How to calculate groundwater flow direction?
Groundwater is water that sits below the unsaturated zone of the soil, it's often found in aquifers, large pools of water that form in this layer or between rocks. Groundwater always flows downhill from areas with low amounts of groundwater to discharge points with high amounts of groundwater such as rivers, sea and valleys. However, to find the direction of flow is not always as simple as calculating the elevation of the area. There are several other factors that need to be taken into consideration to calculate the exact path of the groundwater in any particular area. Things to consider include the number of aquifers that are situated in the groundwater and how these are connected.
It is important to calculate the flow of groundwater when setting up a groundwater extraction site or sampling the groundwater near a potential pollutant such as a landfill site. If the groundwater flow is not correctly determined then the samples will be taken in the wrong area, making them void. Other areas of groundwater could then become contaminated without the company actively monitoring these. This could have serious implications for the surrounding environment and population.
There are several different methods that can be used to find out the direction that groundwater flows, we take a look at a few of these options in this article. This article is for information only, companies should do their own research when determining the groundwater flow direction in a particular area.
Observing surface water drainage
Surface water drainage patterns can give a good indication of how groundwater is flowing and in which direction. Surface water often emulates ground water, so by closely monitoring surface water it can provide an indication of the direction of flow of groundwater. However, this can only provide an indication and further methods of investigation are needed to determine the exact groundwater flow direction.
Environmental research papers
In many areas of the world groundwater is a valuable resource that is used for providing drinking water, growing crops and much more. In areas such as this having full knowledge of the direction of flow of the groundwater is very important for the environmental bodies. It is also essential that the groundwater is not contaminated by landfill sites, leaky underground gas tanks or overuse of pesticides. With this importance in mind some environmental agencies conduct extensive research into the groundwater flow direction and plot their findings. This research is often published and made available for businesses to access and use. Always check with environmental agencies before conducting your own research.
The hydraulic gradient is the force that drives groundwater to move. By measuring the hydraulic gradient in several areas in a single aquifer the direction of the groundwater flow can be determined. The hydraulic gradient needs to be measured at 3 points to determine the flow of the groundwater. This must be done at measured intervals in a triangle formation. Calculations can then be made to view the level of water at each of the points.
Measuring the groundwater flow direction is a sophisticated science that requires different levels and complexity of measurement depending on the area in question. This article is provided as a basic guide in order to help initiate further research into the topic.
At QED we supply groundwater monitoring and sampling equipment. Our equipment can be used to determine if groundwater is safe for extraction and drinking. Groundwater sampling can also be required to ensure compliance with environmental regulations. Sampling is conducted through a well or using a bore hole that penetrates through the top layer into the saturated zone. A bore hole is only approximately 6 inches in diameter but provides enough width for sampling to take place.
Sampling can use pumps or passive sampling in order to take the water out of the borehole or well. Passive sampling does not require a pump to refresh the water before the sample is taken. It is one of the most reliable and effective ways to gather groundwater samples, especially from wells with low water levels. Pumps can either be temporary or permanent depending on the use of the groundwater and how often samples are required.
Find out more about how QED can help with groundwater compliance, monitoring and sampling.