I have listened with great interest to the raging public debate about whether or not it was the right choice by citizens to construct their homes on the banks of the Sandy Gully Scheme (SGS), in light of the various structural breaches of its retaining wall.

The Sandy Gully Scheme is the wide network of major and minor open channels that deposits storm water drained from the urban infrastructure of most of St Andrew to the sea at Hunts Bay. The two major channels are referred to as the Sandy Gully and the minor channels have various names such as the Rochester Gully, Barbican Gully, etc, each of which assists in conveying storm water into the Sandy Gully. Gully banks are the immediate surface area of the soil being restricted by the rubble stone retaining wall of any open channel that constitutes the Sandy Gully Scheme.

Discussions have highlighted the shortfalls in Jamaica’s poor enforcement of building regulations as it relates to locations where individuals are permitted to build a structure. From the perspective of many Jamaicans, it makes no sense to live in such proximity to major waterways that have the potential hazard of overflowing and causing flooding. Overflowing should be only one of the many concerns. However, regardless of the majority of Jamaicans having such a perspective, the reality is that there are people who work all their lives and are unable to buy land to build their houses so they choose the most likely parcel of land available to them – a gully bank – which is not outside of the statutory setback from the retaining wall.

The regulating authority may say it’s not an easy task to ensure that all structures have the necessary setback from the retaining walls of the various open channels of the Sandy Gully Scheme, but this is an unacceptable excuse. Herein lies the problem: the lack of will to stringently enforce our building regulations. The Jamaica Development and Investment Manual and the Town and Country Planning Act are some of the documents that have been compiled by policy makers which detail building regulations for Jamaica. With that background, the necessary resources should be provided and implemented to ensure strict enforcement of building regulations. Such a move will surely take us closer to the much talked-about developed country status.

Nevertheless, with all the above, has anyone asked why there are so many structural breaches of retaining walls throughout the Sandy Gully Scheme? The failure of these retaining walls has raised many eyebrows, particularly in structural engineering circles. Without delving too much into the fields of Fluid Dynamics, Fluid Mechanics and Structural Designing, most of these failures could have been avoided if a proper maintenance programme was implemented for the scheme to ensure the structural integrity of the overall system.

It is believed that a hydraulic jump as a result of a structural breach of the slab of the open channel was responsible for the tragedy at Sandy Park. The hydraulic jump caused storm water being transported by the channel to elevate and leave the channel, destroying the system itself and causing death to people who were too close to the retaining walls of the open channel in the event it overflowed. And overflow it did. However, what caused the overflow is of importance to an individual with an engineering background. The water infiltrated behind the then existing retaining wall, creating an increase in hydrostatic pressure which caused the wall to fail. This then caused a family house of six to fall into the raging waters and they all lost their lives. Therefore, the question is, without tolerating the incorrect practice of building on gully banks without the necessary setback, what if that structural breach was not present in the slab of the respective open channel?

It should also be noted that some of these rubble stone retaining walls are about 50 years old. Have they outlived their usefulness? Some may say that a structure of such magnitude and importance should have been designed for a 100-year flood, but to my knowledge, in terms of capacity and speed in which water is drained through the system, the Sandy Gully Scheme is doing an excellent job. The real problem is that the man-made structure is not being maintained properly, which is essential to any man-made structure for it to remain structurally sound and functional.The powers that be might say otherwise, but on a number of occasions I have seen damaged areas of slabs and cracks in rubble stone retaining walls which pose imminent danger and might lead to problems of greater magnitude in the near future.

Everton Smith is a junior structural engineer.

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