Water Quantity

The Breede River is about 257km long and has a catchment area of about 12 625km2. Runoff from the catchment is highly seasonal with high flows and floods in winter and low floes in summer. With the creation of all the dams in the catchment, the mean annual runoff has been reduced by approximately 42 percent from the reference conditions to present state.

 

Fresh water brings in cold oxygenated water bring down nutrients from the catchment. Besides having managerial impacts, fresh water is needed for certain species niche needs. Certain species require differing fresh water levels for some part of their life cycles. High saline levels may cause die back of fresh water species and usually affect the species that can tolerate certain saline levels but only for a certain amount of time such as reed banks.

 

Fresh water inflow is also necessary for flushing of the estuary. Sediment brought down from the catchment deposits along its course and excess sediment is usually pushed out of the mouth. The fresh water flow needs to be strong enough to counteract the oceans sediment input to push this sediment out of the mouth. A lack of fresh water flow could result in the shallowing of the estuary and the creation of sandbanks.

 

Water quantity is the most important factor determining the classification of an estuary (we are at present classified as a Category B estuary). This available fresh water is sought after by most landowners on the river from source to the mouth and an understanding of water use and availability is of huge importance in preventing damage to the system.

 

Fresh water flow is monitored by the Department of Water Affairs and is made available to the LBRC. The LBRC collects this data weekly and stores it in a database for analyses.

 

 The upper river where the water is fresh enough to let the reeds grow

 

Episodic events

 

Episodic events in this context refer to droughts and floods. These are normal events that occur that have dramatic effects on the estuary. Flooding will flush the system and is highly necessary. Floods also have a major effect on the developments along the estuary and therefore floods have managerial impacts. Droughts are more difficult to monitor, but also have effects on the system usually creating a highly saline system that will affect saline intolerant species especially further upstream. Most of the management implications are reactive, with flooding one will have disaster management and with droughts it may be necessary to request the release of fresh water from dams upstream.

 

The LBRC makes sure they collect as much information in times of these episodic events as possible. Having long term data on these events will allow us to identify trends that may be used in the future to avoid the level of damage these events may cause.

 

One of the floods to hit the Breede River (2008, Picture by Gerrard Hoek and Marius Heyneman)