Houston – We ALL have a problem…

The devastating impact which hurricane Harvey has had in Houston, Texas is a wakeup call to everyone involved in property development. Motion’s Richard Bettridge argues it is now more than ever of strategic importance for flooding and flood risk to be considered and incorporated into development plans as early as possible.

The urban sprawl, which has been caused by uncontrolled development and expansion of hardstanding, increases impermeable areas producing greater runoff both in volume and in terms of peak flow. Houston has, it appears, resisted the need to ‘zone’ areas that are subject to flood risk, and although drainage connectivity has been improved through bayous and channels to convey surface runoff to safe areas, most of the drainage infrastructure has been rendered inadequate by rapid urban expansion.

There appears to be reliance on flood history as opposed to flood prediction. Furthermore tide levels, especially tide surges associated with low pressure systems, will result in high sea levels which will naturally interfere with the discharge of fluvial flows in to the bay. As such the combined event of high rainfall and high tides needs to be considered.

The position in the UK 50 years ago, despite the common misconception that we built new developments on flood plains, was to avoid development in areas which had a flood history. Flood prediction has since been required in development planning, and this has culminated in the need to take into account statistical analysis with safety factors for global considerations, such as climate change.

Ensuring safer development
Whether or not climate change is real seems to be beside the point. In the UK the concept is being used to ensure that safer development is permitted; in essence if the flood authorities are making a mistake at least they err on the side of caution. Engineers, as natural pessimists, have always done this!

Houston’s problem is reflected in the UK through the unauthorised increase in impermeable areas, through the paving over of green spaces to form private car parking, which is especially critical in urban areas subject to parking control, and through the expansion of garden patios. It is worth noting that the design of drains to collect rainwater was historically based on hard areas only, which represented a fairly small proportion of the site area.

In recent years, we have had to adopt a more holistic approach to the problem, including consideration of the permeability of soils. It is apparent that Houston is constructed on soils that are clay based and have low permeability. Hurricane Harvey will force the authorities to conduct analyses of future events in order to permit development in appropriate areas with a reduced risk of flooding.

America is the champion of the free world but this must not be conflated with the idea that development should be a free-for-all; especially when it comes to flood risk. Flood control infrastructure and flood prevention policies are critical for future development, on both sides of the Atlantic.

Richard Bettridge has worked in the civil engineering industry for over 40 years, and is a highly accomplished figure in the property development sector. With experience in flood risk and strategic drainage planning, he has project managed numerous major highways and drainage infrastructure schemes. Richard also acts as an expert witness in flooding, drainage and engineering disputes.