HomeMy WebLinkAboutMaster Plan
PLAN
Prepared for:
September 24, 2020
Prepared by:
FN ICHOLS,I NC.
4055 International Plaza, Suite 200
Fort Worth, Texas 76109
817-735-7300
PLAN
Prepared for:
09/18/2020
Prepared by:
FN ICHOLS,I NC.
4055 International Plaza, Suite 200
Fort Worth, Texas 76109
817-735-7300
STE18552
Master Drainage Plan
City of Stephenville
EXECUTIVE SUMMARY .......................................................................................................................................... 1
1.0 INTRODUCTION ............................................................................................................................................ 1
1.1 Purpose of Study and Approach ........................................................................................................ 1
2.0 EXISTING CONDITIONS ANALYSIS ....................................................................................................... 2
2.1 Data Collection .......................................................................................................................................... 2
2.2 Rain-on-Mesh Flood Modeling ........................................................................................................... 2
2.3 Identification of Project Areas ............................................................................................................ 3
3.0 MASTER PLAN DEVELOPMENT ............................................................................................................. 5
3.1 CIP Development ...................................................................................................................................... 5
3.1.1 Conceptual Storm Drain Hydraulic Analysis ....................................................................... 5
3.1.2 Methodist Branch Subbasin Hydraulic Analysis ............................................................... 9
3.1.3 Belknap Street Subbasin Hydraulic Analysis .................................................................... 10
3.1.4 Northwest Loop Subbasin Hydraulic Analysis ................................................................. 12
3.1.5 Graham Ave Culverts Hydraulic Analysis ........................................................................... 14
3.1.6 Lockhart Rd Culverts Hydraulic Analysis ........................................................................... 16
3.1.7 Swan St Culverts Hydraulic Analysis .................................................................................... 17
3.1.8 Prairie Wind Channel Hydraulic Analysis .......................................................................... 18
3.1.9 Rowland Channel Hydraulic Analysis .................................................................................. 20
3.1.10 Spring Bouquet Drainage Improvements ........................................................................... 22
3.2 Opinion of Probable Project Costs ................................................................................................. 23
4.0 PROJECT PRIORITIZATION ................................................................................................................... 25
4.1 Identification of Ranking Criteria ................................................................................................... 25
4.2 Criteria Weighting ................................................................................................................................. 25
4.3 Project Scoring ....................................................................................................................................... 26
4.3.1 Known Flooding History ............................................................................................................ 26
4.3.2 Project Cost ...................................................................................................................................... 27
4.3.3 Modeled Structure Flooding .................................................................................................... 27
4.3.4 Road Overtopping ......................................................................................................................... 28
4.4 Project Ranking ...................................................................................................................................... 28
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Figure 1: Existing Roadway and Inlets on Belknap St .................................................................. 11
Figure 2: Existing Culverts under Northwest Loop ...................................................................... 13
Figure 3: Existing Culverts at Graham Ave ................................................................................... 15
Figure 4: Existing Crossing at Lockhart Rd ................................................................................... 16
Figure 5: Example of Cross Vane Drop Structure......................................................................... 18
Figure 6: Topography Profile at Prairie Wind Channel ................................................................ 19
Figure 7: Existing Culverts at Walgreens Parking Lot ................................................................... 21
Figure 8: Existing Street and Inlets at Intersection of Midnight Shadow and Spring Bouquet Rd 23
Table 1: Pairwise Evaluation ....................................................................................................... 26
APPENDICES
Exhibits
Exhibit 1 Existing Storm Drain Infrastructure Map
Exhibit 2.1 Hydraulic Results Vector Map
Exhibit 2.2 Hydraulic Results Aerial Map
Exhibit 3.1 Capital Improvements Projects: Overview Map A
Exhibit 3.2 Capital Improvements Projects: Overview Map B
Exhibit 3.3 Capital Improvements Projects: Overview Map C
Exhibit 3.4 Capital Improvements Projects: Overview Map D
Exhibit 4 Methodist Branch Subbasin Hydraulic Results Map
Exhibit 5 Belknap Subbasin Hydraulic Results Map
Exhibit 6 Northwest Loop Subbasin Hydraulic Results Map
Exhibit 7 Graham Ave Culverts Proposed CIP Map
Exhibit 8 Swan St Culverts Proposed CIP Map
Exhibit 9 Prairie Wind Blvd Proposed CIP Map
Exhibit 10 Rowland Channel CIP Map Option 1: Buyouts
Exhibit 11 Rowland Channel CIP Map Option 2: Regional Detention
ConstructionCost
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The Stephenville Master Drainage Plan was prepared to assist the City of Stephenville in evaluating
existing drainage conditions and to develop prioritized capital improvement projects (CIPs) to address
flooding concerns in the City of Stephenville. The authorized services for the Master Drainage Plan include
developing a citywide rain-on-mesh drainage model to analyze existing drainage conditions, identifying
areas impacted by flooding, developing conceptual solutions and associated cost estimates, and creating
a ranking system to prioritize the projects.
A total of 11 potential project areas were identified based on results of the rain-on-mesh modeling and
discussion with the City staff. A total of 28 individual CIPs were proposed to mitigate flooding in the project
areas during a 100-year storm in accordance with City criteria. A project cost was developed for each CIP
based on 2019 dollars. It should be noted that the proposed improvements are based on conceptual
modeling and calculations. A detailed hydrologic and hydraulic analysis should be performed during final
design to supplement the CIP analysis to ensure the recommended improvements will not cause adverse
impact upstream or downstream of the project site.
The stormwater CIPs were prioritized according to a ranking system developed by FNI. The ranking system
is based on the following ranking criteria: Known Flooding History, Project Cost, Modeled Structure
Flooding, and Road Overtopping. Criteria weighting was developed using a pairwise methodology that
compares each criterion to all other criteria to determine which category should have the most weight in
the prioritization process. The prioritization scores and rankings for each project are shown in Appendix
C. The total estimate cost of the proposed improvements is $36,810,000.
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1.0 INTRODUCTION
In September of 2018, the City of Stephenville authorized Freese and Nichols, Inc. (FNI) to provide
ster Utility Infrastructure
Management Plan, which will include a Master Drainage Plan. The authorized services for the Master
Drainage Plan include developing a citywide rain-on-mesh drainage model to analyze existing drainage
conditions, identifying areas impacted by flooding, developing conceptual solutions and associated cost
estimates, and creating a ranking system to prioritize the projects.
1.1 APPROACH
The Stephenville Master Drainage Plan was prepared to assist the City in evaluating existing drainage
conditions and to develop prioritized capital improvement projects (CIPs) to address flooding concerns in
the City of Stephenville. The Master Plan is comprised of 11 project areas that were shown to be impacted
by flooding during the analysis of existing drainage conditions. The analysis of existing conditions and
identification of potential project areas is discussed in further detail in Section 2.0 of this report.
For each identified project area, a high-level analysis was performed to develop a potential solution and
corresponding cost estimate. A total of 28 CIPs were developed for the Master Drainage Plan. The
development of solutions and cost estimates is discussed in further detail in Section 3.0 of this report.
A system to score and rank projects was developed to prioritize these CIPs according to a range of criteria.
The development of the prioritization process and CIP rankings is discussed in further detail in Section 4.0
of this report.
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2.0
The analysis of existing conditions and identification of potential projectareas involved collecting data on
existing drainage infrastructure and developing a citywide 2D rain-on-mesh model. Areas that were shown
to experience flooding based on the results of this model were identified as potential locations for
improvements.
2.1
FNI obtained available data to assist in the development of the Master Drainage Plan. A previous master
drainage plan was prepared for the City in 2001 by Carter and Burgess, Inc. This previous study identified
areas known to experience flooding problems and proposed solutions to those problems. This study was
reviewed by FNI. Geographical Information System (GIS) data and as-builts
from previous projects were also provided to FNI by the City. It should be noted that City records are
currently incomplete and do not reflect all drainage infrastructure. To supplement the information
provided by the City, FNI acquired and studied drainage plans from the Texas Department of
Transportation (TxDOT) that documented stormwater systems within the City. Additionally, Light
Detection and Ranging (LiDAR) terrain was developed from data obtained from the Texas Natural
Resources Information System (TNRIS). The existing stormwater infrastructure identified from this data
collection is shown in Exhibit 1.
2.2 RAIN-ON-MESHMODELING
The Hydrologic Engineering Center (HEC) River Analysis System (RAS) program version 5.0.7. was used to
develop a 2D rain-on-mesh model of the City to identify areas of flooding concern. This type of model
represents the watershed as a grid of model mesh elements. Rainfall is applied to the mesh elements and
then dynamically routed between elements to simulate runoff. The mesh elements for the 2D area were
generated using a 100-foot cell size over the entire watershed. The model area does not include runoff
from areas outside the city and therefore does not indicate the entire flood risk for these sources, namely
the Bosque River.
A terrain representing existing conditions was developed for the watershed using LiDAR. Existing storm
drain systems were not included in the terrain, but significant drainage structures such as culvert crossings
were added manually to allow for a representation of existing conveyance. 2D area break lines are used
to generate mesh cells that align with designated lines and can provide more accurate definition to the
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mesh at critical areas. For this model, break lines were implemented at roadway centerlines to capture
roughness values for the -value of 0.05 was used for the watershed,
with an n-value of 0.02 for roadways and an n-value of 0.013 for culverts. The boundary condition for the
2D flow area was set to Normal Depth.
Rainfall and unit runoff for the model was generated using the Hydrologic Engineering Center (HEC)
Hydrologic Modeling System (HMS) program version 4.3. The HEC-HMS model was used to generate a
basin-averaged excess precipitation hydrograph, which represents the rainfall in the watershed after
initial losses have been accounted for. This hydrograph was used as the precipitation input for the
hydraulic model.
The rainfall input for the HEC-HMS model was obtained from the ź{a ĻĭŷƓźĭğƌ ağƓǒğƌ for the 10-, 25-
, and 100-year storm events to generate 24-hour hyetographs, which are graphical representations of the
distribution of rainfall over time. The Soil Conservation Service (SCS) curve number method was used to
compute rainfall losses based on an overall average curve number for the model area. The curve number
was generated based on Natural Resources Conservation Service (NRCS) soil data and North Central Texas
Council of Governments (NCTCOG) 2015 land use data. An overall curve number of 85 was computed for
the watershed. Arbitrary values for area and time of concentration were used in the HEC-HMS model, as
these inputs do not affect the excess precipitation hydrograph and no other output was required for the
analysis.
Simulations were executed for the 10-, 25-, and 100-year storm events. The 100-year inundation results
are shown in Exhibits 2.1 and 2.2.
2.3
A total of 27 subbasins were delineated within the City of Stephenville for the purpose of dividing the
watershed into potential project areas. The inundation depth results from HEC-RAS were used to evaluate
the impact of flooding on structures and roadways within the subbasins. For each potential project area,
the number of roads experiencing inundation depths over 2 feet along with the number of structures
experiencing inundation depths over 6 inches were counted. Additionally, each area was evaluated to
determine if the flooding impacts were caused by local flooding or by overflow from creeks and channels.
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Based on the number of structures and roadways impacted by flooding within the subbasin, they were
designated as high, medium, low, or non-priority project areas for further investigation.
A meeting was held with City staff in April 2019 to discuss the results of the rain-on-mesh model and
determine which project areas would be selected for conceptual improvements. From the 27 subbasins,
11 potential project areas were identified and selected for the development of CIPs. The selections were
made based on the modeled flooding results and known flooding issues discussed with City staff.
In April 2019, site visits were conducted at each of the identified project areas to document existing
infrastructure. Information obtained during these site visits was discussed with City staff to confirm
observations and obtain first-hand knowledge of problems.
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3.0 MENT
3.1
A high-level analysis was performed for each project area to develop proposed improvements. The CIPs
vary in project type and size, and various methods of analysis were used to evaluate the issues in each
area. Many of the project areas were addressed by CIPs that were divided into multiple phases. Counting
the phases as individual projects, a total of 28 individual CIPs were developed. The CIPs are shown in
Exhibits 3.1-3.4.
Each CIP is summarized in a one-page document in Appendix B. It should be noted that the proposed
improvements are based on conceptual modeling and calculations. A detailed hydrologic and hydraulic
analysis should be performed during final design to supplement the CIP analysis and to ensure the
recommended improvements will not cause adverse impact upstream or downstream of the project site.
3.1.1 Conceptual Storm Drain Hydraulic Analysis
The project areas discussed in this section experience flooding due to stormwater infrastructure that is
insufficient to contain the large amounts of runoff generated by large drainage areas. Generally, the only
stormwater infrastructure available in these areas outside of the roadway is roadside ditches. Some areas
do contain existing storm drain systems, but the storm drain is significantly undersized. The lack of
capacity leads to water overtopping roadways and flowing onto private property. No additional analysis
was needed for the existing conditions, and improvements were sized using typical methods described
below. More detail for these areas is provided on the project summary sheets in Appendix B.
These project areas were analyzed using a hydraulic grade line spreadsheet developed by FNI that uses
Rational Method hydrology and calculations to size proposed storm drain systems. The
proposed systems were sized to provide a combined street and pipe capacity of a 100-year storm, as
described in the City criteria.
The calculations were performed assuming a carrying capacity in the ROW of a typical road, 30-feet in
width, of 50 cfs, which corresponds to a drainage area of approximately 11 acres. The project areas
draining to the proposed storm drain were delineated into areas not to exceed this value. It was assumed
that the ROW will have adequate capacity for a 100-year storm until these delineation points are reached,
at which point the discharge will be fully captured by the proposed storm drain before the road is
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overtopped. Inlet capacity was not evaluated as part of this analysis. Additional inlets and laterals may be
necessary at closer intervals than the proposed delineations in order to fully capture discharges.
The following projects were addressed using this method.
A. Rowland Ave / Frey St Drainage Improvements
Properties located between Rowland Ave and the adjacent channel are known to experience flooding as
a result of insufficient capacity within the ROW and the existing flumes on Rowland Ave. Under existing
conditions, water overtops Rowland Ave and flows across residential properties to reach the channel. The
flooding will be addressed by proposed storm drain systems on Frey St and Jasmine St that will collect
runoff before it reaches Rowland Ave. The proposed storm drain will continue to Rowland Ave and outfall
to the existing channel as shown in Exhibit 3.3.
B. Tarleton St / Rowland Ave Drainage Improvements Phases 1 and 2
Flooding across Linda Ln, Dale Ave, Lydia St, and Charlotte Ave occurs as a result of insufficient capacity
within the ROW and a lack of conveyance from low points at Lydia St and Charlotte Ave. Under existing
conditions, water overtops the streets and flows across residential properties. The overtopping will be
addressed by a proposed storm drain system that will extend from the existing channel adjacent to
Rowland Ave to the low point at Lydia Ave. The proposed storm drain will be installed in multiple phases
as shown in Exhibit 3.3.
Properties on Rowland Ave that are adjacent to the channel are also impacted by channel overflow. The
structural flooding of these properties is addressed in the Rowland Channel Buyouts CIP.
C. Crow St / Long St Drainage Improvements
Properties along Crow St are known to experience flooding as a result of insufficient capacity within the
ROW and a lack of conveyance from the low point on Long St. Water overtops Long St at the low point
and flows across private properties to reach Crow St. The runoff is collected by an existing ditch that runs
along Crow St, outfall of two
has been constructed at the intersection of Crow St and Devine Ave. The existing
infrastructure does not provide sufficient capacity for the runoff. When runoff reaches Crow St, the road
is overtopped and water flows across private properties towards the North Bosque River.
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Master Drainage Plan
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The flooding will be addressed by proposed storm drain systems on Long St and Crow St. The Long St
storm drain will convey water from the low point in the road to the existing ditch along Long St. The Crow
St storm drain will collect runoff before the road is overtopped and will outfall to the open space south of
Crow St. The layout of the proposed storm drain is shown in Exhibit 3.2.
D. Pecan St / Graham Ave Drainage Improvements Phases 1-5
High flow and residential flooding is known to occur throughout this project area as a result of insufficient
capacity within the ROW. Under existing conditions, water overtops the streets and flows across
residential properties to follow the natural grade to the low point at Graham Ave. The flooding will be
addressed by a proposed storm drain system to be installed in multiple phases from Ollie Ave to Columbia
Ave. The storm drain system will outfall to a proposed ditch that extends from Columbia Ave to Graham
Ave. The Graham Ave culverts are currently undergoing improvements as part of a project currently being
constructed by TXDOT. Coordination with The Fort Worth and Western Railroad will be required as the
ditch will be placed along the edge of the railroad property. The layout of the proposed storm drain is
shown in Exhibit 3.2.
E. Elm St / Graham Ave Drainage Improvements Phases 1 and 2
High flow and residential flooding is known to occur throughout this project area as a result of insufficient
capacity within the ROW. Under existing conditions, water overtops Columbia Ave and intersecting streets
and flows across private properties to follow the natural grade to the low point at Graham Ave. The
flooding will be addressed by a proposed storm drain system to be installed in multiple phases from
McCart Ave to Graham Ave. The Graham Ave culverts are currently undergoing improvements as part of
a project currently being constructed by TXDOT. The layout of the proposed storm drain is shown in Exhibit
3.2.
F. Second Ave / Alexander Rd Drainage Improvements
Properties throughout this project area are known to experience flooding as a result of insufficient
capacity within the ROW. Under existing conditions, water overtops Groesbeck St, Cage St, and
intersecting streets and flows across residential properties to follow the natural grade to Alexander Rd.
The flooding will be addressed by a proposed storm drain system consisting of storm drain lines that
extend from Alexander Rd to Lillian Ave along Swan St (Base Bid Phase), Alexander Rd to Third Ave along
Cage St (Alt 1 Phase), and Alexander Rd to Third Avenue along Groesbeck St (Alt 2 Phase), per the
construction plans for the 2020 DƩƚĻƭĬĻĭƉ bĻźŭŷĬƚƩŷƚƚķ 5ƩğźƓğŭĻ {ǤƭƷĻƒ LƒƦƩƚǝĻƒĻƓƷƭ designed by
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KSA Engineers, Inc. The Base Bid Phase of this system, which includes the storm drain extending from
Alexander Rd to Lillian Ave along Swan St, will be funded by a General Land Office (GLO) Grant and is
currently in progress. The proposed storm drain system is shown in Exhibit 3.4.
G. Hyman St / Alexander Rd Drainage Improvements
Properties throughout this project area are known to experience flooding as a result of insufficient
capacity within the ROW and existing drainage system. The project area also contains a detention pond,
but the pond does not provide sufficient detention to prevent flooding. Under existing conditions, water
overtops the detention pond as well as Hyman St and 2nd Ave. The water flows across residential
properties to follow the natural grade to Alexander Rd. The flooding will be addressed by a proposed
storm drain extending from the existing system at First Ave to Third Ave along Hyman St (Alt 3 Phase) per
the construction plans for the 2020 DƩƚĻƭĬĻĭƉ bĻźŭŷĬƚƩŷƚƚķ 5ƩğźƓğŭĻ {ǤƭƷĻƒ LƒƦƩƚǝĻƒĻƓƷƭ designed
by KSA Engineers, Inc. This proposed system does address the insufficient capacity of the existing
detention pond, which will continue to overtop. The proposed storm drain system is shown in Exhibit 3.4.
H. Lingleville Rd Drainage Improvements
Ponding at the intersection of Lingleville Rd and Graham St is known to occur as a result of the grading of
the roadway and insufficient capacity within the existing drainage system. The high elevation of the
roadway at the intersection blocks water flowing down Lingleville Rd until the roadway is eventually
overtopped. The ponding and overtopping will be addressed by a proposed storm drain system extending
from the intersection of Lingleville Rd and Graham St to the existing ditch along Lingleville Rd. The existing
ditch will undergo improvements to accommodate the increased capacity from the proposed storm drain.
the layout of the proposed storm drain is shown in Exhibit 3.2. A significant portion of this CIP will be
located within the TXDOT ROW and will require coordination with TXDOT.
I. Moonlight Tr Drainage Improvements
Flooding has been observed in properties along Moonlight Tr. Runoff in this area follows the natural
topography, and because there is no existing drainage system in place to provide conveyance, the water
flows across residential properties to Moonlight Tr. The flooding will be addressed by a proposed storm
drain system extending from the open space uphill of the affected properties to the existing channel
downstream of Moonlight Tr as shown in Exhibit 3.1.
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J. Old Hico Rd Drainage Improvements
Insufficient capacity in the existing drainage system on Old Hico Rd combined with the high elevation of
the South Loop roadway results in water backing up at the upstream end of the South Loop crossing and
flowing across commercial properties. The flooding will be addressed by a proposed storm drain system
extending from Old Hico Rd to the existing outfall north of E South Loop as shown in Exhibit 3.4.
K. Dale Ave Drainage Improvements
New development along Dale Ave will result in the need for storm drain infrastructure at the intersection
of Dale Ave and Tab St. Insufficient capacity in the existing culvert under Tab St currently results in water
backing up along Dale Ave. Without the proposed improvements, it is expected that structures
downstream of Dale Ave will experience flooding. The flooding will be addressed by a proposed storm
drain that runs along Dale Ave, crosses Tab St, and connects to the proposed four culverts crossing
Dale Ave. The culverts will outfall to the existing channel downstream of Dale Ave. The layout of the
proposed storm drain is shown in Exhibit 3.1.
3.1.2 Methodist Branch Subbasin Hydraulic Analysis
The Methodist Branch project area contains stormwater infrastructure that was installed in two phases in
2006 and 2008. The storm drain system was designed for a 10-year capacity, which does not meet City
criteria. The area still experiences flooding, especially in the portion of the watershed downstream of
Vanderbilt St. According to City staff, flooding has also been observed at the upstream end of the subbasin
north of Frey St, particularly along Lillian Ave and Chamberlain Ave.
A rain-on-mesh model was developed in Infoworks ICM 9.0 to analyze the effectiveness of the existing
storm drain system and the feasibility of improvements within the Methodist Branch project area. The
hydrology methodology for the ICM model matches the hydrology described for the HEC-RAS rain-on-
mesh analysis.
A 2D mesh was generated for the Methodist Branch project area using an existing conditions terrain with
break lines and void polygons. The terrain was developed using LiDAR. Break lines were implemented in
the model at roadways to provide definition at roads and highways. Building shapefiles were imported
into the mesh as voids to represent houses and structures that may obstruct flow.
also imported to the model -value of 0.05 was used
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for the watershed, with an n-value of 0.02 for roadways. The existing storm drain was entered in the
model as conduit links based on a review of the record drawings.
Simulations were executed for the 10-, 25-, and 100-year storm events. The100-yearinundation results
for the Methodist Branch project area are shown in Exhibit 4. It was concluded that although the existing
storm drain does not meet the 100-year criteria set by City standards, it is not economically feasible to
replace or upsize the existing system. Flooding north of Frey St between Garfield Ave and Chamberlain
Ave is caused by a lack of capacity within the ROW and can be improved by extending laterals from the
existing storm drain to the upstream neighborhood, as shown in Exhibit 4.
An HGL spreadsheet was used to analyze the proposed storm drain improvements using a similar method
as described in Section 3.1.1. The proposed storm drain will extend from the existing system at the
intersection of Frey St and Chamberlain Ave northwest to the intersection of Ash St and Cleveland Ave.
The storm drain extension will collect runoff before overtopping occurs and mitigate the flooding
observed in the residential areas between Garfield Ave and Chamberlain Ave.
3.1.3 Belknap Street Subbasin Hydraulic Analysis
The Belknap St project area is known to experience high flows during storm events. According to
observations made by City staff, the flow is thought to be confined to roadways and not impact structures.
The project area contains an existing storm drain system, but the existing system is insufficient to meet
City criteria and is likely in poor condition. An example of the existing roadway and storm inlets is shown
in Figure 1.
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Figure 1: Existing Roadway and Inlets on Belknap St
A rain-on-mesh model was developed in Infoworks ICM 9.0 to analyze the effectiveness of the existing
storm drain system and the feasibility of improvements within the Belknap St project area. The hydrology
methodology for the ICM model matches the hydrology described for the HEC-RAS rain-on-mesh analysis.
A 2D mesh was generated for the Belknap St project area using an existing conditions terrain with break
lines and void polygons. The terrain was developed using LiDAR. Break lines were implemented in the
model at roadways to provide definition at roads and highways. Building shapefiles were imported into
the mesh as voids to represent houses and structures that may obstruct flow. Manning
-value of 0.05 was used
for the watershed, with an n-value of 0.02 for roadways. The existing storm drain was entered in the
model as conduit links. There are no available records of the existing system, so the storm drain in the
model was based on assumptions and observations made on site visits.
Simulations were executed for the 10-, 25-, and 100-year storm events. The 100-year inundation results
for the Belknap Street project area are shown in Exhibit 5. The detailed modeling results show that the
flooding is less severe than what is shown in the citywide rain-on-mesh results and is generally contained
within the roadway, which matches the staff understanding of the flooding in this area. The only structural
flooding shown in the detailed model occurs at commercial structures located at the downstream part of
this system near South Floral St and East Mason St. The flooding at this location is caused by a combination
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of insufficient capacity in the outfall channel and shallow grading on Floral St that leads to a wide low
point along the commercial structures.
A CIP was developed to address the structural flooding. The CIP includes improvements to the outfall
channel to increase capacity as well as re-grading of Floral St to direct runoff towards the channel. The
proposed concrete outfall channel has a trapezoidal cross section with a top width of approximately 15
feet, a bottom width of approximately 3 feet, a depth of approximately 3 feet, and 2:1 side slopes. Due to
size constraints and the elevation of Floral St at the crossing, the channel dimensions do not include
freeboard. A buyout of nearby properties could be considered at a future date to provide additional room
for the channel. The proposed improvements to the channel will extend along the length of the
commercial properties for approximately 400 feet and then transition back to existing channel conditions.
The layout of the proposed channel is shown on Exhibit 5.
3.1.4 Northwest Loop Subbasin Hydraulic Analysis
The Northwest Loop project area experiences flooding across residential houses in the neighborhood to
the south of Northwest Loop between Mockingbird Ln and Magnolia Dr. The runoff from this
neighborhood is intended to be conveyed to the ditches along Northwest Loop through roadways and a
The existing arch pipes underneath
Northwest Loop are shown in Figure 2.
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Master Drainage Plan
City of Stephenville
Figure 2: Existing Culverts under Northwest Loop
A rain-on-mesh model was developed in Infoworks ICM 9.0 to analyze the effectiveness of the existing
storm drain system and the feasibility of improvements within the Northwest Loop project area. The
hydrology methodology for the ICM model matches the hydrology described for the HEC-RAS rain-on-
mesh analysis.
A 2D mesh was generated for the Northwest Loop project area using an existing conditions terrain with
break lines and void polygons. The terrain was developed using LiDAR. Break lines were implemented in
the model at roadways throughout the City to provide definition at roads and highways. Building
shapefiles were imported into the mesh as voids to represent houses and structures that may obstruct
flow.
-value of 0.05 was used for the watershed, with an n-value of 0.02 for roadways.
Simulations were executed for the 10-, 25-, and 100-year storm events. The 100-year inundation results
for the Northwest Loop project area are shown in Exhibit 6. As shown in the results, the flume on
Mockingbird Ln is significantly undersized and cannot contain the runoff on this street. The water overtops
the road and flows between private properties. Limited capacity of the existing arch culverts at the
intersection of Northwest Loop crossing and Magnolia Rd causes water to back up until it reaches an
elevation at which it can overtop Magnolia Rd. This backup of water contributes to the flooding seen at
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the upstream properties. The water that overtops Magnolia Rd continues to flow along Northwest Loop,
where there is not sufficient capacity to contain the runoff.
The results from the Infoworks model also show that Lingleville Rd and the channel downstream of the
Northwest Loop culverts experience overtopping. However, this overtopping does not result in structure
flooding and thus is not a priority concern.
An HGL spreadsheet was used to analyze potential storm drain improvements along Northwest Loop using
a similar method as described in Section 3.1.1. The flow results from the Infoworks model were used as
inputs for the spreadsheet.
The CIP developed for this area includes upsizing the existing culverts at the driveway north of Northwest
7 A
storm drain line will be extended from the culverts to Mockingbird Ln to capture runoff before the road
is overtopped. The downstream channel will be increased in size to give it the capacity required to contain
the additional runoff that will be conveyed by the improved culverts. The proposed earthen channel has
a trapezoidal cross section with a top width of approximately 30 feet, a bottom width of approximately 6
feet, a depth of approximately 4 feet, and 3:1 side slopes. Further impact analysis should be performed
on this area before the improvements are implemented to investigate potential downstream impacts. A
significant portion of this CIP will be located within the TXDOT ROW and will require coordination with
TXDOT.
3.1.5 Graham Ave Culverts Hydraulic Analysis
The existing crossing at Graham Avenue consists of two 63that connect downstream to a
RCP. The insufficient capacity of the drainage infrastructure along with the high elevation of the roadway
causes water upstream to accumulate until the road is eventually overtopped at a low point in the road
north of the crossing. The overtopping of the crossing causes significant flooding of upstream and
downstream properties. The existing culverts at this crossing are shown in Figure 3.
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City of Stephenville
Figure 3: Existing Culverts at Graham Ave
A rain-on-mesh model was developed in Infoworks ICM 9.0 to analyze the existing conditions at this
crossing. The hydrology methodology for the ICM model matches the hydrology described for the HEC-
RAS rain-on-mesh analysis.
A 2D mesh was generated for the Graham Ave project area using an existing conditions terrain with break
lines and void polygons. The terrain was developed using LiDAR. Break lines were implemented in the
model at roadways to provide definition at roads and highways. Building shapefiles were imported into
the mesh as voids to represent houses and structures that may obstruct flow. ions were
-value of 0.05 was used
for the watershed, with an n-value of 0.02 for roadways. Results from this analysis generally confirm the
results obtained in the initial rain-on-mesh study.
To develop proposed improvements for the crossing, a model was developed in HY-8 7.50. The input flows
for this model were obtained from the HEC-RAS rain-on-mesh results.
Ave crossing that outfall to a
proposed trapezoidal channel. The proposed earthen channel has a top width of approximately 35 feet, a
bottom width of approximately 6 feet, a depth of approximately 4 feet, and 4:1 side slopes. This channel
will replace the existing storm drain downstream of the crossing, which is undersized for the Graham Ave
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City of Stephenville
drainage area. A significant portion of this CIP will be located within the TXDOT ROW. Culvert and channel
improvements are currently being implemented as part of a project designed by TXDOT. The proposed
improvements are shown in Exhibit 7.
3.1.6 Lockhart Rd Culverts Hydraulic Analysis
The existing bridge crossing at Lockhart Road has extremely limited capacity and is expected to overtop
under any significant amount of rainfall. Commercial properties upstream of Lockhart Rd experience
flooding due to the lack of conveyance at the crossing. It is anticipated that the road might be improved
to support development in this area. The existing Lockhart Rd crossing is shown in Figure 4.
Figure 4: Existing Crossing at Lockhart Rd
A model was developed in HY-8 7.50 to analyze existing conditions and develop conceptual proposed
improvements for the culverts at Lockhart Road. The input flows for this model were obtained from the
HEC-RAS rain-on-mesh results.
at the Lockhart Road crossing. These
improvements are considered conceptual and assume that in the future the road will be improved and
raised to a higher elevation. It is not possible to construct the culvert improvements without
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improvements to the road. The CIP will need to be re-evaluated in the future with the proposed roadway.
Improvements to the roadway are not included in the CIP cost estimate.
3.1.7 Swan St Culverts Hydraulic Analysis
A swale and ditch in the open area upstream of Swan St carries water through the West End Cemetery to
the Swan St road crossing. Swan St has no culverts, and the flow is forced to overtop the road. The
upstream ditch experiences significant erosion due to large flows. Portions of the ditch with steep slopes
are especially at risk of erosion due to increased velocity and energy of the flow. The ditch does not have
sufficient protection against the high energies, and headcuts have formed at these locations. Because of
the erosion and the overtopping of the road, this area was identified by City staff as in need of
improvements.
A model was developed in HY-8 7.50 to analyze existing conditions and develop conceptual proposed
improvements for the culverts at Swan Street. The input flows for this model were computed using
Rational Method calculations.
The proposed improvements consist of three 54Swan Street crossing and a proposed
downstream ditch to provide grading for the culverts. The proposed ditch will have a top width of
approximately 23 feet, a bottom width of approximately 5 feet, a height of approximately 3 feet, and 3:1
side slopes. The CIP assumes that the roadway will not be undergoing any improvements in addition to
the proposed culverts.
Cross vane drop structures are proposed to provide erosion control for the ditch. These structures protect
against erosion and work to dissipate excess energy by directing flow towards the center of the ditch and
away from the banks. The structures also provide grade control and will allow a shallow slope to be
maintained along the ditch. The placement of these structures and the proposed grading is shown in
Exhibit 8. An example of a cross vane drop structure is shown in Figure 5. Cross vane drop structures can
be used to control erosion while maintaining a natural look. Depending on the desired aesthetic for the
ditch, the structures may alternatively be constructed as concrete control matting chutes (e.g. flexamat).
This option would provide similar erosion protection but give the ditch a man-made appearance.
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Master Drainage Plan
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Figure 5: Example of Cross Vane Drop Structure
Detention areas could be incorporated into the Swan St Improvements if desired by the City. Potential
th
locations for detention include the open space along the intersection of Swan St and 6 Ave upstream of
the Swan St crossing and the open space east of the proposed grading improvements downstream of the
Swan St crossing. Requirements for detention in this area were not investigated as part of this analysis at
this time.
The improvements described in this section may be incorporated into a project funded in part by Tarleton
State University (TSU) to mitigate drainage impacts caused by future TSU development. Pacheco Koch is
currently in discussion with the City and FNI regarding the design of drainage improvements from
Washington St to Swan St.
3.1.8 Prairie Wind Channel Hydraulic Analysis
Artificial grading of the Tributary to North Bosque River, referred to here as the Prairie Wind channel, has
moved the channel away from the natural low point. Runoff that drains to the natural low point is blocked
from reaching the artificial channel and is forced to flow between residential properties and toward Blue
Jay Dr. Limited conveyance is provided in the form of small swales that connect the natural low point to
the artificial channel, but the swales do not provide adequate capacity to fully convey the runoff and
prevent structural flooding.
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A 2D rain-on-mesh model was developed in HEC-RAS 5.0.7 to analyze existing conditions and conceptual
proposed improvements at the Prairie Wind channel. Inputs for this model were the same inputs
described for the existing conditions HEC-RAS model.
It was determined that to resolve the structural flooding, a channel was needed to run behind the
residences and provide conveyance to the main Prairie Wind Channel. These improvements are part of
the Prairie Wind Channel Improvements CIP. The proposed side channel has a trapezoidal cross section
with a top width of approximately 70 feet, a bottom width of approximately 35 feet, a depth of
approximately 4 feet, and 4:1 side slopes. The proposed grading improvements and inundation results are
shown in Exhibit 9. A profile comparing the existing and proposed topography is shown in Figure 6.
Figure 6: Topography Profile at Prairie Wind Channel
The Prairie Wind crossing downstream of the channel is known to experience overtopping due to
undersized culverts and insufficient capacity in the downstream channel. Improvements to the channel
upstream of the crossing will alleviate structural flooding concerns but will not reduce overtopping at the
road. The Prairie Wind Culvert and Outfall Improvements CIP was developed to address improvements in
the roadway and downstream channel. The existing three
replaced with five Due to the large amount
of flow at this crossing, the improvements provide less than a 10-year capacity at the crossing. In order to
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achieve a 10-year capacity, which is the lowest frequency storm represented in the modeling performed
by FNI, the crossing would requirculverts. Improvements of this magnitude are not
considered economically feasible. It is recommended that a cost-benefit analysis be conducted in further
detail to determine the optimum level of improvements at this location.
The Prairie Wind Culvert and Outfall Improvements will also include channel improvements to be
implemented downstream of the crossing and will extend along a direct path to the North Bosque River.
The proposed earthen channel was designed to match the capacity of the existing culverts and has a top
width of approximately 64 feet, a bottom width of approximately 34 feet, a depth of approximately 5 feet,
and 3:1 side slopes. The proposed culverts and a portion of the proposed channel are shown in Exhibit 9.
The Prairie Wind Channel Improvements and Prairie Wind Culvert and Outfall Improvements are
considered separate projects and may be constructed independently.
3.1.9 Rowland Channel Hydraulic Analysis
The combined factors of a lack of capacity in the Rowland channel and a lack of sufficient conveyance in
the culverts downstream of Rowland channel result in the channel overflowing and flooding the
residential properties adjacent to the channel.
A steady 1D model was developed in HEC-RAS 5.0.7 to analyze existing and conceptual proposed
improvements at the Rowland Avenue channel. Inputs for this model were the same inputs described for
the HEC-RAS rain-on-mesh flood model.
The existing crossings at the Rowland channel include six 1.753 Brenda St at the upstream
Analysis of the
existing conditions model determined that the residential flooding along the channel is due to insufficient
capacity in the downstream culverts underneath the Walgreens and Washington St. As flow increases and
cannot pass through the culverts, water overtops the channel and flows across private properties. The
upstream culverts do not contribute to residential flooding. The existing culverts at the Walgreens parking
lot are shown in Figure 7.
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Figure 7: Existing Culverts at Walgreens Parking Lot
Potential improvements to the culverts and channel were analyzed in HEC-RAS. Through analysis of
different improvement scenarios, it was determined that in order to provide sufficient capacity, the
culverts underneath the Walgreens parking lot as well as the culverts at Washington St would need to be
significantly improved. This would require improvements to Washington St and likely the removal and
replacement of the Walgreens parking lot. It was also determined that it is not feasible to resolve the
structural flooding concerns through channel improvements without these significant improvements to
the culverts.
It was concluded that there is not a feasible solution involving channel improvements to resolve the
flooding issues caused by insufficient capacity of the culverts at the downstream end of the channel. Two
CIP options were developed for alternative ways to address the structural flooding seen in this area.
The first option for the Rowland Channel Improvements CIP is for the City to buy out the properties
impacted by flooding. It was assumed that properties are impacted by flooding if they are within the flood
zone generated in HEC-RAS. More detailed modeling and records of finished floor elevations will be
required to determine the magnitude of flooding at the properties with greater accuracy. The homes
recommended for buyouts along with the hydraulic results are shown in Exhibit 10. Alternatively, the City
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could buyout only the properties most frequently impacted by flooding as determined by a more detailed
analysis.
The cost estimate for this CIP was developed by obtaining the appraised value for affecting values and
adding a 30% increase to estimate the fair market value. An additional 30% contingency was added to the
total cost, as well as a 15% cost item to account for the administration effort of managing the buyouts.
The second option for the Rowland Channel Improvements CIP was developed after discussion with the
City staff and involves implementing regional detention upstream of the flooded properties. This option
would potentially involve constructing manmade wetlands and could provide water quality and education
benefits. The City could potentially partner with schools in the area to fund construction of the project.
The required volume of the detention pond is approximately 128,000 cubic yards, and an approximate
area is shown in Exhibit 11. Land acquisition needs for the detention ponds are not addressed in the CIP
and will need to be addressed as part of future planning.
3.1.10 Spring Bouquet Drainage Improvements
The flooding issues observed in the Spring Bouquet project area have been analyzed during the
development of the Spring Bouquet Drainage Improvements project, which is currently at 90% design.
The roadways in this area do not follow the natural topography, and when water overtops the road it
flows between private properties to reach the low point. The existing storm drain system in this area is
not sufficient to capture the runoff before it overtops the road.
The proposed storm drain system developed for the Spring Bouquet Drainage Improvements project has
been upsized to a 5
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City of Stephenville
Figure 8: Existing Street and Inlets at Intersection of Midnight Shadow and Spring Bouquet Rd
3.2
An opinion of probable project cost was developed for each CIP. It was assumed that larger projects would
be broken into multiple phases to achieve phases with a maximum cost of approximately $2 million.
The cost estimates include assumed utility and paving improvements based on the size and length of the
proposed storm drain improvements. For storm drain segments with widths of more than 48 inches, it
was assumed that the full width of the street will be replaced along with any water and wastewater lines.
For storm drain segments with widths of 48 inches or less, it was assumed that pavement would only be
replaced along the width of the pipe with a 2.5-foot clearance on each side. The utility improvement costs
for these segments was assumed to include only utility service replacement.
The cost estimates also include assumed quantities for inlets, laterals, and manholes. It was assumed that
a lateral connecting to a 10-foot inlet would be included for every 100 feet of pipe and that a storm drain
manhole would be included for every 700 feet of pipe, with an additional manhole at the beginning of the
line.
projects with similar design and construction elements. Due to the conceptual nature of the proposed
solutions and cost estimates, a 30% contingency and a 15% engineering cost was included in each
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estimate. It should be noted that the engineering fee is not known at this time and will vary depending on
the services required to complete the project. Appendix B contains
project cost for each CIP.
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City of Stephenville
4.0
The stormwater CIPs developed were prioritized according to a ranking system developed by FNI through
coordination with the City. The ranking system was used to assess the relative severity of the identified
drainage issues using weighted criteria that is used to assign a score to each project. The CIP ranking will
assist the City in distinguishing between projects of various priorities and determining which projects will
CIP budget.
4.1
The first step in the ranking process was to develop the criteria for scoring and ranking the projects. FNI
coordinated with the City to develop the following ranking criteria: Known Flooding History, Project Cost,
Modeled Structure Flooding, and Road Overtopping. A brief explanation of each of the criteria is provided
in the sections below.
4.2
The second step in the ranking process was to assign weighting factors to each criterion. This was
accomplished through the Pairwise process. Pairwise comparison provides a simple, customizable, and
rational framework to structure the ranking process. FNI created a Pairwise comparison table, which
allows the criteria to be weighed against each other. Table 1 shows the results of the comparison. Each
criterion was ranked against the others using a scale of 1 to 3. A score of 3 means that the criteria being
considered is determined to be more important than the criteria it is being compared to, a score of 2
means that the criteria are of the same importance, and a score of 1 means that the criteria being
considered is determined to be less important than the criteria it is being compared to. The sum of scores
for each criterion is considered its weight.
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Table 1: Pairwise Evaluation
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2 Project Cost 2 2 3 7
Modeled Structure
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Flooding
4 Road Overtopping 1 1 1 3
4.3
After the criteria weighting was complete, FNI developed descriptions and scoring systems for each
category. The goal was to establish measures that provide consistent results and allow for a
comprehensive comparison of all the CIPs. Each criterion was given a scoring range with a minimum score
of 0 to a maximum score of 10.
The following sections provide descriptions of the scoring developed for each criterion.
4.3.1 Known Flooding History
This category is used to account for areas where flooding is known to occur. This category was given the
most weight because it includes flooding that has been observed and is known to impact structures and
roadways to varying degrees. Each project was assigned a degree of known flooding based on descriptions
of existing conditions provided by staff at the City. No additional records were available to describe the
state of existing flooding. Areas that were determined to have a higher degree of flooding were given
more points in this category. The designation of each project area as Major, Minor, or Unknown is
subjective and based on input from the City staff.
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Master Drainage Plan
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Degree of Known Flooding Points
Major 10
Minor 6
None / Unknown0
4.3.2 Project Cost
This category is used to account for the cost of each project. Project cost was given a high weight because
lower-cost projects can be accomplished with less impact to the City budget and are more likely to be
feasible candidates for construction. Points in this category were given based on the estimated project
cost developed by FNI, with lower-cost projects receiving more points.
Project Cost Points
Less Than $500,000 10
Between $500,000 And $1,000,000 7
Between $1,000,000 And $1,500,000 5
Between $1,500,000 And $2,000,000 3
More Than $2,000,000 0
4.3.3 Modeled Structure Flooding
This category is used to account for structures impacted by flooding as shown in the HEC-RAS model
results. Because it is best to prevent significant damage to structures before safety becomes an issue and
costs escalate dramatically, areas with higher potential damage to structures received more points in the
category. Project scoring is based on the total number of inundated structures in the area. Structures were
elevation and were considered
inundated when the HEC-RAS depths overlapping the structure rose above this assumed FFE.
# Inundated Structures Points
More Than 5 10
Between 3 And 5 6
Less Than 3 4
None 0
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4.3.4 Road Overtopping
This category is used to account for roads that are overtopped during flooding events as shown in the
HEC-RAS model results. Because it is best to prevent roadways from overtopping and creating hazardous
conditions, areas with higher inundation within the roadways received more points in this category.
Project scoring is based on the maximum HEC-RAS inundation depth observed within roadways.
Maximum Inundation Depth Points
More Than 2' 10
5
Less Than 2
No Inundation 0
4.4
Each project was scored in each of the above criteria and then multiplied by the corresponding criteria
weights to develop a total score. The projects were then ranked according to the total score, with 240
being the maximum possible score and 0 being the lowest possible score. The projects were subjectively
categorized into short, intermediate, and long-term projects based on the scoring and discussion with the
City. Short term projects are projects that should be considered higher priority, while long term projects
are considered lower priority. The final scoring, ranking, and categorization of each CIP is summarized in
Appendix C.
28
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CITY OF STEPHENVILLE
EXHIBIT 8
SWAN ST CULVERTS
PROPOSED CIP
LEGEND
Grade Control Structure
1 Foot Contours
Proposed Culverts
Proposed Grading
Proposed Riprap
Grade Control Structure
(3) 5'x4' RCB
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SCALE IN FEET
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11/19/2019
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