|
Objectives
The objective the flood zone determination project was to develop
a methodology for local governments that would allow them to more
easily update flood discharges, elevations and flood boundary maps
using high resolution remote sensing. Timely updates are needed
by rapidly growing communities because it is this increase in impervious
surface which increases flooding. Cities must enforce regulations
to restrict building in the floodplain. These regulations are tied
to requirements of the Federal Emergency Management Agency (FEMA)
Flood Insurance Program and to other local building regulations.
The FEMA flood study for Columbia, MO published in the early 1980’s
was based on watershed development at that time. The study was updated
slightly in the early 1990’s, but with no more recent development
information. This reliance on outdated flood maps is a problem in
most cities in the U.S. The results of this project will assist
cities and their consulting engineers in using remote sensing to
update these maps and conduct other storm water planning and management.
User Community
The user community for the flood zone determination project consists
of several separate, but related users. The first set of users are
engineering consultants who will incorporate the remote-sensing
derived information into flood elevation assessments. Other users
include individuals in local government who must make decisions
on a daily basis regarding building permit approvals. Additional
end users are the property owners and builders whose property will
be affected by the results of the flood zone determination. These
additional end users and their consultants will closely scrutinize
the results and may also use remote-sensing information as part
of legal challenges to the local government’s flood zone decisions.
Users from the City of Columbia and Boone County requested the development
of this capability. The Bear Creek Watershed was selected for this
flood zone prototype and it is located within the city limits, so
the City of Columbia is the actual end user.
Product Devolopment
The flood zone determination products utilize a direct land cover
classification developed from IKONOS 4 m multispectral imagery to
assess the potential for rainfall to be converted to storm water
runoff. This is in contrast to current practices that rely on land
use classifications and zoning (e.g., residential, commercial) within
the urban environment to estimate land cover (e.g., woods, grass,
impervious surfaces). The land cover classification is used to generate
a weighted average curve number for an area under analysis. The
curve number is used in hydrologic modeling to determine the peak
discharges associated with ultimate development. Peak discharges
are used with a rating curve developed from previous FEMA hydraulic
modeling (i.e., determination of water surface elevations associated
with various flood events) to determine the peak water surface elevation
for the calculated peak discharge. Peak water surface elevations
are applied to a digital topographic map to indicate those locations
expected to be flooded during a 10-, 25-, 50- and 100-year rainfall
event. Overall products thus include the land cover classification,
curve number distribution, peak discharges, flood elevation estimates,
and maps displaying land covers, curve numbers, flood zones.
Experience of User
Community
The current experience of local government is that the existing
FEMA defined floodplains and floodways are incorrect because they
are based on outdated land use/land cover estimates. Officials know
that flooding above the FEMA limits would occur with the 100-year
rainfall event, but do not have the expertise, time or funding to
easily quantify the increase in flooding extent. They are uncomfortable
making use of the existing outdated FEMA maps for decision making.
Through further discussions, the end users indicated that what would
be most useful for the decisions required of them would be to know
whether (a) proposed development is clearly subject to flooding
and building permits should be denied, (b) proposed development
is clearly not subject to flooding and permits should be granted,
or (c) proposed development is located in an area of uncertainty
where a more detailed, site-specific engineering analysis should
be required before a decision is made. This information, in the
form of a band around the line indicating the extent of flooding,
can be developed to suit the particular end user requirements of
incorporating uncertainty with respect to flood elevations or peak
discharges. The City of Columbia has not yet used the revised flood
zone information in development decision-making. They will be able
to do so once the updated peak discharges are applied to the FEMA
flood profiles and the resulting flood elevations are plotted on
a topographic map. These products will be developed and delivered
to the City early in the Synergy III effort.
Financial resources, both public and private, can be saved
if 1) detailed engineering analyses are not required for all proposed
developments near a stream, 2) flood damage is averted by identifying
and preventing development that would be subject to flooding, and
3) scientifically justifiable decision making can limit the number
and duration of lawsuits challenging the regulatory flood boundaries.
The involvement of the legal profession in storm water management
issues is a reality for the City of Columbia where local building
developers have hired an attorney to challenge land use/impervious
surface restrictions. In addition, the end users understand how
remote sensing land cover classification can improve their current
practice by providing a means to check whether an area has been
developed consistent with the planning documents used in the storm
water master plans, and whether the development within a given community
is consistent with the standard assessments of percent impervious
surfaces, for example.
Lessons
Learned
The flood zone determination project was initiated by targeting
local government as the end user. Experience on the project has
shown that consulting engineers are an additional category of end
users with their own requirements for the methodology and results
based upon their professional experience. We also learned that property
owners and builders are a separate category of end users. These
end users bring an additional requirement for accuracy and reasonableness
because of the potential for litigation. When decisions are made
that impact the use of real estate, and thus the monetary benefit
that can be derived, all methodologies and data interpretation that
could lead to the denial of development rights must be able to withstand
legal challenges. Flood zone determinations must be supported by
analyses that can identify and explain differences in the results
among FEMA floodway delineations by conventional practices and methodologies
that incorporate high-resolution remote sensing imagery.
Involving the end users in the process of identifying tools and
methodologies that support their activities and decision making
is absolutely essential. Researchers can guess at the problems facing
local governments, but can never be sure that they are working in
the right direction without cooperating with the actual end user.
Potential Activities
for Synergy III
Potential activities for Synergy III include going beyond flood
zone determination to developing more proactive strategies for management
of storm water and protection of receiving stream water quality
using high resolution remote sensing. These strategies are driven
by new federally mandated requirements from the Environmental Protection
Agency’s (EPA’s) Phase II storm water regulations that
now apply to all U.S. cities greater than 100,000 and will soon
apply to all U.S. cities with populations greater than 10,000, including
Boone County and the City of Columbia. These strategies include
the development and implementation of best management practices
(BMPs). Specific areas for control, as identified by the EPA, include
development planning on a watershed basis and the monitoring of
construction sites as small as 1 acre in size both during and after
construction.
Funding Support:
This research was funded solely by Raytheon Synergy (100%).
PROJECT PARTICIPANTS
Kathleen M. Trauth, R. Lee Peyton, Harold E. Johnson III, D. Scott
Adams, Hao Wang, Wesley B. Bolton, Aderbal C. Corrêa, Janggam
Adhityawarma
Center for Environmental Technology
Department of Civil & Environmental Engineering
University of Missouri-Columbia
|
