| Term No. | Term Name | Term Description |
| 7867 | Natural hazards | Natural processes or phenomena occurring in the biosphere that may constitute a damaging event. Natural hazards can be classified by origin namely: ge..... |
| 1523 | Natural levees | High banks formed along the channel edges during high floods due to silting along the banks...... |
| 7102 | Natural pollutant | A substance, not of man-made origin, that produces adverse environmental effects when present in excess..... |
| 5557 | Natural pozzolans | Pozzolans occurring in nature are used as such in natural state or after grinding them to required fineness. These include volcanic ash and its deriva..... |
| 1135 | Natural recharge | Water that gravitates to the zone of saturation under natural conditions...... |
| 5773 | Natural resins | Include all the naturally occurring resins that are used in varnish manufacture...... |
| 6783 | Natural resources | Those natural elements of the environment that are regarded as useful for consumption and/or enjoyment by mankind...... |
| 8643 | Natural Resources Vector | Vector of natural resources; when activities use natural resources, upper maximum of natural resources becomes constraints to the activities. This vec..... |
| 6742 | Natural selection | The process of survival of the fittest, by which organisms that adapt to their environment survive and those that do not disappear. ..... |
| 3308 | Natural surface level, or Ground levels | Levels above datum of the natural surface line...... |
| 3307 | Natural surface line | Line joining points of the natural ground surface parallel to or along the centre line of the bed of a canal...... |
| 1089 | Natural water table | The surface at which the hydrostatic pressure of the groundwater is equal to the atmospheric pressure...... |
| 4145 | Natural well | An abrupt depression in the land surface, not made by human agency, which extends into the zone of saturation but from which water does not flow to t..... |
| 4180 | Naturally-filtered well, Naturally-screened well, or Naturally gravel- packed well | A well that taps an aquifer imperfect sort or at least partly incoherent material, and whose specific capacity has been increased by the removal of th..... |
| 6805 | Nature reserve | An area of land and/or water, managed primarily to safeguard the fauna, flora and physical features that it contains...... |
| 3170 | Navier-Stokes equation | Momentum equation applied to a small control volume of incompressible fluid; usually written in vector notation. ..... |
| 9167 | Navigation benefits | Direct benefits based on saving to shippers compared to alternative cost, saving in time and operating cost from improvement of an existing waterway, ..... |
| 4630 | Navigation canals | Canals constructed primarily for shipping...... |
| 8804 | Navigation project | Project meant solely or primarily for navigation purposes, although in the latter case it may incidentally serve other purposes...... |
| 3320 | Navigation structures | Structures built in canals and canalized or navigable waterways where headway and other facilities exist or are provided for the direct passage of ves..... |
| 1638 | Nazzaz | A compact, impermeable pan, concretionary in character, occurring at a slight depth below the surface of red sandy soils in the Levant...... |
| 2017 | Neap tide | A tide occurring near the time of the quadrature of the moon with the sun. The neap tidal range is usually 10 to 30 per cent less than the mean tidal ..... |
| 1311 | Neap tides | Exceptionally low tides that occur twice each month when the earth, sun and moon are at right angles to each other...... |
| 6304 | Near infrared | The shorter wavelengths in the infrared region, extending from about 0.7 micrometres (visible red) to around 2 or 3 micrometres...... |
| 6750 | Nearctic | Zoogeographical region that includes North America to approximately the middle of Mexico and Greenland...... |
