Airports and Harbours

Aircraft characteristics affecting airport design

Airport site selection

Factors considered:

1. Regional plan and airport type (domestic/international, civil/military).
2. Proximity to other airports — non-interference of air traffic patterns.
3. Ground accessibility — travel time from the city; road and rail links.
4. Topography — level land, minimum earthwork; freedom from flooding.
5. Obstructions — hills, towers and tall buildings must not penetrate approach and other imaginary surfaces.
6. Visibility — freedom from fog, smoke and haze (industrial areas).
7. Wind direction and intensity — for runway orientation.
8. Noise nuisance — away from dense residential areas; compatible land use.
9. Soil and drainage — good bearing capacity, low water table.
10. Future expansion — adequate land.
11. Utilities — water, power, telecommunications.
12. Economy — land cost, construction cost.
13. Bird hazard — away from garbage dumps, slaughterhouses and water bodies attracting birds.

ICAO aerodrome reference code

The code relates aircraft characteristics to aerodrome facilities.

E.g. 4E for large wide-body jets; 4C for narrow-body jets such as common single-aisle airliners.

Components of an airport

Airside: runways, taxiways, holding bays, aprons, hangars, fuel facilities, air traffic control tower, navigational and visual aids, fire and rescue services. Landside: terminal building, car parks, access roads, cargo terminals, utilities, administrative buildings.

Runway orientation

Runways are oriented along the direction of prevailing winds so that aircraft take off and land into the wind (increasing lift, reducing ground run) and crosswind components are within safe limits.

Wind rose diagram

• Type I — shows direction and duration (percentage of time) of winds; radial lines proportional to wind duration in each direction; runway placed along the longest line.
• Type II — shows direction, duration and intensity; concentric circles for wind speed ranges; a transparent strip of width equal to twice the permissible crosswind component is rotated over the diagram to find the orientation giving maximum wind coverage (usability).

Crosswind component $=V\sin \theta$ ($V$ = wind speed, $\theta$ = angle between wind direction and runway).

ICAO recommendations: runway usability factor at least 95%, with maximum permissible crosswind components of about 37 km/h (20 knots) for aircraft needing a reference field length of 1500 m or more, 24 km/h (13 knots) for 1200–1500 m, and 19 km/h (10 knots) for less than 1200 m.

Runway designation: runway ends are numbered by their magnetic bearing divided by 10, rounded (e.g. a runway oriented 272° magnetic is "27", its reciprocal end "09"); parallel runways add L, C, R.

Runway configurations

Single runway, parallel runways (close, intermediate or wide spacing), intersecting runways, open-V runways, and combinations — selected based on traffic volume, wind coverage and land availability.

Runway length

Basic runway length

The length required under standard conditions: airport at mean sea level, standard atmosphere (15 °C at sea level), zero effective gradient, no wind, aircraft at maximum take-off/landing weight. Considered cases:

1. Normal landing — aircraft must stop within a proportion of the runway.
2. Normal take-off — with a margin.
3. Engine failure — the runway must allow either continued take-off or aborted (rejected) take-off and stopping; this defines the balanced field length.

Clearway — an area beyond the runway end, free of obstacles, over which the aircraft makes its initial climb. Stopway — a paved area beyond the runway end that can support an aircraft during an aborted take-off.

Corrections to basic runway length (ICAO/FAA)

Runway geometric elements

• Runway width — depends on code letter/number (wider for larger aircraft).
• Longitudinal gradient — limited (ICAO: about 1.25% maximum for code number 4 runways, 1.5% for code 3, 2% for codes 1 and 2), with limits on changes of gradient and sight distance along the runway.
• Transverse slope — for drainage (typically about 1–1.5%).
• Runway shoulders, runway strip (graded area around the runway), runway end safety area (RESA), blast pads.

Taxiways

Taxiways connect runways with aprons, hangars and terminals. Design considerations: shortest practicable routes, avoid crossing active runways, adequate width and separation, smooth curves, sight distance.

Exit taxiways

• High-speed (rapid) exit taxiways allow landing aircraft to leave the runway at higher speeds, increasing runway capacity.
• Commonly angled at about 30° to the runway (ICAO range about 25°–45°).

Water transportation

Water transport is the cheapest mode for bulk and long-distance freight — most of India's international trade by volume moves through seaports. It includes ocean (maritime) transport, coastal shipping and inland waterways (rivers, canals).

Advantages: low cost per tonne-km, high capacity, energy efficient, natural routes. Limitations: slow, depends on ports and navigable depths, weather and seasonal restrictions, needs transhipment to other modes.

Definitions

Every port has a harbour, but not every harbour is a port.

Classification

Harbours

Ports

• Ocean (sea) ports, river ports, inland ports (dry ports/inland container depots).
• By function: cargo ports (bulk, general, container), passenger ports, transhipment ports, free ports.

Ports in India

India's ports are grouped as major ports (under the Union Government, administered through major port authorities) and non-major (minor) ports (under state maritime boards/governments). There are twelve operational major ports on the west and east coasts; Vadhavan in Maharashtra has been approved as a new major port. The Sagarmala programme promotes port-led development, and the Indian Ports Act and the Major Port Authorities Act, 2021 govern port administration.

Site selection for a harbour

1. Natural protection from winds, waves and currents; minimum breakwater length.
2. Adequate depth of water (minimum dredging) and sufficient area for manoeuvring and future expansion.
3. Good holding ground for anchorage and suitable foundation conditions for structures.
4. Minimum littoral drift and siltation.
5. Favourable tidal range, currents and climate.
6. Hinterland — productive area with trade potential; good rail, road and pipeline connections.
7. Availability of construction materials, fresh water, power, labour.
8. Defence considerations and environmental impacts (coastal ecology, CRZ).

Harbour planning

• Size — based on the number and size of ships, berths needed, anchorage and manoeuvring areas.
• Depth below the lowest low water (chart datum) = maximum draft of the design ship + squat (sinkage when moving) + trim + allowance for wave-induced motion + keel clearance (depends on bottom type) + siltation allowance.
• Entrance — wide enough for safe navigation but narrow enough to limit wave penetration; oriented to avoid beam seas; located away from zones of heavy littoral drift.
• Turning basin — area for ships to turn; diameter commonly about 1.5 to 2 times the length of the largest ship (smaller with tug assistance).
• Approach channels — width based on ship beam, one-way or two-way traffic, currents and cross-winds.

Natural phenomena

Winds

Winds generate waves and currents and influence harbour layout (entrance orientation, berth alignment). Wind speeds are described by the Beaufort scale; wind roses summarise directions and intensities.

Waves

• Wave height ($H$) — vertical distance between crest and trough; wavelength ($L$); period ($T$).
• Wave height increases with wind speed, duration and fetch (the open-water distance over which wind blows).
• Deep-water waves — water depth $d>L/2$; shallow-water waves — $d<L/20$; transitional in between.

• As waves approach the shore they shoal (height increases), refract (bend towards shallower water), diffract (spread behind obstacles such as breakwater ends), reflect (from vertical walls) and eventually break.

Tides

Tides are periodic rise and fall of the sea surface caused mainly by the gravitational attraction of the moon and sun.

• Spring tides — highest high tides and lowest low tides, at new moon and full moon (sun and moon aligned).
• Neap tides — smallest tidal range, at the first and last quarters of the moon.
• Most coasts have semi-diurnal tides (two highs and two lows a day); some have diurnal or mixed tides.
• Tidal range influences quay heights, dock gate design (lock/wet docks where the range is large, e.g. the Gulf of Khambhat) and navigation windows.

Currents and littoral drift

• Currents are caused by tides, winds, river discharge and density differences.
• Littoral drift — movement of sand along the shore by longshore currents generated when waves approach the coast obliquely. Breakwaters and jetties interrupt the drift: sand accretes on the updrift side and the coast erodes on the downdrift side; harbour entrances silt up.
• Control: proper location and orientation of entrances, groynes, sand bypassing (dredging sand from the updrift side to the downdrift side), maintenance dredging.

Breakwaters

Breakwaters are structures built to protect the harbour area from waves, creating calm water for berthing and cargo handling. They also reduce siltation and protect the shore.

Types