Hydrology in Grenada: Water is Fun, but Not Always

Grenada has many streams and rivers flowing through low valleys. These streams are part of a system of drainage basins divided by watersheds. A drainage basin is an area drained by a stream and its tributaries. The watersheds represent all the tributaries that run to a location along the stream channel. Grenada is split up into 71 watersheds. 

Retrieved from http://projects.inweh.unu.edu/inweh/display.php?ID=5618. Image showing locations of Grenada's watersheds. 

Due to its volcanic origins and mountainous terrain, some drainage patterns in Grenada are radial. The rivers and streams flow from a central high point, one of the volcanoes or mountains. Some places have a dendritic drainage pattern. The many streams join together in the tributaries of a main river, similar to the way twigs are attached to the branches of a tree. 

Retrieved from http://projects.inweh.unu.edu/inweh/display.php?ID=5618.
Image showing a high density of radial and dendritic drainage patterns within the watersheds in Grenada. 

Photo of Grenada taken during my cruise in December 2013. High points like the mountains in the background, would be a source of radial drainage patterns.

Grenada is a tropical island subject to heavy rainfall. It also has low soil permeability which means that water cannot move well through the pores. In some areas, the amount of water from rainfall exceeds the infiltration capacity. That is, how much water can move into the layers of soil. This results in overland flow, which is when water flows over the surface, usually towards a river. In Grenada, this process is responsible for the beautiful waterfalls that are located throughout the island. These waterfalls are a popular tourist destination, making them important to the islands economy, since tourism is one of the main industries. 

Retrieved from http://www.grenadagrenadines.com/explore/attractions/waterfalls/.
Annandale Waterfalls located in St. George, Grenada.

Retrieved from http://www.weather-and-climate.com/average-monthly-Rainfall-Temperature-Sunshine,Grenada,Grenada
Graph showing average monthly precipitation over the year in Grenada.

The characteristics of the island make it prone to flooding and flash floods. The high precipitation and the low soil permeability results in the rapid rise of water in the rivers. This combined with the high density drainage patterns causes a large amount of water to overflow into lower areas.

Retrieved from http://www.weefmgrenada.com/article.php?newstype=1&newsid=2535
Image shows flooded area in Grenada. The result of heavy rainfall.  

Floods can interfere greatly in the lives of the islands inhabitants. After a flood in 2011, businesses were closed, due to downed power lines. People can find themselves having to evacuate due to flood warnings. The floods have the potential to be devastatingly destructive to lives and property in Grenada.




References
https://www.oas.org/dsd/publications/Unit/oea51e/ch06.htm
http://en.wikipedia.org/wiki/Flash_flood
http://projects.inweh.unu.edu/inweh/display.php?ID=5618
http://www.weather-and-climate.com/average-monthly-Rainfall-Temperature-Sunshine,Grenada,Grenada
http://www.physicalgeography.net/fundamentals/10aa.html
http://en.wikipedia.org/wiki/Drainage_system_(geomorphology)
http://www.grenadagrenadines.com/explore/attractions/waterfalls/
http://www.weefmgrenada.com/article.php?newstype=1&newsid=2535