Professional Presentations:

Levee Stability Impacts from Seepage Induced by Delta Island Flooding; Hultgren, Edwin M.; CALFED Bay-Delta Program Science Conference, Sacramento, California; October 3-5, 2000. - Interior elevations on deep peat islands range from 10 to 20 feet below sea level.  Most farmers and their reclamation district engineers on deep peat islands have reported seeps or wet spots at or near levees that have developed and remained continual sources of concern.  Seepage has appeared following dredging in adjacent channels and after an adjacent island’s levee fails and the adjacent island floods.  Water storage on islands within the Delta could create conditions similar to a flooded island.  Common stratigraphy beneath the islands in the central Delta consists of peat over sand. 

The sand aquifer is believed to be continuous between islands, and most certainly across man-made cuts.  Flooding of a delta island raises the head in the underlying aquifer.  Lateral seepage through the aquifer can raise the groundwater level beneath adjacent islands.  Flow-nets of seepage are presented.  The impact of increased seepage on levee stability is discussed.  Methods to control seepage are described.  Sensitivity of slough bottom conditions is considered.  The benefits of relief wells during flood stage are discussed.