Seqwater explains: Why dams can take longer to fill after dry spells


Why is it that when heavy rainfall occurs in our catchments sometimes the water levels in our dams don’t rise very much? One of the main reasons is to do with our catchments are when the rain falls. A drinking water catchment is an area where water is collected by the natural landscape. It’s usually surrounded by high features such as hills or mountains. South East Queensland’s drinking water catchments provide the source water stored in our dams across the region. Soils in our catchments act like a sponge that soak up moisture When rain falls on to dry ground the water soaks in to the ground – or ‘infiltrates’ the soil. If it continues to rain, eventually the soil gets so saturated that it can’t absorb anymore and becomes surface run-off, which is water that runs over the surface of the land and eventually finds its way into our dam storages. The drier the soil is, the more water it can absorb before run-off occurs. So if the weather has been hot and dry for a long period of time a lot of rain is needed to saturate the ground before we start to see significant inflow into our dams. The amount of run-off also depends on: the intensity of the rain, where is is falling and when it is falling.

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