Streamflow

A diversity of biological species, from unicellular organisms to vertebrates, depend on flowing-water systems for their habitat and food resources.

[1] Streamflow is the main mechanism by which water moves from the land to the oceans or to basins of interior drainage.

Rivers are always moving, which is good for environment, as stagnant water does not stay fresh and inviting very long.

A stream gauge provides continuous flow over time at one location for water resource and environmental management or other purposes.

[5] For purposes that do not require a continuous measurement of stream flow over time, current meters or acoustic Doppler velocity profilers can be used.

This method involves building a graph in which the discharge generated by a rainstorm of a given size is plotted over time, usually hours or days.

It is called the unit hydrograph method because it addresses only the runoff produced by a particular rainstorm in a specified period of time—the time taken for a river to rise, peak, and fall in response to a storm.

Plotted on a graph, these data from the unit hydrograph for that storm, which represents the runoff added to the pre-storm baseflow.

Given several decades of peak annual discharges for a river, limited projections can be made to estimate the size of some large flow that has not been experienced during the period of record.

The technique involves projecting the curve (graph line) formed when peak annual discharges are plotted against their respective recurrence intervals.

As rains continued, surface depressions, wetlands, ponds, ditches, and farm fields filled with overland flow and rainwater.

With no remaining capacity to hold water, additional rainfall was forced from the land into tributary channels and thence to the Mississippi River.

For more than a month, the total load of water from hundreds of tributaries exceeded the Mississippi's channel capacity, causing it to spill over its banks onto adjacent floodplains.