Water Resources - IMPACT - January 2018 - 16

Figure 3 (above left). Flood inundation mapping on main stem rivers by
U.S. Army Corps of Engineers (dark blue) and elsewhere in the landscape
from the National Water Model (light blue).
Figure 4 (above right). Overlay of address points on flood inundation
mapping of the Neches River. The orange boxes shown are from the U.S.
National Grid used to direct search and rescue.

scale picture of flood inundation across
the whole impacted area, which covered
about 40,000 miles of streams and rivers in
southeast Texas.
The National Water Model has several
modes of operation-an Analysis model
that uses recent and current data to assess
conditions over the past two days up to
the present time, a Short-Term forecasting
model that looks 18 hours ahead and is
updated hourly, and a Medium-Term
forecasting model that looks 10 days ahead
and is updated every 6 hours. In all cases,
flood inundation maps were prepared for
each stream reach by looking through the
forecast or analysis period and picking out
the highest forecast discharge. Synthetic
rating curves for each stream reach were
used to convert discharge into water depth
in the stream, and then a map called Height
Above Nearest Drainage (HAND), of the
relative elevation of the surrounding land
surface above the bed of stream, was used
to determine the inundation extent. Figure
3 shows an overlay of the engineering scale
mapping on the main stem rivers done by
the U.S. Army Corps of Engineers and the
HAND-based flood mapping. A revised
version of this map was supplied to the
Governor of Texas who asked for a map
of the inundated areas in the flood
impact region.
Defining inundated areas is important
but the value of inundation mapping is
significantly enhanced if the impact of
flooding on people and infrastructure can
also be assessed. During the past year, the
Center for Water and Environment of the
University of Texas at Austin has collected
9.2 million address points from the
Emergency Communications Districts in

16 * Water Resources IMPACT

January 2018

Texas. Each home and business is located
with a point having latitude and longitude
coordinates, and these points are used
by 911 dispatchers to direct emergency
response vehicles. Figure 4 shows an
overlay of inundation mapping created
by the U.S. Army Corps of Engineers for
the Neches River with this Address Point
dataset-each address point corresponds
to approximately three people (Texas has
a population of 27 million people and 9
million address points), so by knowing
the number of inundated address points,
the size of the population impacted can
be assessed. By zooming into a particular
neighborhood (also shown in Figure 4), the
address points requiring search and rescue
can be identified-this is done on the U.S.
National Grid coordinate system employed
to direct helicopters in airborne search
and rescue.
Hurricane Harvey revealed that in
such a huge disaster it is critical to be
able to understand the overall pattern of
water inundation in the landscape as it is
now and how this is evolving with time.
Flood inundation mapping derived from
the National Water Model proved to be
an effective basis for supporting such
mapping, in cohesion with engineering
scale inundation mapping produced by
the U.S. Army Corps of Engineers for
the mainstem rivers. It must be said,
however, that yet more information than
this is needed. What is particularly critical
is the impact of flooding on the road
transportation system.
Hurricane Harvey was a "pluvial" flood
as well a "fluvial" flood-that is, significant
impacts came from the direct impact of
long-lasting precipitation on neighborhoods,

as well as inundation from streams and
rivers flowing through cities. Examining
water conditions at neighborhood scale
requires much more observational data than
is currently being collected. Extension of the
USGS data collection program, establishing
water sensors on bridge networks, and
synthesis of local water observation networks
established by cities and counties are needed.
Other, unconventional information sources
are also needed-one flood Facebook group
formed in Houston during Hurricane Harvey
had more than 150,000 members. It would be
helpful if they could contribute a description
of flood conditions in their neighborhood in
a way that could inform the National
Water Model.
The National Water Model is built on the
idea that hydrology can be like weather-
simulated and forecast everywhere, at
local scale, all the time. However, it is not
just hydrology that is needed-the spatial
pattern of water flow in streams, streets
and across the landscape is a problem of
hydraulics as well as hydrology. Hyperresolution simulation of water conditions
in local areas is needed to supplement the
National Water Model during intense storms
like Hurricane Harvey. ■
David R. Maidment is the Hussein M. Alharthy
Centennial Chair of Civil Engineering at
the University of Texas at Austin. In 2016,
he was elected to the National Academy of
Engineering for development of geographic
information systems applied to hydrologic
processes. AWRA annually bestows the David
R. Maidment Award for Water Resources Data
and Information Systems for outstanding
accomplishments in that field. Contact:
maidment@mail.utexas.edu.



Table of Contents for the Digital Edition of Water Resources - IMPACT - January 2018

President’s Message
The National Water Model Vision
Transforming NOAA Water Prediction: The New National Water Model
Perspectives on the National Water Model
FloodCast: A Framework for Enhanced Flood Event Decision Making for Transportation Resilience
Hurricane Harvey and the National Water Model
Contributions of the Academic Community in Advancing the National Water Model
Turning on the Faucet: Making National Water Model Data Flow
The New Economics of Water: Balancing Urban and Agricultural Water Needs on Colorado’s Front Range
What’s Up with Water: United We Stand, Divided We Fall: States Rights and WOTUS Rule
International Conference Recap
AWRA State Section and Student Chapter News
December JAWRA Highlights
In Memoriam: Ari Michelsen
2018-2019 Richard A. Herbert Memorial Scholarship Opportunities
AWRA Board of Directors 2018 Call for Nominations
Water Resources - IMPACT - January 2018 - Intro
Water Resources - IMPACT - January 2018 - cover1
Water Resources - IMPACT - January 2018 - cover2
Water Resources - IMPACT - January 2018 - 3
Water Resources - IMPACT - January 2018 - 4
Water Resources - IMPACT - January 2018 - President’s Message
Water Resources - IMPACT - January 2018 - The National Water Model Vision
Water Resources - IMPACT - January 2018 - 7
Water Resources - IMPACT - January 2018 - Transforming NOAA Water Prediction: The New National Water Model
Water Resources - IMPACT - January 2018 - 9
Water Resources - IMPACT - January 2018 - Perspectives on the National Water Model
Water Resources - IMPACT - January 2018 - 11
Water Resources - IMPACT - January 2018 - FloodCast: A Framework for Enhanced Flood Event Decision Making for Transportation Resilience
Water Resources - IMPACT - January 2018 - 13
Water Resources - IMPACT - January 2018 - Hurricane Harvey and the National Water Model
Water Resources - IMPACT - January 2018 - 15
Water Resources - IMPACT - January 2018 - 16
Water Resources - IMPACT - January 2018 - Contributions of the Academic Community in Advancing the National Water Model
Water Resources - IMPACT - January 2018 - 18
Water Resources - IMPACT - January 2018 - Turning on the Faucet: Making National Water Model Data Flow
Water Resources - IMPACT - January 2018 - 20
Water Resources - IMPACT - January 2018 - The New Economics of Water: Balancing Urban and Agricultural Water Needs on Colorado’s Front Range
Water Resources - IMPACT - January 2018 - What’s Up with Water: United We Stand, Divided We Fall: States Rights and WOTUS Rule
Water Resources - IMPACT - January 2018 - 23
Water Resources - IMPACT - January 2018 - 24
Water Resources - IMPACT - January 2018 - International Conference Recap
Water Resources - IMPACT - January 2018 - AWRA State Section and Student Chapter News
Water Resources - IMPACT - January 2018 - December JAWRA Highlights
Water Resources - IMPACT - January 2018 - In Memoriam: Ari Michelsen
Water Resources - IMPACT - January 2018 - 2018-2019 Richard A. Herbert Memorial Scholarship Opportunities
Water Resources - IMPACT - January 2018 - AWRA Board of Directors 2018 Call for Nominations
Water Resources - IMPACT - January 2018 - cover3
Water Resources - IMPACT - January 2018 - cover4
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