In our first article, on borehole drilling (find it here), we looked at the overall process of drilling. In this article, we evaluate the role of hydrologist in the drilling exercise
The recent years have seen a surge in water demand from agricultural, domestic and even industrial water uses. Thanks to this trend, the need for water harvesting interventions is now more apparent than ever. To this end, boreholes are slowly emerging as a viable alternative for water harvesting, largely because of their reliability, stability in supply and costs of drilling, which are sometimes lower than those of other water harvesting structures. The process of drilling boreholes, however, is bit technical requiring the input of experts from various fields. This piece will look at the role of a hydrologist in borehole drilling.
In the context of drilling boreholes, a hydrologist is the person who performs the hydrological survey before drilling. The science of hydrology comes in handy when drilling boreholes to understand the movement of water beneath the surface through chemical, physical and sometimes biological processes. This movement of water beneath the surface is fairly predictable once various hydrological variables are established such as the elevations and gradient of flow, information that is readily found after conducting a hydrological survey. The science of hydrology further makes it possible to understand the behavior of the water table, which is one of the primary sources of groundwater. While many assume that the water table is stagnant, thanks to hydrology, we now know that the water table is continuously changing depending on the water shed, lag time and peak flows, again, all this information is obtained from hydrological surveys.
Mostly, the water table is located above an aquifer, which is another common term that emerges during borehole drilling and subsequent surveys. The term refers to the water trapped in void spaces beneath the surface, which can be abstracted after drilling. This storage and abstraction ability is denoted by the term hydraulic conductivity, which varies depending on the type of rocks or soils in an area. For example, sandy rocks have a higher hydraulic conductivity compared to other soil types, implying the former can store underground water more reliably compared to the latter. In hydrology, aquifers are deemed as either confined or unconfined. The latter denotes an aquifer with water trapped between two non-permeable soil layers, creating a pressurized water zone, which sometimes feeds into a water table to create an artesian well. Unconfined aquifers, on the other hand, comprises of water trapped between a permeable and a non-permeable layer. With a hydrologist on site, all these variables can be established, increasing the probability of finding a reliable supply of underground water for borehole drilling.
Once the hydrological survey has been conducted and subsequently a borehole has been drilled, the next stage of the process is usually to conduct pump tests. These tests are done to establish the drawdown factor. The drawdown factor informs the level of natural seepage that drains into the water source where the borehole is sunk and not, other nearby streams and wells. With this data, one can estimate the reliability of the borehole to supply a specified amount of water over time. All these technical details aside, the costs savings that come from hiring a hydrologist during borehole drilling are perhaps the greatest benefit of hiring one. In that regard, based on conducted surveys, hydrologist not only inform the proper site to sink a borehole; moreover, they estimate the depth of drilling, which is used to calculate the costs of sinking the borehole-usually, this costs are estimated per meter of drilled depth. The hydrologist also reduces the chances of drilling and hitting a dry well, which is a fairly common site in instances where boreholes are sunk without the input of one. The final and probably, the most important reason for a hiring a hydrologist is legal compliance. Kenyan law requires the submission of hydrologist report to accompany the documentation of any borehole drilling exercise.