How Dhaka’s drainage and natural hydrology can be improved
Dhaka is known for water-logging and drainage congestion, losing its past glory of natural khals and wetlands full of fresh water. Wetlands in Dhaka are divided into two categories: Water bodies and lowlands -- which comprises of surrounding rivers, lakes, ponds, khals, and low-lying areas. The surface water area of Dhaka Central Region is about 13% of the total land area. Our drainage has two aspects: Flood protection and storm-water discharge, which are interrelated.
The capital’s water resources are threatened by both human activity as well as natural causes. Climate change is affecting our city, in particular, in three ways: Increased frequency of floods, drainage congestion, and heat stress. Because of its geographic location, Dhaka suffers from river floods annually. The city also suffers from frequent storm water flooding. The illegal encroachment of rivers, water bodies, lands filling, and indiscriminate dumping of domestic and industrial waste into rivers and canals are accelerating the drainage congestion. As a result, Dhaka faces severe storm water flooding during heavy rainfall.
The city corporations and the institutions empowered with various planning and management responsibilities have been nothing but feeble in taking appropriate approaches to tackle these issues.
The local surface water hydrology around Dhaka is complex -- the Dhaleswari River, a tributary of the Jamuna River, flows by the south-eastern part of the North Central Region of Bangladesh, close to the confluence of the Padma River and Upper Meghna River. The Lakhya River joins Dhaleswari at 11km downstream of the Buriganga confluence. About 5km below the Dhaleswari-Lakhya conﬂuence, the Dhaleswari meets the Meghna River, which in turn flows into the Padma River, a further 20km downstream.
All of this results with the city’s drainage system being under the influence of backwater effects from surrounding rivers.
The city has been experiencing a gradual increase in water-logging over the last decade, of course. Moderate-to-heavy rain causes serious drainage problems in many parts of the. The process of rapid urbanization is not focusing enough on adequate drainage facilities, which causes water-logging and temporary inundation in parts of Dhaka for several days during monsoon.
This has brought the reality that, during the monsoon, the city’s drainage depends very much on the water levels of the peripheral river system. The situation worsens when monsoon runoff, generated due to continuous rainfall, coincides with high water level in the river systems.
Encroachment of surface water bodies can aggravate the risk of water-logging; micro-drainage system cannot carry out the load and they are not being upgraded, maintained, and managed on a regular basis; and poor, partial, and overloaded sanitation can pose serious health hazard to the dwellers during water-logging particularly in the low lying areas.
Needless to say, flood prevention is necessary to avoid damage to property and life.
Over last few decades, development in the flood flow areas within Rajuk jurisdiction has been going on despite planning and legal restrictions. But poor monitoring and lack of enforcement of plans and legal powers have so far failed to put a dent on most of these activities.
Once a restricted low land is filled up and inhabited it is almost impossible to reverse the situation from practical point of view.
Such activities promote development in these areas but they have adverse impacts in the long run. The authority should build a conservation zone which especially includes flood flow and water retention area that must be preserved for maintaining a sustainable environment of the Dhaka Metropolitan Region.
The city authority should adopt legal measures and innovation of economic use to preserve retention ponds. All development in the eastern fringe areas should safeguard the retention pond areas and khals; all private housings within the eastern fringe areas should incorporate flood water management and higher level (Structure Plan and Detailed Area Plan) road proposals.
Policies on drainage and hydrology were provided in the Dhaka Structure Plan in 1995, where policies were set on flood control, flood flow zone, and drainage. A structure plan was followed by Detailed Area Plans (2010) where more detailed proposals were made based on the policy framework of the structure plan.
DWASA has been preparing detailed and comprehensive Storm Water Drainage Master Plan for an efficient drainage network for greater Dhaka City, which will be treated as a basic document for storm-water/manmade drainage network plan for DAP, 2016-2035.
The important point to note here is to ensure the proper and timely implementation of these policies and plans.
Moreover, it is imperative that we develop a comprehensive Watershed/Water Resources Management Action Plan that would account for the impacts of climate change and adaptation measures conforming to future urban development plans.
Tanvir Ahmad is an urban planner.