Narrowed Streams Contribute to Flooding in E-11: Study – Journal

ISLAMABAD: A new hydrological study conducted by the Army’s Directorate of Design and Consultancy (DD&C) found that natural waterways had narrowed in E-11, causing urban flooding Last year.

The study, however, proposed interventions and a mitigation plan to avoid such flooding in the future.

The report of the study published on August 16 said: “The simulations revealed that all the drainage channels in the area overflowed their banks into the built-up area. However, no watercourse overflowed its banks outside the developed area.

In July last year, due to a narrowing of a stream that enters the area from the E-12 side, urban flooding occurred in the Pakistan Medical Cooperative Housing Society (PMCHS), leaving a woman and her child dead in addition to inflicting losses on property and several vehicles.

The area – which was exempted from land acquisition by former President Ayub Khan due to the Golra shrine – is home to unauthorized companies, operating without valid no-objection certificates and more than 70 unauthorized high-rise buildings . Most of these buildings were constructed in the last decade but the Capital Development Authority (CDA) failed to stop their construction as in most cases it was limited to issuing opinions only .

The army leadership proposes various interventions to reduce the risk of overflowing water channels

Following the flood and the death of the woman and the child, the CDA decided to engage DD&C to carry out a hydrological study in the area.

The analysis revealed that the natural hydrology and natural flow paths were significantly altered during the development of the PMCHS as well as throughout Sector E-11. In 2011, one of the main rivers, Jod Khas, flowing through PMCHS was reduced to three meters, according to the study.

Similarly, another stream was straightened and narrowed to nearly two meters, its surface having been paved over and contained by a wall of stone masonry on each side. A third watercourse running through the company was also confined to a deep channel lined with stone masonry and paved at its base. A box channel passed through the built-up area with different cross-sections and made numerous right-angle bends in its path.

“It has been erased from the old data that the developed model applied in PMCHS and E-11 had invariably narrowed, straightened and paved the natural drainage channels. Buffer zones were completely missing and properties were built right up to the edges of these narrowed channels,” the study found.

“It is evident that the natural drainage network has shrunk considerably across the whole area,” he added.

The study further indicated that the narrowed right-of-way (ROW) of natural drains was the greatest structural shortcoming in handling peak flooding in E-11.

“In addition to this, the narrowed right-of-way has been further encroached by some properties, which appears to be causing a backflow pond – resulting in the culvert overflowing onto the dual road within the northwest perimeter of the E-11 area,” said he declared.

Conversely, if the right-of-way of natural watercourses is restored in the sector to the extent of what is estimated on Maps 19 and 20, the risk of flooding would probably be completely eliminated. However, since the properties have already been built within the right-of-way reclaimed from natural drainage, restoring the right-of-way to its original boundaries can be costly (for builders and owners) and may involve other complexities. .

He said that as long as the area continues to operate with a constricted right of way of natural drains, the risk of flooding will threaten residents of E-11 in the flood zone.

The study proposed interventions, “which are deemed to be effective and feasible under current development with minimal requirements for demolition of existing buildings and/or infrastructure”.

Suggested interventions are: water-sensitive urban design, introduction of swales, intervention of impoundments, creation of a drainage network, swales in main boulevards, trenches charging station in residential streets and the drainage swale through the PMCHS.

Recommending flood risk management in flood zones in general and E-11 in particular, the study said flood zones should be assessed and mapped and residents should be provided with flood risk maps. The monsoon should be declared as an emergency flood season for vulnerable areas, basements should not be rented/used for habitation and any planned structural interventions for flood mitigation should be preceded by a holistic hydrological model.

The study also recommended that the waterways in E-11 be improved by removing the concrete/masonry revetment and replacing them with boulders, gravel and sand.

This will improve groundwater recharge. He said all sections of waterways covered with concrete slabs should be demolished and this practice should be strictly prohibited.

The study also called for the widening of narrowed streams, where possible, adding that some properties had still encroached on the narrowed streams that should be identified and removed. He also called for a sustainable development model for the sector in addition to updating the region’s regulations with modern tools.

CDA officials said the recommendations will be implemented and stakeholder meetings will be held soon in this regard.

Posted in Dawn, August 24, 2022

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