Navigation implies use of water courses for transportation of passengers and goods. According to the navigation area, they distinguish sea-going, inland, and combined navigation types; according to the function, there are mercantile, fishing, etc. navigation types.

Present-day navigation is based on comprehensive facilities (vessels and equipment) and services providing support to navigation (dock/terminal, hydrometeorological, hydrographic, emergency rescue, maintenance services, etc.).

Shipping restrictions are due to navigation-related problems, hydrometeorological conditions, and maritime law. Among the navigation-related problems that affect the frequency of navigations are: freezing up of northern seas and inland waterways in temperate climatic zones; low tides accompanied by changes in depth; limited depth of natural waterways. Navigation in freezing water bodies can be extended by using ice-breakers or by enhancing the ice-resistance of vessels. To increase the depth, channel dredging operations are carried out and river level is controlled by means of dams.

Hydrometeorological conditions restrict navigation if near-water ships are used (e.g. when an inland-waterways vessel go to cross the sea, etc.). Navigation regime is regulated by national laws and international treaties.

Agreements at the Global and Regional Levels

Convention on the High Seas (Geneva, 1958) 

Convention on The Territorial Sea and the Contiguous Zone (Geneva, 1958) 

Recreation is the complex of health promotion actions aimed at the restoration of normal well-being and work capacity of an healthy but tired person.

This concept covers all types of recreation, i.e. treatment at a health resort and tourism.

Restoration of emotional and psychological strength, health, and work capacity by taking a rest outside the home: in the open air; in tourist trip; etc.

Sanatoria, preventive clinics, boarding houses, etc. are considered as specialized facilities for recreation. This concept has been used since the 1960 in the physiological, medical, social & economic literature in relation to the recovery of strength and health of workers;

Hydraulic transportation is the means to transport solid materials by water stream. Hydraulic transport is used for hydraulic mechanization of earth excavation and mining works, construction of earth structures (dams, dieks, etc.), removal of slag and ash from large boiler rooms, transportation of minerals and removal of their washery refuse (refuse wood and paper pulp, sugar mill and distilling plants, etc.).

Hydraulic transport is divided into gravity-flow transmission and forced-flow transmission. With gravity-flow transmission, hydromixture moving through gravity chutes (shoots) and partially filled pipes has free surface the pressure on which is equal to atmospheric one; with forced-flow transmission, hydromixture in pipelines is under excess pressure. This pressure is generated by pumps (e.g. slush pump, coal pump, etc.). Sometimes, pressure generated due to the difference between the pipeline entry and end levels (for example, when transporting rock to a mine for laying a mined-out space).

Hydraulic transportation is carried out only at a hydromixture velocity not lower than a certain minimum value, so called a critical value. Depending on the density and size of transported particles, hydromixture concentration, and pipeline diameter, the critical velocity varies from 1.5-2 to 4-5 m/s. At such velocities, small and light particles are transported being suspended; medium-size and medium-weight particles, in intermittent suspension; and the biggest and heaviest ones, by dragging and floating along the pipeline bottom. Only for highly-concentrated hydraulic mixtures composed of finest particles of clay, chalk, turf, coal, etc., such hydromixtures have peculiar properties like colloids: particles in them are retained in suspension even at rest. Forced-flow transmission allows conveying materials for long distances.

Estimation of hydraulic transportation as a rule boils down to the determination of the pipeline diameter (according to specified productivity and critical velocity value), solids concentration in the hydromixture, and hydraulic resistance. The hydraulic resistance and hydroabrasive wear of the pipeline is going down dramatically with reducing size of the particles being transported down to less than 1-3 mm; therefore, the scope of the application of hydraulic transportation for long distance is generally limited to the particles with such a size.

The advantage of hydraulic transportation consists in high capacity, possibility to transport for long distance, full automation, low operating costs, and possibility to combine transportation with other process technologies (hydraulic fragmentation, enrichment, and washing of the material).

The disadvantage of hydraulic transportation is considerable water and electric power consumption, tear and wear of pipelines and pumps when transporting abrasive materials, and in some cases grinding and saturation of the materials being transported and need for their following dehydration.

Source: Yandex Dictionary