Realising that Kochi does not have scientific storm water and sewage management strategies, a Non Motorised Transport (NMT) master plan drawn up for Kochi metro proposes a four-pronged strategy for localised mitigation of waterlogging.
The master plan reaches the conclusion that Kochi does not have adequate storm water and sewage management strategies based on primary and secondary data.
“As a consequence, it is noticed that in most cases, storm water drains in Kochi also carry sewage, thereby polluting waterbodies and environment. It is recommended that a detailed proposal for storm water management and sewage or sanitation be prepared for Kochi,” says the master plan under the heading “some of the methods that can be explored while designing road space to ensure localised mitigation of waterlogging.”
One of the proposed methods is bioswales, which is a modified variant of swale, and typically has water tolerant vegetation that uses bio retention methods to improve water quality, reduce the run-off volume, and modulate the peak run-off rate while also providing conveyance of excess run-off. Planter beds along footpaths were another recommendation. Planter beds are contained landscape areas designed to accommodate plantation, and at the same time capture and retain storm water run-off. Infiltration and flow-through planters are structural landscaped reservoirs used to collect, filter, and infiltrate storm water run-off. Flow rates and volumes can also be managed with infiltration planters.
Green gutters, which are similar to flow-through planter with narrower width of the green area, was another proposed method for storm water management to prevent waterlogging. They require a long, continuous space to effectively slow and filter pollutants but are very shallow and do not retain large amounts of run-off.
However, the master plan proposes water recharge pits facilitating collection, cleaning and charging as the most feasible solution to storm water management considering the space requirement. The physical, chemical and biological quality of the recharge water affects the planning and selection of recharge method.
The master plan says that the design of road spaces can consider provisions for local storm water management strategies, wherever possible. As per the Indian Road Congress code, Design Strategies for Storm Water Drainage System, the principle behind modern day storm water management strategy is to capture rainwater in smaller zones throughout the city and recharge the water back to the ground or nearby natural water channels through natural or mechanical means.
“This can reduce the overall road run-off thereby possibly reducing water logging within the city. Even when the rainwater recharge fails due to high water table, natural filtration of rainwater and subsequent disposal into nearby natural water canals can ensure higher efficiency of such canals with lower pollution levels,” says the master plan.
