Page 10 - Mar/April 2016 Vol.33No.7
P. 10
SHELBY COUNTY By Chris Tripplett, PE, PMP, CPESC & Trevor Cropp, PE, CFM
Making Room for the River
Just 20 miles north of Memphis, in the using current GIS, FEMA, NOAA, and stream’s performance. It was critically
city of Millington, Big Creek Drainage NRCS soils data to develop a GIS database important to use actual rainfall records to
Basin spans 155 square miles and of the Big Creek Drainage Basin. This produce design flows for a known historic
has historically experienced flooding data was input to a hydrologic model and flooding event, the May 2010 flood which
problems, courtesy of its tributary to the used to calculate basin parameters for use inundated huge portions of the U.S. Navy’s
Loosahatchie River. in generating flow values for the various Millington NSA facility and Millington,
return frequency design storms, and to itself, as well as adjacent agricultural and
Shelby County experienced millions replicate the May 2010 flood of record. residential areas of Shelby County.
of dollars in infrastructure damages after LIDAR elevation data and bathymetric
a series of severe storms in April 2011 survey data were used to update and Typically, precipitation gauges are used
and from the historic May 2010 flooding improve the current effective hydraulic to estimate the amount of rainfall in their
statewide. Nearly 345,000 customers lost model of Big Creek. watershed to simulate an historic event.
electricity and a vital connection between These gauges are sparse, and typically,
Memphis and Millington suffered flood The existing drainage basin model not located in the watershed of interest.
damage – the Raleigh-Millington Road only extended to the Tipton County line, Next-Generation Radar data provided
Bridge. The record-breaking May 2010 but during this project, it was extended high resolution precipitation data over
flood caused a levee to be overtopped into Tipton County to more effectively the entire watershed, but required a
along Millington’s Big Creek Drainage evaluate conditions near the headwaters. significant amount of processing for use in
Canal near the Naval Support Activity This model was validated against flooding a HEC-HMS hydrologic model.
base. More than 15 inches of rain fell in data from the May 2010 flood of record
parts of both Shelby and Tipton counties and used to identify current flooding Obtaining the precipitation data was
during daylight hours on May 1. The problems within the basin. The models an important task since the consultant
Naval Base experienced flooding with were then used to evaluate potential was asked to evaluate conceptual
damage to nearly every building. solutions to flooding issues, particularly improvement projects to determine their
ones which can also improve water quality performance. BWSC needed the ability
The Millington area consists of more parameters for the existing streams of the to replicate the specific storm and use
than 50 percent low-to-moderate income basin. the resulting hydrograph to evaluate the
households. The flood damage not proposed projects. The firm was able to
only displaced this population but also Historical studies of the Big Creek input the rainfall from this historic storm
disrupted their livelihood. The flooding drainage basin have been performed by into HEC-HMS using NOAA National
left emotional scars for the residents various governmental, local, and regional Weather Service NEXRAD radar rainfall
in these neighborhoods including the organizations during the past 50 years. records for the Memphis weather station
elderly, children, and minority residents In development of this project, the Client and generate the runoff from the storm
stemming from displacement, loss of opted to have a new hydrologic model to be used in the subsequent hydraulic
income, and recovery needs that are still developed for the entire Big Creek basin. modeling of Big Creek. In addition, a
unmet today. This was achieved using the industry- method available within HEC-HMS
standard Hydrologic Engineering Center called “Gridded Rainfall Method” was
After repeated flood events, Shelby - Hydrologic Modeling System software used to not only impose the recorded
County officials requested that Barge, augmented with the HEC-GeoHMS rainfall on the basin, but to distribute
Waggoner, Sumner and Cannon, Inc., geospatial hydrology toolkit. This software it both in time and spatially across the
investigate the current conditions of Big allowed BWSC to efficiently manipulate basin to reflect the movement of the
Creek and evaluate options to prevent and analyze the massive quantities of storm system as it moved throughout the
or minimize future flooding. The project GIS data for the basin and automatically Big Creek watershed. The hydrographs
team included subcontractors EnSafe, develop many of the input parameters generated at the points of interest were
Inc., to evaluate water quality, and THY, required to produce the calculated flows then digitally stored and imported
Inc., to perform a hydraulic survey. for the basin. For instance, HEC-GeoHMS directly into a HEC-RAS (River Analysis
Updated hydrologic and hydraulic models is able to analyze digital terrain data to System) model for the required hydraulic
were used to predict performance for delineate drainage paths and watershed modeling. The Big Creek Drainage Basin
various theoretical storms and for the sub-basin boundaries into a hydrologic experienced between nine and 13 total
historic May 2010 flood. These models, data structure that represents the drainage inches of rainfall over the course of two
once calibrated, evaluated the effects of network. days. As a result of this modeling effort,
proposed conceptual level improvement viable improvements were identified to
projects to help flood reduction in the Various parameters were needed for better protect Big Creek and enhance
Millington area. At Shelby County’s the HEC-HMS model to estimate the community quality of life.
request detailed proposed construction amount of direct runoff produced by any
projects were not developed. The project theoretical or historic storm imposed on It was additional flooding and damages
concluded late summer 2015. the basin and consequently the amount from the 2011 storms that qualified the
of flow to be used in evaluating the basin area for a large grant. Shelby County
BWSC’s methodology consisted of
10 TPW March/April 2016
Making Room for the River
Just 20 miles north of Memphis, in the using current GIS, FEMA, NOAA, and stream’s performance. It was critically
city of Millington, Big Creek Drainage NRCS soils data to develop a GIS database important to use actual rainfall records to
Basin spans 155 square miles and of the Big Creek Drainage Basin. This produce design flows for a known historic
has historically experienced flooding data was input to a hydrologic model and flooding event, the May 2010 flood which
problems, courtesy of its tributary to the used to calculate basin parameters for use inundated huge portions of the U.S. Navy’s
Loosahatchie River. in generating flow values for the various Millington NSA facility and Millington,
return frequency design storms, and to itself, as well as adjacent agricultural and
Shelby County experienced millions replicate the May 2010 flood of record. residential areas of Shelby County.
of dollars in infrastructure damages after LIDAR elevation data and bathymetric
a series of severe storms in April 2011 survey data were used to update and Typically, precipitation gauges are used
and from the historic May 2010 flooding improve the current effective hydraulic to estimate the amount of rainfall in their
statewide. Nearly 345,000 customers lost model of Big Creek. watershed to simulate an historic event.
electricity and a vital connection between These gauges are sparse, and typically,
Memphis and Millington suffered flood The existing drainage basin model not located in the watershed of interest.
damage – the Raleigh-Millington Road only extended to the Tipton County line, Next-Generation Radar data provided
Bridge. The record-breaking May 2010 but during this project, it was extended high resolution precipitation data over
flood caused a levee to be overtopped into Tipton County to more effectively the entire watershed, but required a
along Millington’s Big Creek Drainage evaluate conditions near the headwaters. significant amount of processing for use in
Canal near the Naval Support Activity This model was validated against flooding a HEC-HMS hydrologic model.
base. More than 15 inches of rain fell in data from the May 2010 flood of record
parts of both Shelby and Tipton counties and used to identify current flooding Obtaining the precipitation data was
during daylight hours on May 1. The problems within the basin. The models an important task since the consultant
Naval Base experienced flooding with were then used to evaluate potential was asked to evaluate conceptual
damage to nearly every building. solutions to flooding issues, particularly improvement projects to determine their
ones which can also improve water quality performance. BWSC needed the ability
The Millington area consists of more parameters for the existing streams of the to replicate the specific storm and use
than 50 percent low-to-moderate income basin. the resulting hydrograph to evaluate the
households. The flood damage not proposed projects. The firm was able to
only displaced this population but also Historical studies of the Big Creek input the rainfall from this historic storm
disrupted their livelihood. The flooding drainage basin have been performed by into HEC-HMS using NOAA National
left emotional scars for the residents various governmental, local, and regional Weather Service NEXRAD radar rainfall
in these neighborhoods including the organizations during the past 50 years. records for the Memphis weather station
elderly, children, and minority residents In development of this project, the Client and generate the runoff from the storm
stemming from displacement, loss of opted to have a new hydrologic model to be used in the subsequent hydraulic
income, and recovery needs that are still developed for the entire Big Creek basin. modeling of Big Creek. In addition, a
unmet today. This was achieved using the industry- method available within HEC-HMS
standard Hydrologic Engineering Center called “Gridded Rainfall Method” was
After repeated flood events, Shelby - Hydrologic Modeling System software used to not only impose the recorded
County officials requested that Barge, augmented with the HEC-GeoHMS rainfall on the basin, but to distribute
Waggoner, Sumner and Cannon, Inc., geospatial hydrology toolkit. This software it both in time and spatially across the
investigate the current conditions of Big allowed BWSC to efficiently manipulate basin to reflect the movement of the
Creek and evaluate options to prevent and analyze the massive quantities of storm system as it moved throughout the
or minimize future flooding. The project GIS data for the basin and automatically Big Creek watershed. The hydrographs
team included subcontractors EnSafe, develop many of the input parameters generated at the points of interest were
Inc., to evaluate water quality, and THY, required to produce the calculated flows then digitally stored and imported
Inc., to perform a hydraulic survey. for the basin. For instance, HEC-GeoHMS directly into a HEC-RAS (River Analysis
Updated hydrologic and hydraulic models is able to analyze digital terrain data to System) model for the required hydraulic
were used to predict performance for delineate drainage paths and watershed modeling. The Big Creek Drainage Basin
various theoretical storms and for the sub-basin boundaries into a hydrologic experienced between nine and 13 total
historic May 2010 flood. These models, data structure that represents the drainage inches of rainfall over the course of two
once calibrated, evaluated the effects of network. days. As a result of this modeling effort,
proposed conceptual level improvement viable improvements were identified to
projects to help flood reduction in the Various parameters were needed for better protect Big Creek and enhance
Millington area. At Shelby County’s the HEC-HMS model to estimate the community quality of life.
request detailed proposed construction amount of direct runoff produced by any
projects were not developed. The project theoretical or historic storm imposed on It was additional flooding and damages
concluded late summer 2015. the basin and consequently the amount from the 2011 storms that qualified the
of flow to be used in evaluating the basin area for a large grant. Shelby County
BWSC’s methodology consisted of
10 TPW March/April 2016
