9. MY JOB
2) ESTIMATE PEAK FLOW MAGNITUDES
Since The Main-Channel Slope = 140.8 feet / mile > 50 feet / mile,
Burrington Brook is considered a STEEP STREAM.
10 Year Flood Peak Flow Estimation (using steep stream equation):
𝑄10 = 0.02430𝐴0.891 𝑃2.21
Knowing 𝑃 = 51.56 𝑖𝑛 and 𝐴 = 1.03 𝑚𝑖 …
𝑸 𝟏𝟎 = 𝟏𝟓𝟏. 𝟕𝟗𝟒
𝒇𝒕 𝟑
𝒔𝒆𝒄
10. MY JOB
2) ESTIMATE PEAK FLOW MAGNITUDES
Compare to 25-Year flood and 100-Year flood peak flows:
25 Year Flood Peak Flow Estimation:
𝑄25 = 0.03387𝐴0.893 𝑃2.20
𝑄25 = 203.408
𝑓𝑡3
𝑠𝑒𝑐
100 Year (Base) Flood Peak Flow Estimation:
𝑄100 = 0.05765𝐴0.897
𝑃2.15
𝑄100 = 284.307
𝑓𝑡3
𝑠𝑒𝑐
11. MY JOB
3) DETERMINE CROSS-SECTIONAL AREAS
Primary Purpose
• Water flow (Q) depends on Water Velocity (v) and Channel
Cross-Sectional Area (A)
• Cross-Sectional Area changes a great deal in a river
• Depending upon the river’s area (at any one point), we can
determine the water surface elevation
• This is important for determining the appropriate
height for the bridge
Software: Watershed Modeling System (WMS)
15. MY JOB
5) DETERMINE SCOUR DEPTH
What is Scour?
Definition: Erosion caused by swiftly moving water on the
abutments of a bridge, which could eventually threaten the
bridge’s structural integrity
3 Types of Scour: Contraction, Pier and Abutment
For this particular bridge, the bridge was short enough to not
require piers in its design. Further, the bridge opening is
appropriately sized for the brook and there is therefore no
contraction scour (the water does not have to squeeze inside a
small opening to pass under the bridge).
16. MY JOB
6) DETERMINE SCOUR DEPTH
According to the LRFD Bridge Manual (Given that Sadoga Road is Local and Rural):
i)Scour Design Flood Frequency = 25 Years
ii)Scour Check Flood Return Frequency = 50 Years
17. MY JOB
5) DETERMINE SCOUR DEPTH
MassDOT Abutment Scour Equation:
𝑌𝑠
𝑌𝑎
= 2.27𝐾1 𝐾2(
𝐿′
𝑌𝑎
)0.43 𝐹𝑟0.61
𝐾1= coefficient for abutment shape
𝐾2= coefficient for angle of embankment to flow
𝐿′
= the length of abutment projected normal to flow, (ft)
𝑌𝑎= average depth of flow in the floodplain, (ft)
𝐹𝑟= the Froude Number, 𝐹𝑟 =
𝑉𝑒
𝑔𝑌𝑎
𝑉𝑒 =
𝑄 𝑒
𝐴 𝑒
, (ft/s)
𝑄 𝑒= the flow obstructed by the abutment and approach embankments (ft3/s)
𝐴 𝑒= flow area of approach cross section blocked by embankments, (ft2)
𝑌𝑠= scour depth, (ft)
Scour Depth (𝒀 𝒔) @ 25 Years = 1.95 Feet
Scour Depth (𝒀 𝒔) @ 50 Years = 2.11 Feet
18. MY JOB
6) MAKE RECOMMENDATIONS
Recommendation #1:
Hydraulic Design Flood Return Frequency = 10 Years
19. MY JOB
6) MAKE RECOMMENDATIONS
Recommendation #2:
Peak Water Surface Elevation Directly Upstream of Bridge (10 Year Design) = 1402.02 feet
20. MY JOB
6) MAKE RECOMMENDATIONS
Scour Depth
Below Channel Floor
Recommendation #3: Scour Depth
Scour Depth (𝒀 𝒔) @ 25 Years = 1.95 Feet
Scour Depth (𝒀 𝒔) @ 50 Years = 2.11 Feet
21. HYDRAULIC REPORT OUTLINE
1. Executive Summary – Summarize the scope and significant results of the study
2. Project Description – Define the context of existing structure within the local and regional built and
natural environment. Five sections:
I. Existing Bridge
II. Crossed waterway
III. Highway conveyed
IV. Land uses in the vicinity of the bridge
V. Special site considerations
3. Data Collection – Summarize the results of the hydraulic study’s data collection
4. Engineering Methods – Identify Analytical Methods
I. Hydrologic Analyses
II. Hydraulic Analyses
III. Scour Safety/Stability Analyses
5. Conclusions and Recommendations
6. Appendices