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4.4: The Water Balance of Lakes

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  • Lakes have many sources of both inflow and outflow. The main sources of inflow are:

    • streams
    • precipitation onto the lake surface
    • ground water

    The main sources of out flow from a lake are:

    • streams
    • evaporation from the lake surface
    • groundwater

    Various configurations of streams are possible:

    • Stream or streams flow in, stream flows out (Figure 4-3A). Usually only one stream flows out. In this kind of configuration the stream can be viewed as simply a fat place along a river. This is the most common kind of lake.
    • Stream or streams flow in, no stream flows out (Figure 4-3B). The loss is made up by groundwater outflow and/or net evaporation. This is common in arid and semiarid regions; the streams are usually ephemeral. Lakes like this tend to be playa lakes. The Great Salt Lake is a good (and large) example.
    • Stream flows out, no stream flows in (Figure 4-3C). The lake is fed by groundwater, usually not just by precipitation.
    • No stream flows in, no stream flows out (Figure 4-3D). The lake is both fed and drained by groundwater movement. Lakes like this are common in glaciated areas underlain by a thick mantle of highly permeable glacial sediment, as on Cape Cod.

    Fig. 4-3.png

    Figure 4-3. Configurations of streams flowing into and out of lakes.