Drainage and Hydrology

Drainage

Means of collecting, transporting, and disposing of surface water originating in or near the right of way, or flowing in stream crossings or bordering the right of way

Hydrology

branch of physical geography that deals with water of the Earth.

Rational Methods

Empirical Formula

Unit Hydrograph

Statistical Approach

Simulation

5 Methods in Predicting Runoff

Any existing drainage system patterns and soil cover should NOT be disturbed.

Necessary changes in the drainage patterns should NOT in any manner bring velocities that may create new erosion problems.

2 Cardinal Rules on Drainage Design

Economy

In drainage design, it means finding the solution to a problem that is cheapest in the long run

Determine the initial investment cost

Consider the maintenance cost or outlay

Consider anticipated loss or damage

3 Drainage Economic Conditions

Sub-critical flow

Happens when the slope is mild.

Water moves relatively slowly, and the depth of flow is greater than the critical depth.

Super-critical flow

Happens when the slope is steep.

Water moves fast, and the depth is less than the critical depth.

Critical depth

Occurs when the velocity head is one-half the average depth.

Average/Mean depth

The cross-sectional area of the flow divided by its width at the liquid surface.

Divert water to other areas.

Widen or lengthen the channel (makes the flow slower).

Decrease the slope of the channel

Install baffles, checks, or drops to break the flow energy.

4 Methods to Reduce Velocity

Corrugated metal pipes

They can deform laterally and "push back" against surrounding soil. This deformation helps share the load, increasing load capacity compared to rigid pipes.

Follow natural alignment.

Avoid sharp deviations.

Skewed culverts (angled to the road) are acceptable.

Avoid inverted siphons.

Prevent stagnant water.

Headwalls and end walls provide structural integrity and scour protection.

Hydraulic and structural function of walls must be considered.

Cut-off walls (or aprons) are necessary for scour protection.

Discouraged practice: Small pipe ends and walls.

Better practice: Extend the culvert beyond the embankment toe.

Legs headwall.

Wing Type Walls.

U-head walls.

Warped walls.

14 Key Guidelines in the installation of Culverts 

Vertical elongation

Temporary intentional diametral deformation to increase the vertical diameter of a flexible pipe

Standard Pipe Measurement

Pipe conduit of different types and sizes will be measured according to the linear meter installed.

Sloped/Skewed Ends

Conduit with sloped or skewed ends will be measured along the invert (the lowest point of the pipe's internal cross-section).

Units

Every section will be measured according to the number of units installed

Class B Bedding (Footing) Material

These materials will be measured in place by cubic meter

Concentration of Flow

Poor Design or Maintenance

Liability

Engineering Decisions

Damage claim against the department could be establish if: (4 CPLE)

Capillarity

Tendency of water to flow through the pores and fine channels of soil, acting as a force that pulls water through soil voids in all directions

Slide

Occurrence where the moving earth mass is defined and separated from the underlying and adjacent earth by a plane (or multiple adjacent planes)

Rotational Slide

Translational Slide

Block or Wedge Failure

Flows and Spread Failure

4 Classifications of Slide (RTBF)

Block or wedge failure

Displacement of an intact mass of soil due to the

action of an adjacent zone of earth

Flow

It involves lateral movement of soil having a characteristic of viscous fluid, although the actual consistency of the moving mass may vary from very wet to dry.

Spread

Refers to the occurrence of multi-directional lateral movement by a fractured soil mass

Rotational slide

A type of slide where the movement occurs along a curved, concave-upward slip surface, causing the mass to rotate about an axis roughly parallel to the slope contours

Translation slide

A slide in which the mass moves downslope along a relatively planar or undulating surface with little rotation, often along structural features like bedding planes.

Benkelman beam

A simple lever-arm device used to measure the deflection of flexible pavements under the action of moving wheel loads

Reduce/Correct Loading

Increase Shear Strength (Structural)

Analyze Soil Characteristics

Flatten Slope (Where Space Allows)

Add Toe Beam

Protect Toe from Erosion

Manage Water

Use Grouting/Injection

8 Methods in Improving the Stability of Slope

Masonry walls

These walls rely on the mass and careful placement of stone. They are categorized by the use of mortar, which dictates their drainage and rigidity

Dry rubble retaining wall

Uses unmortared stones (rubble), relying on the gravity and mechanical interlock of the stones for stability

Cement rubble retaining wall

Uses stones set in cement mortar to fill all voids, resulting in a monolithic, rigid structure with increased strength and erosion resistance

Reinforced concrete walls

These walls are used for greater heights and require a precise structural design, with stability achieved either through mass or through a cantilever action

Reinforced concrete gravity wall

Similar to masonry gravity walls, it relies primarily on its self weight (mass) and the resulting friction at its base to resist lateral earth pressure.

Reinforced concrete cantilever wall

The most common type for heights up to about 25 feet.

It's more efficient than a pure gravity wall because it leverages structural rigidity.

Retaining walls

Structures designed to restrain soil or rock from a slope or change in elevation that it would not naturally keep to, often used in mountainous areas or where space is limited

Stem

The vertical section of the wall that rises from the base

Footing

The wide, horizontal base that extends beneath the stem.

Heel

The part of the footing extending back beneath the retained soil

Toe

The part of the footing extending forward in front of the stem.

Shear key

Vertical projection cast monolithically underneath the footing

Drainage

Collective elements used to remove water from behind the wall

French drain

A perforated pipe installed at the base of the wall, typically within the granular backfill. It collects water that seeps through the backfill and directs it to an outlet. The pipe should be wrapped in geotextile fabric to prevent clogging.

Weep holes

Small openings or conduits (typically 6 to 10 feet apart) installed through the wall stem at the base. They provide an exit for collected water, especially in the absence of or in addition to a full drain pipe system.

Hand Laid Rock Embankment

A constructed embankment primarily of rock where the stones are carefully placed, often by hand, to arrange interlocking and stability, typically for road foundations or site slopes.

Stability against overturning

Stability against sliding

Stability against bearing capacity failure

Structural integrity

Adequate drainage

5 Requirements of a Good Retaining Wall Design

Riprap

A layer of large, angular stones, broken concrete, or other material placed on an embankment or shoreline to protect against scour erosion and water-induced displacement.

Grouted riprap

Riprap where the voids between the stones are filled with cement grout or mortar creating a rigid structure

Sheet piles

Structural sections with interlocking edges that are driven or vibrated into the ground to form a continuous barrier or retaining wall.

Gabion

Cage, cylinder, or box filled with rocks, concrete, or sometimes sand and soil for use in civil engineering, road building, and military applications

Straight web sections

Designed primarily to resist tensile forces (pulling forces) within the wall, as they are typically used to form cylindrical or diaphragm cofferdam structures

Z sections

The interlocks are located on the neutral axis of the wall, making them highly effective at resisting the bending moments caused by lateral earth pressure

Archweb sections

They provide good resistance to bending but are generally considered less structurally efficient than Z-sections for resisting bending moments

Highway bridges

Structures carrying a roadway over an obstacle (like a river, valley, or other road) and must be designed to safely carry various loads while managing environmental interaction

Dead load

The weight of the permanent structure, including the superstructure (deck, girders, railings), substructure (piers, abutments), and non-structural elements (pavement, utilities).

Live load

The weight and force of the vehicular traffic using the bridge. Standardized design vehicles (e.g., AASHTO design trucks) are used to represent the maximum expected load. This includes the weight of the vehicle and the impact force as the vehicle travels over the deck.

Centrifugal force

A horizontal force acting radially outward on the bridge when a vehicle travels on a curved alignment. The magnitude depends on the vehicle's mass, speed, and the radius of curvature.

Wind load

The force exerted by wind on the exposed area of the bridge structure and the live load. This is a significant lateral and uplift force, especially for long-span or high-elevation bridges