Water Resources PDF

WATER RESOURCES Earth is the only planet where water in its liquid form exists. In other planets, water occurs in the form of ice or vapor. As seen from space, Earth looks mostly blue and white because of water, snow, ice, and clouds on its surface. The part of Earth's subsystem containing...

WATER RESOURCES Earth is the only planet where water in its liquid form exists. In other planets, water occurs in the form of ice or vapor. As seen from space, Earth looks mostly blue and white because of water, snow, ice, and clouds on its surface. The part of Earth's subsystem containing the oceans, lakes, streams, underground water, and snow and ice, is the hydrosphere. It makes up about 71% of Earth's surface. However, water is also present in the other subsystems. It occurs as water vapor in the atmosphere, as an important constituent of minerals in the geosphere, and a fundamental component of living organisms in the biosphere. The existence of water in the different subsystems is part of the hydrologic cycle. The Hydrologic Cycle The Hydrologic Cycle , also known as water cycle, is the movement of water around Earth's surface and its subsystems. The cycle consists of interconnected pathways and reservoirs. Reservoirs are the places where water resides for varying amount of time, while pathways are the processes that allow water to move between each reservoir and subsystems. There is a mass balance in the cycle, maintaining the total amount of water. Fluctuations may occur on a local scale, such as the occurrence of flood and drought, but these are balanced out on a global scale. Heat coming from the sun provides energy for the movement of water. It causes evaporation or the process in which liquid water changes into vapor. It occurs in the ocean, surface water bodies, vegetation, and soil. About 80% of water vapor in the atmosphere evaporates from the ocean. Transpiration is the evaporation of water from the leaves and stems of plants, which contributes about 10% of the water vapor in the atmosphere. In high altitudes, ice can directly transform into water vapor in a process called sublimation. The water vapor enters the atmosphere and moves with the flowing air. As the air rises, it cools and slows down the movement of water molecules. This allows condensation, the change from vapor into liquid or solid, to occur. Water droplets group together and form clouds. When water droplets or ice crystals in the clouds become large and heavy, precipitation occurs. Precipitation transfers water from the atmosphere to Earth's surface in liquid or solid form as rain, snow, or hail. Rain that falls into the land surface penetrates the soil in a process called infiltration. When the soil becomes saturated, rainwater may flow over land as surface runoff and will join other bodies of water such as in streams, lakes, and oceans. Part of the water that infiltrates the ground will be stored as groundwater while some will be absorbed by plants or directly evaporate. Snow usually remains on the ground for one or more seasons and eventually melts and contributes to the water in streams. Water is locked up as ice in glaciers for a long time. Given the right conditions, the glaciers will eventually melt, evaporate, and return to the oceans. Earth's Waters Earth's Waters The total amount of water in the planet, also known as Earth's water budget, generally remains constant through time. Water moves and changes in form, but is neither created nor destroyed. Only a very small percentage is added to the hydrologic system by volcanic eruptions and meteors from space. Most of the water on Earth today have been cycling through the hydrologic system for billions of years. The United Nations World Water Development 2005 Report characterized the amount of water in the different reservoirs. The largest reservoir is the ocean that contains about 97.5% of Earth's total water, which is mostly saline water. This has a major implication in humans since humans depend on freshwater for drinking, agriculture, and industrial use. Freshwater, which is only 2.5% of Earth's total water, is found in glaciers (68.7%), groundwater (30.1%), permafrost (0.8%), surface water, and atmospheric water. The surface water in rivers, lakes, swamps, soil moisture, living things, atmospheric water vapor, ground ice, and permafrost, constitute only about 0.4% of the total freshwater supply or less than 0.02% of the total water on Earth. The residence time is the average length of time spent by water molecule in a reservoir. In large reservoir, the residence time of water is longer. Although the total amount of water in the planet remains constant, the volume of water present in each reservoir varies and their volumes affect other reservoirs. For instance, the melting of glaciers and ice caps in the Polar Region reduces the amount of water in these reservoirs. It also leads to the increase in the volume of water in the ocean. This is manifested as sea level rise, which could cause coastal flooding in low- lying coastal areas. Saltwater Reservoir An ocean is a vast body of saline water. There is only one global or world ocean and it covers 71% of Earth. It is geographically divided into five distinct regions and into numerous seas, gulfs, bays, and straits. Historically, the four recognized oceans are the Atlantic Ocean, Pacific Ocean, Indian Ocean, and Arctic Ocean. In 2000, the International Hydrographic Organization proposed the Southern Ocean. It is the body of water surrounding Antarctica and is connected to the Pacific, Atlantic, and Indian oceans. The total volume of water in the world's oceans is about 1340 million km³. The saltiness of saltwater is called salinity. The major chemical elements present in seawater are sodium and chlorine ions. Other natural elements are also present in seawater in very low concentrations. The salinity of seawater varies from 33 to 37 parts per thousand. When it is evaporated, three quarters of the dissolved material is comprised of NaCl (common salt). The principal sources of the elements dissolved in seawater are weathering and volcanic eruptions. Weathering, or the in-situ disintegration of geologic materials, releases soluble materials such as sodium, potassium, and sulfur. These materials are carried by streams into the sea. Volcanic eruptions, both on land and submarine, contribute compounds through volcanic gases and hot springs. The salinity of seawater is maintained within a narrow range by the processes in the hydrologic cycle. Evaporation removes water, making the remaining solution saltier. Precipitation adds water, causing dilution. Inflow from river and groundwater also makes the sea less salty. As sea water freezes, salt is excluded because of its structure, making the unfrozen seawater saltier.  There are three major zones in the ocean. The surface layer, which consists of relatively warm, low- density water, extends from the ocean surface to a depth of 100 m. This layer is only about 2% of the water in the ocean but it is the home of most marine plants and animals. The second layer is called thermocline, where the temperature of water decreases rapidly with depth. At high latitudes, the thermocline reaches the surface and extends up to 1500 m. Below the thermocline is the deep zone where the temperature is uniformly low. Eighty percent of the water in the ocean is in the deep zone. The waters in the different layers of the ocean are constantly moving. The surface of the ocean is affected by currents caused by prevailing winds. The air blowing on the surface drags the water forward, creating slow, broad drifts confined at a depth of 50 to 100 m. The surface ocean currents flow clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. In the deep zone, there is a thermohaline circulation driven by density differences, which is controlled by temperature (thermo) and salinity (haline). This circulation is propelled by the sinking of cold, salty, and dense water in the Polar Regions, and rising of the warm, less salty water of the Tropics. The ocean is one of the most valuable resources on the planet. Aside from providing the voluminos marine food sources, it is also used in transportation and recreation. More importantly, it plays a vital role in regulating the climate through its interaction with the atmosphere. It absorbs and circulates heat, water, and carbon dioxide, which are vital in the many chemical cycles on Earth. Freshwater Reservoirs Most of the freshwater on Earth is stored in glaciers situated in inaccessible areas such as the Polar Regions and high mountains. The readily available freshwater sources are the surface water reservoir and groundwater reservoir. Glaciers and Ice Sheets A glacier is a permanent body of ice, which consists largely of recrystallized snow. In Polar Regions and high-altitude regions, not all of the snow that fall melts because of very cold temperature even during summer. The unmelted snow is covered by another layer the following winter. The snow gradually accumulates and becomes compacted, turning into a mass of ice. An ice sheet is a mass of glacial land ice extending more than 50000 km². There are currently ice sheets covering most of Greenland and Antarctica. During the last ice age, ice sheets also extended to North America and Scandinavia. The freshwater stored in glaciers and ice sheets are estimated to exceed 24 million km. Almost 90% is concentrated in Antarctica while the rest is found in Greenland and in mountain glaciers. If the ice sheet in Greenland were to melt, it would cause the global sea level to rise by 6 meters. If the Antarctic ice sheet melted, the sea level would be about 60 meters. Glaciers and ice sheets influence global climate and the hydrologic cycle. During glaciation, large amount of water becomes locked up as snow, resulting to a decrease in the volume of runoff, lower sea level, and exposure of more land in the coastal areas. When deglaciation occurs, the reverse happens-river flow increases, and the volume of the world ocean increases, resulting to a rise in sea level and reduced land area. Permafrost A soil, rock, or sediment that is frozen for more than two consecutive years is called permafrost. The frozen ground varies in thickness from a few meters to about 150 meters. The upper 30 cm to 100 cm of soil thaws during summer and refreezes during winter. Most of the permafrost is found in Polar Regions, although they may exist in high-altitude regions. The total water stored as underground ice in a permafrost is estimated to be 300000 km. It comprises about 0.8% of the total freshwater resource. Surface Water Reservoirs Surface waters include the streams, lakes, and wetlands where water from rainfall, melting snow and ice, and groundwater flows. They represent 0.3% of Earth's total water resource. This resource is harnessed for irrigation, recreation, transport, fishing, drinking, and hydropower. Stream A stream is a moving body of surface water that flows downslope toward sea level because of gravity. It has clearly-defined passageway called channels where particles and dissolved substances are transported. A river is a stream with a considerable volume and a well-defined channel. Streams are interconnected and form a tree-shaped network of small streams, making up the branches and joined to a large main stream or river, which comprise the trunk. The smaller streams are also called tributaries. The land area in which the water flow into a particular stream is called a drainage basin ot watershed. The line that separates individual drainage basin is called drainage divide. It is a topographically high landform usually represented by mountain ridges or hills in smaller basins. The narrow, elongated landform separating individual streams within a basin is called interfluve. During heavy rain, water moves downhill in a process called overland flow. After a short distance, the water enters the channels and becomes streamflow. Overland flow and streamflow contribute to surface runoff. These processes initiate the transport of sediments along their courses, carving complex patterns in the landscape. Rivers constitute about 1.6% of the total surface and atmospheric water. The total volume of water stored in streams is estimated at about 2120 km². Drainage basin varies in size from less than a square kilometer to subcontinental size, like the Amazon River Basin and the Nile River Basin. The drainage area of the world's twenty largest river basins range berween 1 and 6 million km². In the Philippines, the largest drainage basin is the Cagayan River Basin, which comprises a total area of 27 280 km². This drainage basin is bounded by the Cordillera, Caraballo, and Sierra Madre Mountain ranges. The total length of Cagayan River, from Nueva Vizcaya to Aparri is 505 km. Lakes Lakes are large inland bodies of fresh or saline water. Its upper surface is exposed to the atmosphere and is essentially flat. It forms in places where water collects in a low area (depression) and behind natural or humanmade dams. Ponds are small and shallow lakes. Dams are barriers constructed along streams to contain the flow of water. Water in the lakes came from streams, overland flow, and groundwater Water exits from lakes through outlet streams or by evaporation and infiltration into the ground.  Geological processes form natural lakes. For example, a landslide or lava flow could block a stream and create a natural barrier. Water will accumulate behind the barrier and will form a lake. Collapse of volcanic craters also creates depression that is eventually filled with water, like the crater lake of Mt. Pinatubo and Taal Volcano. Lakes store 67% of the total surface and atmospheric water. This is a tiny percentage of Earth's total water but it is an extremely important water resource. It provides freshwater for irrigation, industrial, municipal, residential, and recreational purposes. Depending on their size, lakes could also be used as transportation routes. Wetlands Land areas where water covers the surface for significant periods is referred to as wetlands. They vary in size-from relatively large in flat areas to small in steep areas. Wetlands are biologically diverse environment filled with species that rely on both the land and water for survival. It is also a fragile ecosystem that is sensitive to the amount and quality of water. Wetlands constitute about 8.5% of the total land surface and atmospheric water. The largest wetland in the Philippines is Ligawasan Marsh found in the provinces of Maguindanao, North Cotabato, and Sultan Kudarat. It covers an area of 2200 km². The types of wetlands include marshes, swamps, and estuaries. 1. Marsh is a shallow wetland around lakes, streams, and oceans where grasses and reeds are 1 the dominant vegetation. The wetland in Candaba, Pampanga is an example of a marsh ecosystem. 2. Swamp is a wetland with lush trees and vegetation found in low-lying areas beside slow- moving rivers, oxygen in the water is typically low and swamp plants and animals are adapted to these low-oxygen conditions. Mangrove forests are unique example of swamp ecosystem that tolerates salty conditions. 3. Estuary is a partly enclosed coastal body of water where freshwater from stream meets the salrwater from the sea. It is home to many organisms that can tolerate the sharp changes in salinity due to the constant change of salt content. The mouth of large rivers such as Pampanga River in Manila Bay is an estuary. Wetlands harbor great biological diversity. It is an important breeding ground for fish and invertebrates. Its ability to trap water serves as a sponge that slows down stream flow and minimizes floods, erosion, and sedimentation. Water trapped in the wetlands are also able to seep into the ground and replenish the groundwater. As a sponge, it also traps pollutants that could otherwise flow to other bodies of water. Floods A flood is a natural event wherein an area that is usually dry is submerged under water. It usually occurs when the rate of precipitation is higher than the rate in which it could be absorbed by the ground or carried by streams. It can also occur even during dry periods when natural or humanmade reservoirs collapse. Some floods occur suddenly and recede quickly, while others lasts for few days to several weeks. It occurs at irregular intervals and varies in size, duration, and extent of affected area. Fluvial or riverine flood occurs when a stream's discharge is greater than the capacity of the channel, causing the stream to overflow. Flashfloods are characterized by intense, high-velocity torrent of water that occurs in an existing river channel with little to no notice. Coastal flooding occurs when water overwhelms in low-lying areas along the coasts, usually due to severe weather conditions. Pluvial or surface water flood occurs when heavy rainfall creates a flood event independent of an overflowing stream. This is common in urban areas when the drainage systems are clogged. Vegetation plays an important role in reducing flood intensity. Plants can slow down the overland flow, giving it enough time for water to infiltrate the ground. When in saturated grounds, it still lengthens the time of arrival of water. It also decreases the number of sediments that could be eroded by surface runoff. Groundwater Groundwater is fresh water found in the rock and soil layers beneath the surface. The groundwater is the largest reservoir of liquid fresh water on Earth. It constitutes about 30.1% of the total freshwater on the planet. Water-bearing rock layers are called aquifers, akin to a "sponge" that holds groundwater in tiny cracks, cavities, and pores between mineral grains. Porosity is the total amount of empty pore spaces in the rock. It determines the amount of groundwater that an aquifer can hold. Loose materials such as sand and gravel have high porosity and can hold large amount of water. Crystalline rocks such as basalt and diorite have low porosity. The movement of groundwater within the aquifer is also controlled by the permeability of the material. Permeability is the ability of the rock or sediments to allow water to pass through it. In permeable materials, the pore spaces are interconnected throughout the rock, allowing the free flow of groundwater. Porous materials do not necessarily have high permeability. Clay and mud are porous materials but have low permeability. Sandstone, conglomerate, limestone, loose sand, and highly- fractured rocks are examples of materials with moderate to high permeability and make good aquifers. Groundwater Profile When a well is excavated in the ground, the first layer encountered is the moist soil layer on the surface. Beneath this is a zone in which the spaces between the particles are filled mainly with air. This is called the zone of aeration or unsaturated zone. The layer beneath the zone of aeration is the zone of saturation. In this layer, the spaces between the particles are filled with water. The boundary between the zone of aeration and the zone of saturation is the water table. Directly above the water table is a layer called capillary fringe, wherein groundwater seeps up to fill the pore spaces in the zone of aeration by capillary action. The shape of the water table resembles the topography it is high beneath hills and low beneath valleys. Its location also fluctuates depending on the season. During wet season, the water table is found at shallow depths. It migrates deeper below the ground during the dry season, resulting to drying of shallow wells. Aquifers, Artesian Wells, and Springs A reliable groundwater supply can be obtained from aquifers with good porosity and permeability such as coarse-grained clastic sedimentary rocks. An aquifer in which the groundwater is free to rise to its natural level is called unconfined aquifer. Water is open to the atmosphere through pores in the soil and rock above the aquifer. In a confined aquifer, the water is trapped and held down by pressure between impermeable rocks called aquiclude. The pressure in confined aquifer will cause water to rise in wells drilled through it. Water could rise in this well without pumping if the well is located at an elevation, which is below the recharge zone of the confined aquifer. This is called artesian well. A perched water table or aquifer occurs when there is a localized aquiclude above the main water table. It stores a relatively small amount of groundwater. The land area where water enters the ground and replenish the groundwater is called the recharge zone. For unconfined aquifers, this is basically the whole drainage basin or watershed. In confined aquifers, the recharge zone is limited only in areas where the aquifer is exposed to the surface. The discharge zone is the area where the groundwater flows out of the aquifer and onto land surface or even in submarine environment. A well in which groundwater is pumped our is also a discharge zone. When groundwater emerges to the ground surface, it creates a spring. Spring occurs usually in places where there is a decrease in permeability of the underlying material, such as presence of an aquiclude below an aquifer. Groundwater-Stream Relationship There is an interaction between groundwater flow and stream flow. There are streams that lose water downstream and dry up. In this type of stream, the water flows underground and contributes to the groundwater. This type of stream is called losing or influent stream. In contrast, there are also streams that are fed by groundwater. This stream is referred to as gaining or effluent stream. A stream or segments of large streams could either be gaining or losing depending on the amount of available water. For example, during dry seasons, the lower part of the stream could dry up, turning it into a losing stream but when there is abundant water in the wet season, it will flow again as a gaining stream. Water as a Resource Most of the early human civilizations were developed along the world's greatest rivers-the Tigris and Euphrates of Mesopotamia, the Nile River of the Egyptians, and the Yellow River of the Huang-He civilization. Their vast floodplains supported agriculture and the large channels allowed commerce to flourish. Today, billions of people are still dependent on water channels for food, water, transportation, recreation, and religious activities.  Activities Affecting the Quality of Water Throughout the world, there is an increasing pressure in Earth's water resources. This is mainly due to how human activities have sped up and caused climate change and variations in natural conditions. The human activities affecting water resources include the following: 1. Population growth, particularly in water-short regions 2. Movement of large number of people from the countryside to towns and cities 3. Demands for greater food security and higher living standards 4. Increased competition between different uses of water resources 5. Pollution from factories, cities, and farmlands. The degradation of ecosystems is one of the serious threats, which occur due to changes in landscapes deforestation, conversion of natural landscapes into farm or residential areas, urban growth, road-building, and surface mining. These activities have led to too much soil and sediments delivered to streams in a process of sedimentation. Mining of certain metals have also caused surface water to become acidic, producing a discharge called acid mine drainage. Improper waste disposal contributes significantly to the degradation of streams and lakes in urban areas. These results to damages in the aquatic ecosystems, impairs water quality, and hinders water transport in large bodies of inland waters. In the Philippines, the wetlands along Pampanga River and in the coastal areas of Manila Bay in Bulacan are converted into fishponds for aquaculture. This permanently alters the wetland ecosystem, aggravates flooding, and promotes excessive groundwater withdrawal. Wastes produced by human activities pollute the air, land, and water. They affect rainwater and water resources both surface and underground. The sources of freshwater pollution include industrial wastes, sewage, runoff from farmland, cities, and factory effluents, and the build-up of sediment. Emissions from factories and vehicles also pollute the atmospheric water and results to acid rain. Nutrients coming from sewage and from farmland runoff may lead to eutrophication in the receiving water reservoir and cause excessive aquatic plant growth that could have damaging ecological effects. Overexploitation of the surface and groundwater resources often causes irreversible effects. Lakes and streams have dried up in some regions due to excessive water withdrawal and improper management. For example, only 25% of the water in Aral Sea in Central Asia remains after the water from its feeder rivers was diverted for agricultural use. The consequences of excessive groundwater withdrawal include reduced spring yields, diminished river flow, poorer water quality, damage to natural habitats, and the gradual sinking of land known as subsidence. Studies conducted by the National Institute of Geological Sciences and Marine Science Institute in the University of the Philippines have shown that the ground subsidence in Rosario, Cavite, and CAMANAVA area in Metro Manila are related to extraction of groundwater. Natural phenomenon such as climate change also contributes significantly to the existing stress in the water resources. Extreme conditions such as drought have forced people to pump out more groundwater or diver stream flows. During extreme wet seasons, floods are very common and more severe, causing an increase in sedimentation from already denuded landscapes. Global warming also plays a vital role in the shrinking of glaciers and the consequent rise of sea level. Water Resource Management and Conservation The ever-increasing pressure in the water resources calls for an effective water resources management. It involves planning, developing, distributing, and managing the optimum use of water resources. Successful management requires accurate knowledge of the available resources and demands and mechanisms necessary to translate policies into actions. In response to growing water demands, various countries and regions have become determined in addressing the natural viability of water resources. These include rainwater harvesting for direct consumption and for replenishment of groundwater. Surface water is also diverted into basins in recharge zones to increase infiltration, reduce evaporation, and improve water quality. Dams and reservoirs are built to provide additional water storage. Interbasin transfer of water also augments the water supply in heavily stressed systems. For example, the Ipo transbasin tunnel transfers water from Angat River to La Mesa Dam, augmenting the water supply required for Metro Manila. Current technological advances make the wastewater reusable after extensive treatment to remove biodegradable materials, nutrients, and pathogens. Nonpotable water can be used for irrigation, in industry, to maintain stream flows, and to replenish aquifers. In the Middle East, countries in coastal areas also practice desalination. Desalination involves the reduction of the mineral content by taking salt out of seawater and brackish water to produce freshwater. Recent advances in technology have made process more accessible and cost-efficient, which have allowed many countries to adapt the method. On a management level, policies and laws are crafted to protect and better manage water resources, In most continental areas, the water resources span across national boundaries. Thus, interregional and international policies should be implemented to better manage resources. For example, the Amazon Cooperation Treaty Organization (ACTO) was formed to protect and manage the Amazon Basin. Member countries included Bolivia, Brazil, Ecuador, Guyana, Peru, Suriname, and Valenzuela. In the Philippines, several laws and regulations have been enacted for the protection, conservation, and management of freshwater resources. 1. Presidential Decree (PD) No. 424 of 1974 created the National Water Resources Council (NWRC) to coordinate and integrate water resources development. 2. PD No. 1067 (1976) instituted the Water Code which consolidated the laws governing the ownership, appropriation, utilization, exploitation, development, conservation, and protection of the water resources subject to regulation by the NWRC. 3. Executive Order (EO) No. 222 of 1995 established the Presidential Committee on Water Conservation and Demand Management which was tasked to prepare a nationwide Water Conservation Plan. 4. Republic Act (RA) No. 8041 or the National Water Crisis Act of 1995 addressed the country's water problems through an integrated water management program and development of new water resources and conservation of identified watersheds, among other provisions. 5. The Philippine Clean Water Act of 2004 also provided a comprehensive water quality management. Aside from these various laws, local city and municipal ordinances are also created for the specific water resources conservation and protection. The full implementation of these laws by concerned authorities is crucial in the proper management and conservation of the dwindling water resources.