Better Defining Flood Risks Spring 2012 Texas Floodplain … 2011 Ebb and Flow.pdf · Emergency...
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Upcoming Events Spring 2012 Texas Floodplain Managers Association Meeting April 3-6 ......... Corpus Christi Spring 2012 American Society of Civil Engineers Meeting April 18-21 ......... San Antonio 2012 Association of State Floodplain Managers Conference National Conference May 20-25 ........... San Antonio FALL 2011 FALL 2011 01 Continued on Page 2 Better Defining Flood Risks Through Hydrologic Calibration on Lower Marys Creek Having current, well-defined Hydrologic and Hydraulic (H/H) model calibraons is beneficial when accurately represenng floodplains and esmang realisc flooding risks of the roads and properes located along streams. Freese and Nichols, Inc. (FNI) recently performed an open channel study of Lower Marys Creek and provided updated H/H models and inundaon maps to more accurately illustrate the floodplain. The following paragraphs discuss the details and benefits of our work. Project Background Marys Creek has a 55.2 square-mile drainage area in Fort Worth and Benbrook, Texas and is the largest contributor to the Trinity River Clear Fork, downstream of Benbrook Dam. Changes in the discharges from Marys Creek directly affect the Clear Fork. The effecve Federal Emergency Management Agency (FEMA) hydrology for Marys Creek was developed by the U.S. Army Corps of Engineers (USACE), using their hydrologic modeling soſtware, SWFHYD, in the early 1980s. The model used the inial and constant loss method and the Snyder’s unit hydrograph. The effecve FEMA hydraulic model for Marys Creek was also developed by the USACE-Fort Worth District using HEC-2 in the early 1980s. New Hydrologic Model and Results FNI collected calibrated rainfall and observed stage and discharges at the U.S. Geological Survey gage on Vickery Boulevard for three storm events. We used this informaon to create a new calibrated hydrologic model using HEC-HMS (Hydrologic Modeling System) Version 3.5. We evaluated two methodologies for infiltraon losses and unit hydrographs. The first used inial and constant losses and the Snyder’s unit hydrograph; and the second used the U.S. Soil Conservaon Service (SCS) curve number method and the SCS unit hydrograph. We performed this comparison to select the most appropriate methodology to model the Marys Creek watershed. We LAST ISSUE BEFORE BLOG TRANSITION In January 2012, Ebb and Flow will transion to a blog that will be hosted on Freese.com. We will email all current subscribers with a request to add you to our blog’s RSS feed for more immediate news, updates and informaon from Ebb and Flow.
Transcript of Better Defining Flood Risks Spring 2012 Texas Floodplain … 2011 Ebb and Flow.pdf · Emergency...
Upc
omin
g Ev
ents Spring 2012 Texas
Floodplain Managers Association Meeting
April 3-6 ......... Corpus Christi
Spring 2012 American Society of Civil Engineers MeetingApril 18-21 ......... San Antonio
2012 Association of State Floodplain Managers Conference National ConferenceMay 20-25 ........... San Antonio
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Continued on Page 2
Better Defining Flood Risks Through Hydrologic Calibration on Lower Marys CreekHaving current, well-defined Hydrologic and Hydraulic (H/H) model calibrations is beneficial when accurately representing floodplains and estimating realistic flooding risks of the roads and properties located along streams. Freese and Nichols, Inc. (FNI) recently performed an open channel study of Lower Marys Creek and provided updated H/H models and inundation maps to more accurately illustrate the floodplain. The following paragraphs discuss the details and benefits of our work.
Project BackgroundMarys Creek has a 55.2 square-mile drainage area in Fort Worth and Benbrook, Texas and is the largest contributor to the Trinity River Clear Fork, downstream of Benbrook Dam. Changes in the discharges from Marys Creek directly affect the Clear Fork. The effective Federal Emergency Management Agency (FEMA) hydrology for Marys Creek was developed by the U.S. Army Corps of Engineers (USACE), using their hydrologic modeling software, SWFHYD, in the early 1980s. The model used the initial and constant loss method and the Snyder’s unit hydrograph. The effective FEMA hydraulic model for Marys Creek was also developed by the USACE-Fort Worth District using HEC-2 in the early 1980s.
New Hydrologic Model and ResultsFNI collected calibrated rainfall and observed stage and discharges at the U.S. Geological Survey gage on Vickery Boulevard for three storm events. We used this information to create a new calibrated hydrologic model using HEC-HMS (Hydrologic Modeling System) Version 3.5. We evaluated two methodologies for infiltration losses and unit hydrographs. The first used initial and constant losses and the Snyder’s unit hydrograph; and the second used the U.S. Soil Conservation Service (SCS) curve number method and the SCS unit hydrograph. We performed this comparison to select the most appropriate methodology to model the Marys Creek watershed. We
LAST ISSUE BEFORE BLOG TRANSITION
In January 2012, Ebb and Flow will transition to a blog that will be hosted on Freese.com. We will email all current subscribers with a request to add you to our blog’s RSS feed for more immediate news, updates and information from Ebb and Flow.
found the first set of methodologies to better match the response of Marys Creek. Our results for existing conditions show that discharges for the calibrated 100-year event were approximately 25 percent lower than those listed in the FIS, as shown in Table 1. We then used the calibrated hydrologic model for the flow data in the new hydraulic model.
New Hydraulic ModelWe created a new unsteady-flow HEC-RAS (River Analysis System) model to better represent the existing flooding potential of Marys Creek. We based this model on surveyed cross sections in the main channel and 2009 Light Detection And Ranging data for the overbanks. The model also takes advantage of features not available in HEC-2, such as lateral structures to represent diversions, inline structures to represent channel dams, and storage areas to represent ponds. The resulting base flood elevations were between two and seven feet lower than values listed in the FIS, removing approximately 900 structures from the existing floodplain. A comparison of the existing floodplain before and after the revised analysis is shown in Figure 1. In addition, the floodway was approximately 70 percent narrower compared to the effective floodway.
OLD HEARNE RD
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Stream flow line
Halff 100-yr floodplain
2D limits
2D depth0 - 0.5'
0.5 - 1'
1 - 1.5'
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Existing Conditions (100-yr)Still Creek Watershed Study
Bryan, Texas
0 15075Feet
4055 International Plaza, Suite 200Fort Worth, Texas 76109-4895
p: (817) 735-7300 f: (817) 735-7491
H:\STORMWATER\FINAL_EXHIBITS\InfoworksOutput.mxd
Verbal Scale: 1" = 150'Absolute Scale: 1 = 1,800
Date: May 2011Job No.: BRY10455
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Location Drainage Area (mi2)
100-Year Discharge (cfs) Difference (%)FIS FNI
1,200 feet upstream of U.S. Route 80
25.01 30,000 23,700 -21%
3,000 feet upstream of Chapin School
35.54 40,400 30,230 -25%
0.95 miles downstream of loop 820
41.98 38,100 29,660 -22%
At Old Benbrook Road (USGS gage)
54.03 43,400 32,450 -25%
Project SpotlightStill Creek Watershed Study, City of Bryan Still Creek has a history of flooding problems with a dozen homes experiencing flooding in a two-year event. Due to the complex nature of the flooding, FNI developed a 2-D model using Infoworks SD to obtain a comprehensive understanding of the existing flooding problems. Proposed alternatives are focused on regional detention basins that solve the flooding problem without moving it downstream. The project has included three public meetings to obtain resident input and is funded by a Flood Protection Planning Grant administered by the Texas Water Development Board.
Hector Olmos, P.E., CFMHector is a Storm Water Engineer and Project Manager in FNI’s Dallas office. He specializes in small- and large-scale H/H modeling, and his background includes basin-wide master plans, dam breach analyses and Emergency Action Plans, Probable Maximum Flood development, and model calibration. Hector may be reached at 817-735-7356 or [email protected]
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Figure 1: Comparison of Existing and Revised 100-Year Floodplains
Table 1: Comparison of 100-year Discharges
Storm Water Utility Tune-Ups:Review your utility, address your findings, and implement processes to minimize the potential for the variances to occur.Many cities have had storm water utilities in place for several years now. Over time, the potential for storm water utility billing discrepancies increases as new development occurs, properties redevelop, and ownership changes for other properties. In an informal survey of several cities, we noted an under-collection of revenue ranging from 5 to 25 percent overall. We also noted numerous instances of individual properties being overcharged, which leads to potential reimbursement claims. Routine billing reviews are recommended to make sure the proper fee is being assessed to rate payers. In Texas, storm water utilities are enabled, and just as importantly constrained, by the Municipal Drainage Utility Systems Act.
Utility Billing ReviewThe purpose of the utility billing review is fundamentally to determine that each rate payer is being assessed the proper fee for using the public storm system. Factors evaluated include:
� Rate structure � Rate classification � Billing redundancy � Drainage-related use of funds � Accurate determination of system use (i.e., amount of impervious area)
Considering Your Approach to Potential FindingsConsider in advance your approach for your evaluation findings.
� If you discover overcharges, how far back will you reimburse account holders? � For undercharges, will you backbill or just adjust the rate going forward? � If you discover systemic errors, such as significant funds being used for services not related to drainage,
how will you address the discrepancy?
Keep Your Utility in Check with Solid Management and Continous ImprovementA snapshot review can identify utility billing problems, but implementing sound management procedures for the utility can help minimize billing issues in the future. Inadequate processes and ineffective interdepartmental coordination often lead to incorrect storm water utility fee assessments. In short, consider a complete continuous improvement cycle approach to the management of your utility.
Trey ShanksTrey is an Environmental Scientist and Project Manager in FNI’s Dallas office. Trey specializes in municipal storm water financing, permitting and policy guidance. Please contact Trey at 217-217-2221 or [email protected]
Municipalities May Be Under-Collecting Revenue by Five to 25 PercentThinking about asking Council to raise your storm water utility rates? First, consider evaluating your existing utility billing system to make sure you are appropriately capturing the revenue intended. An informal evaluation of several cities’ storm water utility revenue collection indicates that many municipalities may be under-collecting revenue by five to 25 percent.
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Need Assistance?FNI has multiple staff available to assist with developing and/or updating storm water utlility fees. CLICK HERE to contact one of our offices.
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Who
to
Call For more information about
our storm water engineering services, please contact:
DallasMike Wayts, P.E., CFM
214-217-2222
Fort WorthKelly Dillard, P.E., CFM
817-735-7313
San Antonio/AustinJay Scanlon, P.E., CFM
512-617-3115
Houston/PearlandJeff Taylor
713-600-6831
For more information about Ebb and Flow, please contact:
Ashley Sutton
817-735-7445
82nd Legislature Exempts More than 3,000 Dams from RegulationAs part of its 82nd Legislative Session, the Texas Legislature passed changes to the Texas Water Code in relation to dam safety. These changes took the form of an amendment to the Texas Commission on Environmental Quality (TCEQ) reauthorization bill. The bill was amended as underlined below:
Section 12.052Subsection (a) The commission shall make and enforce rules and orders and shall perform all other acts necessary to provide for the safe construction, maintenance, repair, and removal of dams located in this state. In performing the commission’s duties under this subsection, the commission shall identify and focus on the most hazardous dams in the state.
Subsection (b-1)The commission may enter into an agreement with an owner of a dam who is required to reevaluate the adequacy of an existing dam or spillway. The agreement may include timelines to achieve compliance with the commission’s design criteria and may authorize deferral of compliance with the criteria, as appropriate.
Subsection (e-1)The commission shall exempt an owner of a dam located on private property from meeting requirements related to dam safety if the dam meets all of the following criteria:
(1) At a maximum capacity impounds less than 500 acre-feet(2) Has a hazard classification of low or significant
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Stevens Park Golf Course Now OpenFNI developed a three-phase master plan for Coombs Creek Trail and Stevens Park Golf Course and then provided design for each phase. As part of the project, FNI evaluated soil bioengineering techniques and implemented natural and aesthetic channel stabilization solutions on Coombs Creek, such as live crib walls, live staking and riffle pool creation. All three phases of the project are now complete and Stevens Park Golf Course (15th Hole shown at right) was recently re-opened to the public.
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(3) Is located in a county with a population of less than 215,000(4) Is not located inside the corporate limits of a municipality
Subsection (e-2)Notwithstanding subsection (e-1), an owner of a dam shall comply with operation and maintenance requirements established by commission rule
Subsection (e-3)This subsection and subsections (e-1) and (e-2) expire August 31, 2015
What This Means for Hazard Classification of DamsHazard classification for dams is based on breach analyses that are used to define the potential loss of life and economic loss (public facilities, utilities, and roads) due to a dam failure. Low hazard dams are not expected to result in the loss of life and will have minimal economic impact; significant hazard dams can result in the loss of up to six lives or appreciable economic losses; high hazard dams can result in the loss of seven or more lives or excessive economic losses.
Through efforts of the Association of Dam Safety Officials, American Society of Civil Engineers, Texas Society of Professional Engineers, Texas Council of Engineering Companies and the Texas Floodplain Administration, the amendment was modified from the original language, which would have exempted approximately 72 percent of the dams monitored by TCEQ’s Dam Safety Program. TCEQ’s initial estimate of the compromise regulation is that roughly 200 significant hazard dams and 3,000 low hazard dams will be exempted.
According to representatives of the National Dam Safety Program, reducing the number of dams regulated by the TCEQ program may result in a reduction of Federal Emergency Management Agency (FEMA) National Dam Safety Program Grant Funds allocated to Texas. In FY2009 and FY2010, Texas received $526,288 from the FEMA National Dam Safety Program.
Jay Scanlon, P.E., CFMJay is an FNI Associate, Storm Water Engineer and Project Manager in FNI’s Austin office. He specializes in storm water management and water
resources engineering. He may be reached at 512-617-3115 or [email protected].
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John Wolfhope, P.E.John is an FNI Principal and Vice President and the Division Manager for FNI’s Central Region. He is also a Water Resources Project Manager
specializing in the planning, evaluation and design of dams, reservoirs, hydraulic structures and water supply systems. He may be reached at 512-617-3118 or [email protected].
FPP Grant Applications DeadlineSponsored by the Texas Water Development Board (TWDB)The TWDB has issued a request for applications for its Flood Protection Planning (FPP) Grant program. The deadline for applications is 3 p.m. on January 11, 2012. For more information on the FPP program and its funding, CLICK HERE.If you would like assistance in determining whether the FPP program is appropriate for your projects, please contact Stephanie Griffin, P.E., CFM (FNI Storm Water Funding Specialist) at [email protected] or 817-735-7353.
For More InformationCLICK HERE to visit TCEQ’s Dam Safety Program website.
Links For More Information � Institute for Sustainable Infrastructure � Rating System � Education and Training � FAQs
FNI Supports New Sustainability Ratings for Infrastructure ProjectsCharter Member of the Institute of Sustainable Infrastructure (ISI)FNI has become a charter member of the ISI. The ISI was founded in February of this year through a joint effort by the American Society of Civil Engineers (ASCE), American Public Works Assocation and American Council of Engineering Companies. Its mission is to develop, maintain and support a civil infrastructure rating system that will measure the sustainability of infrastructure projects. The rating system will be called Envision.
What is Envision?“It’s basically the engineering equivalent to the LEED Rating System in architecture,” said FNI’s Alan Hutson, P.E., who has been part of a national ASCE committee developing sustainability criteria for pipeline projects. The rating system will help engineers and clients better evaluate infrastructure projects in terms of life cycle and collateral costs instead of just initial cost. “An Envision Certified project,” said Hutson, “will be graded on how well it meets a community’s triple bottom line of economic, social and environmental needs”. ISI plans to release the Envision Rating System in the beginning of 2012.
FNI to JOIN ISI Board of DirectorsAs a charter member, FNI will be represented on ISI’s Board of Directors Advisory Council (a strategic think tank) and also the Executive Infrastructure Forum (a policy roundtable). Alan Greer, P.E. (FNI Vice President, Principal and Division Manager of North Texas Infrastructure/Facilities), and Mikel Wilkins, P.E., LEED AP (FNI Associate and Storm Water Engineer in Dallas) will lead the firm’s effort to integrate the rating system into our design development and execution by presenting Envision to discipline leaders and project managers in the firm. Several FNI employees will eventually undergo training to become ISI Certified Assessors.
According to Wilkins, the Envision Rating System is based on the Project Sustainability Management Guidelines developed by the International Federation of Consulting Engineers and expanded to include concepts included in the LEED Rating System and the Sustainable Sites Initiative. These guidelines were the basis of the FN University (FNI’s professional development program for employees and clients) “Sustainability Principles II” course developed and presented by Wilkins in late 2010. “Several (FNI) groups, including storm water and site development, have been using these guidelines to assess the overall sustainability of their projects and using it to determine how to increase sustainability of future projects,” said Wilkins.
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Mikel Wilkins, P.E., LEED [email protected]
Alan Greer, [email protected]
Alan Hutson, [email protected]
For More Information on FNI’s Involvement, Please Feel Free to Contact:
