Culverts (inlet/outlet control)¶
HDAT evaluates culvert hydraulics by computing inlet control and outlet control, then taking the governing headwater ratio \(H/D\).
Combination suggestion (legacy behavior)¶
The tool can suggest culvert combinations from precomputed capacity tables keyed by:
- shape (Box / Circular)
- slope class
- \(H/D\) class
Legacy logic:
- choose the first capacity that exceeds the design discharge
- provide multiple nearest higher options
- if static capacity tables are insufficient, synthesize additional combinations dynamically
Inlet control \(H/D\) (legacy approach)¶
Let:
- \(A\): flow area
- \(D\): characteristic depth (box height \(h\) or pipe diameter \(d\))
- \(Q\): discharge
- \(cf = 1.811\)
- \(val = \frac{Q}{A\sqrt{D}}\)
Legacy regime branching:
- if \(val \le 1.93\): “unsubmerged” equation family
- if \(val \ge 2.21\): “submerged” equation family
- otherwise: interpolate between both
Interpolation:
\[
hd = \frac{(0.28-(val-1.93))\cdot hd_{1.93} + (val-1.93)\cdot hd_{2.21}}{0.28}
\]
Outlet control \(H/D\)¶
Legacy outlet control uses iterative hydraulic evaluation including:
- Manning losses
- energy terms
- regime patterns (free surface, partially full, pressurized) by geometry and slope type
Outputs include:
- \(hd_{outlet}\)
- outlet velocity
- hydraulic water level estimates
Governing headwater¶
\[
hd_{governing} = \max(hd_{inlet}, hd_{outlet})
\]
What to record for design audit¶
- selected culvert geometry and combination
- \(hd_{inlet}\), \(hd_{outlet}\), and governing value
- control type and any regime classification
- outlet velocity used for protection sizing