Division of Water
Indiana Department of Natural Resources
Hydraulic Modeling Checklist Supporting Documents
Table of Contents
1.0 General Project Information ................................................................................................................... 3
1.1 Stream Topographical Survey ............................................................................................................. 3
1.2 Stream Characteristics ........................................................................................................................ 3
2.0 Hydraulic Analysis ................................................................................................................................... 3
2.1 Duplicate Effective Model ................................................................................................................... 3
2.2 Corrected Effective Model .................................................................................................................. 4
2.3 Proposed Conditions Model ............................................................................................................... 5
3.0 Modeling Results..................................................................................................................................... 5
Appendix A: FIS Map/Profile ....................................................................................................................... 10
Appendix B: Check-RAS Output .................................................................................................................. 10
Appendix C: Cross Section Plots .................................................................................................................. 10
Appendix D: Profile Plots ............................................................................................................................ 10
1.0 General Project Information
This hydraulic report is for a proposed pedestrian structure in Ravina Park over Bowman Creek
in South Bend, St. Joseph County, Indiana. The proposed structure will replace an existing failed
culvert. The proposed structure is approximately 2375 feet upstream of the mouth of Bowman
Creek (discharge into the St. Joseph River). This project is part of a Senior Design course at the
University of Notre Dame and has been completed by Senior undergraduate civil engineering
majors with the assistance of the South Bend City Engineer.
The proposed structure is a 16 foot Conspan concrete arch with a 5’-10” rise. The proposed high
chord elevation of the structure is 709 feet. The bridge width will be approximately 9’-4.5” to
accommodate pedestrian and bike traffic only.
1.1 Stream Topographical Survey
A topographical survey of the proposed bridge site was performed by Jones Petrie Rafinski on
February 28, 2014. This survey provided cross sections of the proposed bridge only, while all
other cross sections in the model were from the existing HEC-2 model.
1.2 Stream Characteristics
All stream data corresponds to the published Flood Insurance Study for St. Joseph County and
the original HEC-2 model. The FIS regulatory flow rates for the 10 year, 50 year, 100 year, and
500 year flood events are 615 cfs, 830 cfs, 925 cfs, and 1120 cfs respectively. These flow rates
correspond to the flow rate at the farthest upstream reach and the flow is constant the entire
length of the creek.
2.0 Hydraulic Analysis
A hydraulic analysis of Bowman Creek was performed to determine the effect of the proposed
structure on the water surface elevations of the creek. The baseline model used for this analysis
was the 1988 HEC-2 model of Bowman Creek used in the published St. Joseph County Flood
Insurance Study, obtained from the Indiana Department of Natural Resources Hydrology and
Hydraulics Modeling Library. All flow data in this model was verified as matching the current
FIS flow rates. In addition, it was confirmed that there had been no new permits for structures on
the creek since the 1988 model. This HEC-2 model was updated and used as the baseline for the
subsequent HEC-RAS hydraulic models summarized in the following sections.
2.1 Duplicate Effective Model
The HEC-2 model was first converted to a usable HEC-RAS format by importing the data into
HEC-RAS v. 4.1.0. The stationing was initially changed from the HEC-2 stationing to sequential
labelling of each cross section. This was later converted to stream distance above the mouth of
the creek in feet by using the downstream reach length of each cross section. This stationing is
consistent with all subsequent versions of the model.
Due to differences in computational processes of HEC-RAS versus HEC-2, there were numerous
errors with importing the HEC-2 data, particularly around the existing structures. In the HEC-2
model, the distance between upstream cross section and deck/roadway was 0 feet for each
structure. HEC-RAS requires a positive distance, so the distance between upstream cross section
and deck/roadway was changed to 1 foot for each cross section. The downstream reach length
was adjusted accordingly by decreasing the length by 1 foot. Additionally, there were many
errors associated with the structures upstream of the proposed bridge location. To improve
accuracy and narrow the scope of the model, the model was limited to just include one structure
upstream of the proposed location and the entire downstream length of the stream. It was
assumed that the upstream structures would have no effect on the downstream water surface
elevations.
There were discrepancies between the Duplicate Effective model results and the published FIS
water surface elevations from the HEC-2 model. After consultation with Tamika Ali-Yerima, the
Engineering Section Manager in the Division of Water at the Indiana Department of Natural
Resources, it was assumed that these discrepancies were due to typical conversion errors
between HEC-2 and HEC-RAS and that the water surface elevations produced by the Duplicate
Effective model were correct.
2.2 Corrected Effective Model
The original HEC-2 model did not incorporate the existing structure at Ravina Park, so this was
added in the Corrected Effective model. For this model, the structure was assumed to be in its
original condition, i.e. spanning the entire width of the creek and with all hand rails intact. Cross
sections immediately upstream and downstream were added based on the JPR survey. Additional
cross sections from the JPR survey located at a 2:1 expansion upstream and 1:1expansion
downstream were added. The added cross sections are summarized below:




River station 2356: downstream cross section located at an approximate 1:1 expansion,
about 15 feet downstream from the existing culvert.
River station 2370: cross section 1 foot downstream from the existing culvert
River station 2380: cross section 1 foot upstream of the existing culvert
River station 2393: upstream cross section located at an approximate 2:1 expansion,
about 14 feet upstream of the existing culvert
The culvert was added at river station 2375 and was modeled as two identical 3.5 foot diameter
concrete pipe culverts. From the JPR survey, the length of the culvert was determined to be 8
feet, the invert elevation was found to be 699.82 feet and the centerline stations were found to be
at -25.06 feet and -18.56 feet. The entrance loss coefficient was assumed to be 0.2 (from Table 63 for concrete pipe with headwall and wingwalls). A standard Manning’s coefficient of 0.013
was used. All other cross section and structures were unchanged.
Ineffective flow areas were added at a 2:1 expansion upstream and 1:1 expansion downstream of
the culvert opening. The upstream ineffective flow areas were marked as permanent.
2.3 Proposed Conditions Model
The proposed Conspan concrete arch bridge was added to the Proposed Conditions model to
ensure that there is not a change of over 0.14 feet in the water surface elevation of the creek for
100 year storm events. The proposed bridge is a 16 foot Conspan concrete arch with a 5’-10”
rise. The proposed high chord elevation of the structure is 709 feet. The bridge width will be
approximately 9’-4.5” to accommodate pedestrian and bike traffic only.
All cross sections in the Proposed Conditions model are the same as in the Corrected Effective
model. The two culverts were replaced with the proposed alternative by modeling the Conspan
Arch with a 16 foot span, 5.83 foot rise, span/rise ration of approximately 2:1, and 2 45-degree
wing walls. The invert elevation, entrance loss coefficient, and Manning’s coefficient were all
unchanged from the Corrected Effective. The arch centerline was placed at -0.03 feet. Because
area around the structure will need to be filled, a deck was placed around the structure for a
conservative approximation of fill. Ineffective flow areas were again added at an approximate
2:1 expansion upstream and 1:1 expansion downstream of the arch opening, again with upstream
ineffective flow as permanent.
3.0 Modeling Results
The results of these models show that the proposed arch structure will not raise the water surface
elevation of the creek by more than the allowable 0.14 feet in the 100 year storm event. A
summary of modeling and project evaluation results for each profile is presented below in Tables
1-4.
Table 1. Summary of Modeling and Project Evaluation Results- 10 Year
LOCATION
PUBLISHED
DESCRIPTION
DATA
BASED ON Duplicate
Model
Location
FIS
Cross
Description
Effective
Section
MODELING RESULTS
COMPARISONS
Corrected Existing/Pre- Proposed/Post- Cumulative
Effective project
project model Impacts w/o
Model
Project
Cumulative
Impacts
with
Project
Table 2. Summary of Modeling and Project Evaluation Results- 50 Year
LOCATION
PUBLISHED
DESCRIPTION
DATA
BASED ON Duplicate
Model
Location
FIS
Cross
Description
Effective
Section
MODELING RESULTS
COMPARISONS
Corrected Existing/Pre- Proposed/Post- Cumulative
Effective project
project model Impacts w/o
Model
Project
Cumulative
Impacts
with
Project
Table 3. Summary of Modeling and Project Evaluation Results- 100 Year
LOCATION
PUBLISHED
DESCRIPTION
DATA
BASED ON Duplicate
Model
Location
FIS
Cross
Description
Effective
Section
MODELING RESULTS
COMPARISONS
Corrected Existing/Pre- Proposed/Post- Cumulative
Effective project
project model Impacts w/o
Model
Project
Cumulative
Impacts
with
Project
Table 4. Summary of Modeling and Project Evaluation Results- 500 Year
LOCATION
PUBLISHED
DESCRIPTION
DATA
BASED ON Duplicate
Model
Location
FIS
Cross
Description
Effective
Section
MODELING RESULTS
COMPARISONS
Corrected Existing/Pre- Proposed/Post- Cumulative
Effective project
project model Impacts w/o
Model
Project
Cumulative
Impacts
with
Project
Appendix A: FIS Map/Profile
Appendix B: Check-RAS Output
Appendix C: Cross Section Plots
Appendix D: Profile Plots