimental site to allow evaluating the advantages of an underground modular rainwater harvesting system over “conventional” ones. Large parts of the roof area of a newly built hostel were supposed to be connected to a modular underground rainwater collection system (see Figure 6) so the drainage of rainwater on the property is no longer perceived as a disruption, as the water masses are collected underground and there is no flooding on the property. Further arguments for this type of system were its high load-bearing capacity. Overlying surface areas can be used for various purposes such as roads for vehicles up to 40 tonnes, courtyards, vegetation areas or sports areas.
The rain water harvesting system has the following dimensions: 24.09 m x 6.49 m x 0.66 m (length x width x height). The total volume with the hard plastic parts is 103,19 m3. The filling volume of the rain water system is made for 97,32 m3. The gravel bed underneath the RWH System has a pore volume of approx. 20-25 m3. The weather station and its sensors are located centrally above the infiltration trench.
Figure 6. View from inside the underground modular infiltration ditch system. Source: ODENTHAL (2023)
Project milestones
Below are the major steps we took for implementing this pilot project:
- Technical baseline study and soil survey: general evaluation of local conditions and geological assessment of sub-soil (by borehole drilling) to evaluate soil conditions + rapid soil testing on-site to specify infiltration characteristics
- Pilot design (EU): preliminary design followed by more detailed design and drawings following site visits of KRETA
- Purchase of equipment: the particular modular components for this system were not available in India and were purchased in Germany. Additional materials such as filter fleeces, various gravels and sands were available in India and purchased locally.
- Shipment of rainwater harvesting module: materials were shipped by freight from Hamburg port to Kolkata port in October-December 2021 and then transported to Dhanbad. The administrative process necessary for shipment and customs is quite laborious and has to be planned for accordingly: for example considering the list of documents that was necessary: Original Bill of Loading, Original Commercial Invoice, Original Packing List and Delivery Note, PO copy, DSIR certificate, Letter in terms of Notification No 051/96-Cus, Insurance premium (all goods are insured until handover via the manufacturer), Technical Write-up, Confirmation of participation in the EU H2020 research project PAVITR, Export accompanying document, Certificate of Origin.
- Construction and installation work (local infrastructure and pilot station): after preparatory work like excavation work for the drainage pit, the layer bedding was levelled. This step was followed by building up sand and gravel layers separated by a fleece layer to optimise local infiltration characteristics. On top of this, the geotextile was laid. Then the rainwater harvesting modules, connectors between the modules as well as the inspection and cleaning shafts and the piping were installed in April 2022. The backfilling work followed in May 2022. During the construction period, the system was monitored by PAVITRs local project members at IIT ISM. In January 2023, around 1300 m2 of the 2400 m2 roof area was connected to the system.
- Start-up phase
- On-going monitoring: since April 2023 remote monitoring of system through the weather station and water level sensor
As more general remarks or learnings from this implementation process, it can be noted that in order for the system to be installed quickly, the well-organising of all materials required for installation is key for a smooth installation process
Who was involved
At the time of the publication of this case study, the respective information was not specified by the authors.
Set-up of operation and maintenance phase
The system is designed so day-to-day O&M requirements are kept at a minimum. One important aspect for that is to limit potential blockages: coarse material transported with the rainwater is collected in a series of four sedimentation shafts before it enters the collection modules. The dirt settles in the shafts and does not enter the modules. With regular checking (and cleaning if necessary) of the sedimentation shafts and cleaning of the roof surfaces the rainwater is collected from (twice a year minimum), the collection modules can operate maintenance-free for up to 10 years. For the 10-year inspection, a camera robot is placed in the system through the control shaft, drives along the individual corridors and checks the collection modules for signs of clogging or blockages. For this task, and for back-flushing in case the entire system requires a general cleaning, a specialised third-party company is assigned.
In the first monsoon period in 2022, the system was already connected to a part of the roof surfaces, but there was still no digital monitoring equipment installed. In this period, the system was monitored on-site through regular visits by IIT ISM project staff. Since the installation of a weather station and a water level sensor in April 2023, monitoring can also be carried out remotely since weather and water-level data are recorded hourly and stored online. The data are accessed online at any time and updated every 5 minutes.
During the rainy season, on-site monitoring must be carried out more frequently than in drier periods, to check the inspection- and sedimentation shafts must be checked for clogging and cleanliness – since more material is transported towards the system. The actual monitoring routine during the rainy season depends on the rainfall pattern and needs to be adapted accordingly.
Operational experience and performance
A first inspection, respectively maintenance activity (see Figure 7 and Figure 8), in January 2023 but also the remote monitoring of the system (starting in January 2023) show that the infiltration system works efficiently and is completely function. The system is constantly recharging groundwater with new rainwater that is filtered and infiltrated to the groundwater. Also, after the first monsoon period in 2022, the system did not show any clogging or contamination that could negatively affect the function of the system in the future. The four cleaning/sedimentation chambers have succeeded to collect a lot of mud and small and large particles of dirt and deposited them in the mud flap, thus safeguarding the drainage system from clogging.
Figure 7. Maintenance work at the pilot site. Source: ODENTHAL (2023)
Figure 8. Maintenance work at the pilot site. Source: ODENTHAL (2023)
Nevertheless, one observation was that the roof surfaces, on which the rainwater is collected and channelled into the underground rainwater system via downpipes, were in a very poor condition. Construction waste, stones, pieces of plastic and other small parts were scattered all over the roof surface (see Figure 9). This can clog the system and contaminate the filter fleece. The system has to be maintained more often than usual due to the incoming dirt. This results in unnecessary additional costs and may lead to blockages in the pipes. This can be avoided very easily on site by removing dirt from the roof surfaces and keeping them clean.
Figure 9. Dirt on the roof surface areas at the pilot site. Source: ODENTHAL (2023)
Also, there were technical difficulties with the weather station on site: the location of the weather station was not optimal, and the water level sensor and the rainfall display were faulty. There were discrepancies in the data of the rain sensor and resulting in lacking data for the amount of precipitation in the months from March to June 2023. A repair and optimization of the location of the weather station was planned for Q1 2024.