EFFECTS OF HYPOTHETICAL LAND SUBSIDENCE ON PEARL RIVER FLOOD PROFILES
by M.N. LandersPrepared by the U.S. Geological Survey
CONTENTS
Introduction
Land subsidence
Methods
Discussion
Water-surface profiles
Depth Profile
Pearl River
Summary
Selected references
FIGURES
1. Pearl River in the vicinity of Jackson, Mississippi
2. Generalized diagram of land subsidence on a large stream valley and its effects on flood depths
3. Observed and computed profile of Pearl River through Jackson, Mississippi
4. Channel and water-surface profiles before and after subsidence for a synthesized stream reach
5. Channel and water-surface profiles before and after subsidence for a synthesized stream reach
6. Channel and water-surface profiles, before and after hypothe- tical subsidence of the Pearl River through Jackson
7. Relation between maximum drop in water surface and maximum vertical subsidence for streams with 0.10-percent slope and 0.02-percent slope.
ABSTRACT
Land subsidence has been documented in numerous areas where large ground-water withdrawals have led to the consolidation of under- lying sediments. Potential flood hazards, due to subsidence, have long been recognized for coastal backwater-controlled streams, but not for upland streams where these effects are more complex. Subsidence in the Jackson, Mississippi, area was identified, al- though not well defined, in a study by Chi and Reilinger (1984). This paper discusses the effects of land subsidence on flood profiles, based on the analyses of two stream reaches. The first is a synthesized stream reach having uniform slope and conveyance characteristics equivalent to a large, slope-controlled Mississippi stream. This synthesized reach provides a simplified case where only subsidence causes variations in the flood profile. The second case is a reach of the Pearl River through Jackson, Mississippi, from below Ross Barnett Reservoir downstream for about 19 miles to the vicinity of Byram (fig. 1). Channel geometry for both cases was altered to represent hypothetical subsidence occurring in the stream reaches. A range of vertical and areal amounts of subsidence was imposed on each stream. Relations between flood depths and the vertical and areal amount of subsidence are defined by the flood profiles computed for each case. These relations are very sensitive to stream slope. The results presented are useful in understanding and evaluating flood hazards where subsidence coincides with the flood plain of a large, upland stream.
LizardTech's Djvu plug-in is needed to view these reports.
CLICK HERE TO VIEW THE ENTIRE REPORT
For questions or comments, contact K. Van Wilson.