Bridge Engineering: Hydrologic and Hydraulic Analysis and Design Requirements (Vocabulary)

Vocabulary flashcards covering key terms and definitions from the Hydrologic and Hydraulic Analysis and Design Requirements notes.

OWL/NWL (Ordinary Water Level / Normal Water Level)

Height of water in the river under normal conditions.

MFL (Maximum Flood Level)

Highest recorded flood level based on community observations, to be verified by the hydrologist.

Design Flood

Discharge used to measure the capacity of the bridge for design purposes.

Design Flood Level (DFL)

The design flood level calculated from the design flood discharge; used as the reference for freeboard.

ULSF (Ultimate Limit State Flood)

The design flood against which the bridge is structurally designed to withstand the force of the water.

Check Flood

A less frequent flood with greater runoff than the design flood; may cause catastrophic effects on the bridge (per Volume 3 and AASHTO LRFD 2012).

Catchment Delineation

Process of determining the basin boundary and computing catchment area from maps or surveys (1:50,000 NAMRIA, topo/air survey) using methods such as planimeter, triangulation, cross-section paper, or CAD/GIS.

Hyetographs (Rainfall Analysis)

Design rainfall analysis represented as hyetographs for hydrological analysis of rainfall data.

Rational Formula

One method to estimate peak discharge (Q) at a location.

Flood Frequency Analysis

Method to estimate flood flows based on statistical frequency/recurrence.

Unit Hydrograph

A method to estimate the runoff hydrograph from unit rainfall.

Storage Function Method

A hydrologic method to estimate the runoff hydrograph using a storage function.

Q (Discharge)

Rate of flow in the channel; commonly used as peak discharge for design.

Q = A V

Discharge equals cross-sectional area (A) multiplied by flow velocity (V).

Backwater

Upstream water surface rise caused by obstructions or channel changes, affecting flow area and velocity.

Constriction Ratio

Ratio of the bridge waterway opening area to the obstructed waterway area.

Contraction Scour

Scour caused when flow converges toward the bridge, accelerating through a constricted section.

General Scour

Erosion of the channel bed due to flood flow, which can be short-term or long-term.

Local Scour

Scour around piers, abutments, and noses of guide banks caused by vortices.

Contraction Scour (redundant term kept for clarity)

(See Contraction Scour above.)

Pile Foundation (scour reduction options)

Strategies to reduce pier scour: fewer piers, longer spans, bullet-nosed or circular piers, drilled shafts, alignment with flood flow.

Approach Embankments (scour protection)

Embankments encroaching on floodplains that require protection from scour/erosion (riprap, vegetation, etc.).

Abutments Scour Protection

Protection measures for abutments against scour: vertical walls, sheet pile toe walls, riprap, rock gabions/mattresses, concrete facing to one-year flood level.

Riprap

Rock protection used to shield bridge abutments and slopes from scour.

Guide Banks

Structures used to align flood flow with the waterway and minimize scour; viable when floodwater travels along the approach embankment for more than about 240 m.

Downstream Influences

Effects such as backwater from downstream lakes, rivers, or seas that must be considered in hydraulic analysis.

Afflux (conceptual)

Upstream rise in water level caused by an obstruction or constricted flow; affects hydraulics and scour.

Freeboard

Vertical clearance above DFL/MFL; typically 1.5 m (debris-prone rivers) or 1.0 m (other bridges); must meet navigational clearance requirements (HWL + HV + 1 m) and be suitable for coastal wave considerations.

Navigation Clearance

Vertical and horizontal clearances required for navigable waterways; permit from Philippine Coast Guard.

Air Clearance

Clearance requirements for bridges near airports; permit from CAAP.

Highway Vertical Clearance

Minimum vertical clearance for the roadway, typically at least 4.88 m, with additional allowance for future resurfacing (0.15 m) and full roadway width clearance.

Underpasses

Vertical clearance requirements for underpasses; pier placement typically 9.0 m from traffic lanes with protective barriers.

Tunnels

Minimum wall clearance and width requirements for two-lane tunnels (at least 9.0 m between walls).

Through-Truss Clearance

Minimum vertical clearance from roadway to overhead cross-bracing (not less than 5.3 m).

Depressed Portions

Minimum width between walls for depressed roadways carrying two lanes (typically 9.0 m); curb width not less than 450 mm.

Bridge Deck Drainage

Drainage design to remove runoff from the deck to abutments and existing stormwater systems; designed for a 5-minute duration, 10-year rainfall (Volume 3 guidance).

Curbs and Sidewalks

AASHTO LRFD guidance on curb shapes, widths, sidewalk separation, and accessibility features (PWD).

Railings

Primary function is vehicle containment and safety; materials and standards (concrete preferred; steel allowed; wooden/timber not allowed; continuous handrails for safety).

NAMRIA

National Mapping and Resource Information Authority (source of base maps for catchment delineation).

WSPRO / HEC-RAS

One-dimensional hydraulic analysis software used for bridge hydraulics (standard-step method in WSPRO; HEC-RAS).

Annex A (Volume 3)

Annex with scour methods and detailed calculations referenced in 3.3.8.

AASHTO LRFD 2012

American Association of State Highway and Transportation Officials Load and Resistance Factor Design 2012 standards used in hydraulic design.