DELHI:EROS TIMES: The Indian Institute of Technology (IIT) Delhi on Wednesday presented its report on the causes of water-logging and flooding in Delhi to the Chief Minister Arvind Kejriwal in presence of concerned departments.
The report on storm water drainage infrastructure has prepared by the Department of Civil Engineering, IIT Delhi, had been commissioned by the Department of Irrigation and Flood Control. The report identifies the reasons behind clogging of specific sewers and drains.
The Chief Minister has directed the concerned departments to take concrete steps for the implementation of the report, which mentions in detail the specific reasons for water-logging and flooding during Monsoon season.
The meeting was attended by the senior officials of Irrigation & Flood Control, PWD, DUSIB, DDA, NDMC and DSIIDC.
Last Drainage Master Plan for Delhi was prepared in the year 1976, when the population of Delhi was 60 lakh. Population of Delhi as per Census 2011 stands at 167 lakh (1.67 crore) and the projected population as per projection in Master Plan Delhi 2021 is 250 lakh (2.5 crore). Present area urbanized in Delhi 750 sq. Kms and the likely area to be urbanized as per MPD-2021 is 920 sq. Kms.
To alleviate the flooding conditions in various parts of the city, the stormwater infrastructure has to be made efficient. So, it is pertinent to apply corrective measures to the faulty drainage infrastructure, and introduce low cost flood preventing measures such as water bodies rejuvenation, rainwater harvesting using parks and low impact Development options. Further, the solid waste and the sewage has be managed in such a way that they do not interfere with the stormwater drainage, the report notes.
The report states that Delhi has three major drainage basins, namely, Najafgarh, Barapullah and Trans-Yamuna basins.
TRANS YAMUNA BASIN :
Major drainage problems in the region :
rapid unplanned urbanization, shallow groundwater level and low elevation have resulted in frequent flooding problems in this region.
The major problems are as follows:
Shallow Ground Water table: Majority of areas lying in the western side face frequent water logging problems, primarily due to shallow groundwater levels during pre and postmonsoon periods.
Reversal of Flow Direction: The region is protected from frequent flooding in river Yamuna by providing two marginal bunds. This also prevents any direct outfall into the river. Relief Drain is the only drain which is having the outfall in the river. Majority of drains flow from west to east (from the Yamuna River to the eastern side of the basin) against the natural flow direction. The water from the North Eastern basin gets collected into the G.T. Road drain which carries it across the region.
Major drainage problems in the region :
As mentioned before, rapid unplanned urbanization, shallow groundwater level, low to medium elevation have resulted in frequent flooding problems in this region. The major problems are highlighted below.
Increasing paved surface, reducing water percolation and increasing runoff.
Reversal of flow direction and inadequate/failure in pumping:
The region is protected by a check dam in the Mehrauli area to prevent surface runoff coming from Haryana state and also to prevent water logging in the area. Chirag Delhi drain is the longest drain in the basin which carries all the runoff as well as sewage from the south district part of the basin and outfalls into Barapullah drain.
Often the construction debris in the new drains is not cleared, garbage is dumped on the roadside drains. No segregation between sewerage and storm water infrastructure. Low lying areas experience acute drainage congestion.
Encroachment by covering the drain and using the space for parking (as is the case at Khanpur chowk, where Chirag Delhi drain was covered and now the space is used for parking).
Major drainage problems in the region :
The water logging and drainage problem in the Najafgarh basin can be generally categorised as follows:
Drainage Congestion: On account of depressions at numerous places in the basin, the storm water from the nearby areas collect during the rainy season in these depressions.
Drains carrying storm water from outside Delhi: Drains (such as Najafgarh and Mungeshpur) which have their origin in the other states and carry considerable discharges into Delhi.
Failure in Pumping: Pumps have been installed at various locations by the government to pump out the storm water into the Najafgarh drain.
The failure of these pumps leads to drainage congestion in these areas. In addition, constant usage of mobile pumps to pump out the surplus amount of water into nearby drains, whenever required, affects the capacity of the drain and causes flooding in the downstream areas.
MAJOR RECOMMENDATIONS TO SOLVE THE PROBLEM :
No encroachments on storm drains
Storm drains should be treated as key public assets and no encroachment should be allowed. Any encroachment of the drain should be immediately removed and reported back. Department managing the storm drain should be made responsible for keeping drain encroachment –free. Special drives to remove encroachments from the storm drains should be taken up.
No sewage in storm drains
No natural or artificial storm drain should be allowed to carry any sewage. Only treated sewage of acceptable quality as per CPWD norms should be allowed in storm drains.
All drains that are entering into NCT of Delhi(from Haryana, U.P., etc.) should be only carrying storm water and treated sewage of acceptable quality as per CPCB norms.
Current practice of DJB of puncturing sewer lines and draining sewage into storm drain in the event of blockage should be stopped. DJB should resort to using latest mechanisms such as supper suckers for de-clogging the sewer lines.
No sewage should be allowed to enter the storm drains even from unauthorized colonies; interceptor sewers should be set-up wherever required by DJB to trap the sewage coming out of such colonies and take it to the nearest sewer line or STP.
No Solid Waste or C & D waste be allowed into storm drains
No silt from the road (before or after road sweeping- manual or otherwise) be allowed to be dumped into bell-mouths/drains. Road sweeping process should be completely overhauled. Weight/volume of silt received after street sweeping should be recorded. Segments of road from where more silt is being received should be reviewed and reason of the same ascertained. If need be, possible afforestation exercise should be taken up to reduce silt on the road segment.
No solid waste should be allowed to be dumped into storm drains.
Construction & Demolition (C & D) waste should not be allowed to be dumped in storm drains or depressions. Amount of waste likely to be generated from a construction or demolition site should be assessed by the contractor in advance (along with the permission to construct/modify house). C & D waste should be lifted by government appointed contractors and dumped at C & D processing site.
Effectiveness of desilting of storm drains
It has been seen that many drains are covered fully/partially. It has been noticed that most of the covered drains do not have access for desilting. If desilting is not carried out under the covered potion, effectiveness of desilting of rest of the drain is reduced significantly. Therefore, access points, if they are not there, should be provided at appropriate distance so that desilting can be carried out.
Schedule of desilting should be publically displayed and in a manner that is understood clearly by general public. GSDL should use the GIS layout of the drainage network made by IIT Delhi with cross-section and L-section to capture and display the schedule of desilting by the contractors segment-wise and jurisdiction-wise. Crucial details such as time schedule of desilting and the amount of silt/debris removed should also be captured and displayed.
Certification that desilting is completely and satisfactorily done, be made by the concerned agency. On this certification, local public shall be notified that work is completed and public suggestions/feedback shall be sought (through an App that allows the user to send geo-tagged photos of the concerned issue). Received public complaints should be looked into by the department within a stipulated time.
Some of the drains are managed by multiple departments/sub-divisions within departments. Extra care is required in such cases because if desilting is not carried out in proper co-ordination (there is gap in schedule of departments/sub-division or one portion is not desilted), effectiveness of the work carried out reduces significantly.
Weight & quality of silt removed should be mandatory to be certified from the way-bridge of receiving agency (Municipality SWM site). This information shall be recorded diligently segment-wise and displayed on GIS by GSDL and should be analyzed with year-on-year goal to reduce the amount of silt that is coming to the respective storm drains.
Effort should be made to put all the storm water drains under single agency that shall take care of many issues identified above. No storm water should be drained into sewer systems
No storm drain should ever outfall into sewer system at any cost since they are never designed for such situation and shall therefore result in surcharge of sewerage network and may flood some of the areas with sewage. All such cases should be identified and immediately addressed. No such cases (temporary or permanent) should ever be allowed.
Practice of opening sewer man-holes to discharge local storm water should be banned. Adequate system to discharge storm water should be put in place and public awareness should be increased towards ill-effects of diverting storm water into sewer lines.
Similarly, house-holds draining storm water into the sewer lines should be penalized. Locality level storm drains should be revived or as an alternative GW recharging mechanism should be put in place by individual household – at own cost. Awareness campaign should be carried out to sensitize public in this regard. No construction should be allowed inside any storm drains.
There are two specific violations that are usually happening:
Utilities are laid inside the storm drains
Pillars of elevated roads/metro are built inside the storm drains. No such activity should be allowed. Also, in the locations such compromise of the section has happened, adequate measures should be taken immediately to restore the original carrying capacity of the storm drain.
Design of new storm drains should not be done in isolation
Overall impact of any new drain on the existing storm drainage system should be studied.
Data collected and modeling system deployed as part of this study should be used for checking design feasibility of any new drains.
Retention cum Harvesting corridors can be laid along the road to capture the runoff generated from the surface. This will enhance the ground water recharging.
Different scenarios have been envisaged and presented in this report to simulate the prevailing conditions as well as the interventions required to alleviate the flooding conditions in various parts of the city. After implementing the recommended practices, more scenarios can be later introduced, further enhancing the efficiency of the drainage network of the city.