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Water and suspended sediment inflows, transport, volume changes, and outflows determine the environment for aquatic plants and animals in a given reach of a river. Lock and Dam 19 at Keokuk, Iowa is the oldest and highest of the 27 lock and dam structures that maintain adequate depths for navigation by 2.75-m draft barge tows on the Mississippi River between St. Louis, Missouri, and Minneapolis, Minnesota. Pool 19 is used as an example for various measures of water and sediment transport and variability.The 104-year water discharge record at Keokuk, Iowa is used to demonstrate the average conditions and variability of water discharge. Major tributaries to Pool 19 illustrate the importance of local inflows even when they appear insignificant compared to the Mississippi flows. Flow duration and the annual cycle of high and low flow periods are presented. Sediment budgets are developed from suspended sediment measurements. Sedimentation survey data are used for developing historical sedimentation rates and determining the loss of volume in the pool. Combining the sedimentation survey and the suspended sediment budget analysis yields a present volume equal to 45% of the original.The flood of 1973 and the drought of 1977 are used to illustrate the impact of extreme events on the riverine ecosystem. The 1973 flood set the record for daily discharge and ranks second in annual volume. The 1977 water year ranks third lowest in annual volume and had no spring flood. The drought had a more persistent impact on the ecosystem than the flood.Though Lock and Dam 19 is the only one with crest gates and a hydropower plant, Pool 19 has water discharge and sediment transport characteristics that are typical of the Upper Mississippi River navigation pools.

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