The importance of the Feasibility Stage investigation of a new project cannot be overestimated. It is the key phase that provides the client with the numbers at a relatively high level, to decide whether to proceed with a project. Getting it wrong at this stage can result in a nasty surprise down the line when the project either fails to deliver the promised benefits or worse – a fatal flaw is discovered. The earlier in the project cycle that fatal flaws can be ruled out and project feasibility can be proven, the less chance there is of spending money on detailed design, tendering or even construction of a project that later turns out to be a dud.

One of the biggest risks to a meaningful feasibility investigation is Client and Consultant bias towards a favourable outcome. Termed “Optimism Bias”, the client is desperate for their project to succeed and deliver a promised return to their enterprise. There is also the belief that the Engineer is being paid, so they must make it work! The Engineer is excited by the project challenges, is driven by a can-do attitude, and may be looking forward to the prospect of future work on the project. Neither party wishes to contemplate the possibility that the project simply may not be viable, and should be terminated. Yet in some cases, spending a little more time and money on this phase of the project, even if it delivers an unfavourable result, can be the best money the Client ever spent. There are many examples of “white elephants” that have been built and never used properly, either because the client and engineer were both blinded by their unbridled optimism for the project, or because the Engineer could not bear to deliver “bad news” to the Client at feasibility stage.

Mike Udal of MBB Pietermaritzburg recently travelled to the Iringa region of Tanzania to undertake the feasibility investigation of a dam site for a small farm growing high-value produce. They badly need additional water to expand their irrigation and ensure the viability of the farm. However, they are located towards the top of a hill, and there are no streams on the farm from which to draw water. There is however a shallow valley located towards the boundary on one side of the farm and it was this valley that provided the hope that a dam could be built.

Armed with GPS survey equipment and a negative COVID test, Mike travelled to the site and met with the owner to review the proposed dam location. Initial impressions were good – the site has exposed rock boulders at the surface, and 2 test pits were immediately started along the foundation alignment to investigate the depth and nature of the subsoil. While these were being dug, Mike surveyed the basin in enough detail to produce an accurate model of the basin and surrounding area, and to therefore determine the storage that could be created if a wall were to be built. The survey was tough going in amongst established Miombo woodland… every tree had a spiders web strung to the next tree, and the rain showers were heavy and frequent, leaving the rocks wet and slippery.

The dam foundation proved to be good! Shallow rocks were evident in both pits dug, and the subsoil was uniform clayey sand. Enough clay fraction that the wall would seal, and enough sand fraction that the wall would be stable! Good news so far!

When the survey was downloaded and analysed, a different picture emerged. Although there was no technical reason a dam would not work, the catchment was steep and the valley was relatively open and wide. These factors lent themselves to a high, long wall, for relatively low dam storage. In fact, the ratio of embankment volume to stored water volume held constant at 1:1 over several depth/capacity scenarios – not good, especially considering that this is a worse ratio than you would achieve if you simply dug a storage dam as a hole with compacted embankments on a piece of level ground!

Further downslope, the valley widened even more, and there was no prospect of improving the economics of the dam within the existing farm boundary.

It was with disappointment that the early results were presented to the client, who reluctantly agreed that the dam was simply not feasible, based on the economics of the construction, and that the project should be terminated immediately. Other water sources are the only option for water supply going forward – however, a dam storing surface water on the farm is simply not feasible.

In providing this assessment, MBB lost out on the detailed design and construction management of the proposed dam, and the Client’s hopes for a dam to secure their future water requirements were dashed. However, there is the satisfaction of knowing that ultimately, the correct information was provided to the Client in an objective manner which enabled them to make the correct decision, ultimately spending a little bit of money to save a lot!

There is a big difference between a disappointed Client and an unhappy Client. In this case, the Client is undoubtedly very disappointed with the outcome, but happy to have been presented at a very early stage with the basis on which to make a sound decision. A strong relationship of trust has been established, and word travels far. Perhaps there will be future work coming out of Iringa, either from the same client or other farmers in the region. We can only wait and see.