|Groundwaters do not exist as an underground lake in our region|
Image courtesy of International Association of Hydrologists
One area that is not understood is that groundwater usually discharges somewhere. Sometimes groundwater discharge is obvious through springs. But where it intersects with permanent surface water it is much less obvious. The Evans Head area is a good example of where discharge from the Woodburn Sands aquifer and broader Coastal Sands aquifers is concealed.
|Spring-fed creek on Chinaman's Beach.|
While walking along Chinaman's Beach south of Evans Head during a recent long dry spell, I couldn't help notice the dark coloured water flowing over parts of the beach. This is one of those discharge areas I'm talking about (most people might be more used to seeing freshwater flowing over a beach from contaminated urban stormwater drains). The coastal sands above Chinaman's Beach holds groundwater and slowly discharges it at the beach. The dark colour of the water is from dissolved humic matter from coastal vegetation soaking into the sand. Tasting the water it was apparent there was no salt in it and understanding the groundwater area I knew it was clean. The springs I observed on Chinaman's Beach were obvious areas of groundwater discharge. The vegetation in the springs was lush and clearly reliant on the groundwater. This is formally known as as groundwater dependent ecosystems.
The lesser known discharge is not all through visible springs like those on Chinaman's Beach. Much of the discharge from the coastal sands aquifers is actually concealed by the sea. It might be a surprise to many in some areas just off the coast there are zones with freshwater. The amount of water that can be discharged underground into the sea can exceed the discharge from terrestrial springs (e.g. Santos et al. 2009). These are the undersea equivalent of the Chinaman's beach springs. This is interesting from a aquatic ecology point of view because it may mean that there are ecosystems in the ocean that are dependent on freshwater! That is, groundwater dependent ecosystems in the sea.
Groundwater is an interesting feature of our region. It is a source of drinking water, irrigation water and even industrial water. It is often important as some ecosystems are dependent on it. It is also surprising since ecosystems can be dependent on fresh groundwater even when out to sea.
Postscript: about a month after this blog post a story emerged in the local newspaper about sinkholes or zones of quicksand on Chinamans Beach. These quicksand 'pits' look just like typical groundwater discharge areas. The Northern Star article can be found here.
*Santos, I.R, Burnett, W.C., Chanton, J., Dimova, N. & Patterson, R. (2009). Land or Ocean?: Assessing the driving forces of submarine groundwater discharge at a coastal site in the Gulf of Mexico. Journal of Geophysical Research. vol114.