Guidelines for Emergency Post Flood River Recovery

Guidelines for Emergency Post-Flood River Recovery

James G. MacBroom, P.E.

Milone & MacBroom, Inc.

Floods are natural events that impact both natural and built environments, resulting in ecological and community damages.  Extreme floods can reshape high energy channels via incision, head cuts, and mass bank failures that create high sediment loads.  Downstream and lower gradient river reaches are prone to aggradation, channel widening, alignment changes, and sudden avulsions.  Floods also create meander cutoffs, floodplain side channels, bury wetlands and oxbows, and leave floodplain deposits.  Extensive river infrastructure damages also occur, including culvert and bridge blockages, damage, and destruction.  Local communities respond immediately after floods to address public safety, repair critical infrastructure, and provide emergency services, often with limited funding, technical resources and training.  Unfortunately, observed emergency responses often include excessive channelization with dredging, straightening, bank clearing, armoring, discharges, and homemade levees without adequate oversight, leading to further ecological damage and non-sustainable channels.

There is a need for clear simple guidelines for use by public agencies, contractors, and landowners with minimal professional advice for emergency post flood river repairs that cannot wait for normal studies, surveys, designs, permits, and bid processes. The initial verbal policies and instructions issued during recent floods have gradually evolved into written guidelines that can easily be reproduced and distributed. They are for use during the earliest phase of post-flood recovery operations prior to long-term and permanent planning.  The guidelines are specifically intended to aid field decisions and schematic designs for immediate construction.  The guidelines emphasize goals and objectives for alluvial, threshold, and non-alluvial channels, river processes and geomorphic principles, with selected references for further information

The first step is a rapid river assessment to classify river processes, risks, and damages to rank priority sites and limit unnecessary channelization at low risk sites. The recovery guidelines address channel alignment, profile, dredging, floodplain connections, channel cross sections, bankfull dimensions, use of compound channels, fish passage, culvert replacement, debris, and regulatory permits.

1000-01-2-mr912-rpt.doc