Soil , also commonly referred to as earth , is a mixture of organic matter , minerals , gases , liquids , and organisms that together support the life of plants and soil organisms . Some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil.
113-489: A deluge is a large downpour of rain, often a flood . The Deluge refers to the flood narrative in the biblical book of Genesis. Deluge may also refer to: Flood A flood is an overflow of water ( or rarely other fluids ) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide . Floods are of significant concern in agriculture , civil engineering and public health . Human changes to
226-449: A dam , landslide, or glacier . In one instance, a flash flood killed eight people enjoying the water on a Sunday afternoon at a popular waterfall in a narrow canyon. Without any observed rainfall, the flow rate increased from about 50 to 1,500 cubic feet per second (1.4 to 42 m /s) in just one minute. Two larger floods occurred at the same site within a week, but no one was at the waterfall on those days. The deadly flood resulted from
339-646: A flash flood . Flash floods usually result from intense rainfall over a relatively small area, or if the area was already saturated from previous precipitation. The amount, location, and timing of water reaching a drainage channel from natural precipitation and controlled or uncontrolled reservoir releases determines the flow at downstream locations. Some precipitation evaporates, some slowly percolates through soil, some may be temporarily sequestered as snow or ice, and some may produce rapid runoff from surfaces including rock, pavement, roofs, and saturated or frozen ground. The fraction of incident precipitation promptly reaching
452-515: A landslide , earthquake or volcanic eruption . Examples include outburst floods and lahars . Tsunamis can cause catastrophic coastal flooding , most commonly resulting from undersea earthquakes. The primary effects of flooding include loss of life and damage to buildings and other structures, including bridges, sewerage systems, roadways, and canals. The economic impacts caused by flooding can be severe. Every year flooding causes countries billions of dollars worth of damage that threatens
565-662: A porous phase that holds gases (the soil atmosphere) and water (the soil solution). Accordingly, soil is a three- state system of solids, liquids, and gases. Soil is a product of several factors: the influence of climate , relief (elevation, orientation, and slope of terrain), organisms, and the soil's parent materials (original minerals) interacting over time. It continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion . Given its complexity and strong internal connectedness , soil ecologists regard soil as an ecosystem . Most soils have
678-484: A tropical cyclone or an extratropical cyclone , falls within this category. A storm surge is "an additional rise of water generated by a storm, over and above the predicted astronomical tides". Due to the effects of climate change (e.g. sea level rise and an increase in extreme weather events) and an increase in the population living in coastal areas, the damage caused by coastal flood events has intensified and more people are being affected. Flooding in estuaries
791-461: A country can be lost in extreme flood circumstances. Some tree species may not survive prolonged flooding of their root systems. Flooding in areas where people live also has significant economic implications for affected neighborhoods. In the United States , industry experts estimate that wet basements can lower property values by 10–25 percent and are cited among the top reasons for not purchasing
904-538: A drainage channel has been observed from nil for light rain on dry, level ground to as high as 170 percent for warm rain on accumulated snow. Most precipitation records are based on a measured depth of water received within a fixed time interval. Frequency of a precipitation threshold of interest may be determined from the number of measurements exceeding that threshold value within the total time period for which observations are available. Individual data points are converted to intensity by dividing each measured depth by
1017-623: A dry bulk density (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm , though the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm . Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic , although fossilized soils are preserved from as far back as the Archean . Collectively the Earth's body of soil
1130-627: A few minutes for roof and parking lot drainage structures, while cumulative rainfall over several days would be critical for river basins. Water flowing downhill ultimately encounters downstream conditions slowing movement. The final limitation in coastal flooding lands is often the ocean or some coastal flooding bars which form natural lakes . In flooding low lands, elevation changes such as tidal fluctuations are significant determinants of coastal and estuarine flooding. Less predictable events like tsunamis and storm surges may also cause elevation changes in large bodies of water. Elevation of flowing water
1243-605: A few. Gastrointestinal disease and diarrheal diseases are very common due to a lack of clean water during a flood. Most of clean water supplies are contaminated when flooding occurs. Hepatitis A and E are common because of the lack of sanitation in the water and in living quarters depending on where the flood is and how prepared the community is for a flood. When floods hit, people lose nearly all their crops, livestock, and food reserves and face starvation. Floods also frequently damage power transmission and sometimes power generation , which then has knock-on effects caused by
SECTION 10
#17328453544461356-721: A home. According to the U.S. Federal Emergency Management Agency (FEMA), almost 40 percent of small businesses never reopen their doors following a flooding disaster. In the United States, insurance is available against flood damage to both homes and businesses. Economic hardship due to a temporary decline in tourism, rebuilding costs, or food shortages leading to price increases is a common after-effect of severe flooding. The impact on those affected may cause psychological damage to those affected, in particular where deaths, serious injuries and loss of property occur. Fatalities connected directly to floods are usually caused by drowning ;
1469-451: A medium for plant growth , making it a critically important provider of ecosystem services . Since soil has a tremendous range of available niches and habitats , it contains a prominent part of the Earth's genetic diversity . A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial and largely still unexplored. Soil has a mean prokaryotic density of roughly 10 organisms per gram, whereas
1582-486: A more distant point controls at higher water levels. Effective flood channel geometry may be changed by growth of vegetation, accumulation of ice or debris, or construction of bridges, buildings, or levees within the flood channel. Periodic floods occur on many rivers, forming a surrounding region known as the flood plain . Even when rainfall is relatively light, the shorelines of lakes and bays can be flooded by severe winds—such as during hurricanes —that blow water into
1695-419: A net absorption of oxygen and methane and undergo a net release of carbon dioxide and nitrous oxide . Soils offer plants physical support, air, water, temperature moderation, nutrients, and protection from toxins. Soils provide readily available nutrients to plants and animals by converting dead organic matter into various nutrient forms. Components of a silt loam soil by percent volume A typical soil
1808-549: A pH of 9, plant growth is reduced. High pH results in low micro-nutrient mobility, but water-soluble chelates of those nutrients can correct the deficit. Sodium can be reduced by the addition of gypsum (calcium sulphate) as calcium adheres to clay more tightly than does sodium causing sodium to be pushed into the soil water solution where it can be washed out by an abundance of water. There are acid-forming cations (e.g. hydronium, aluminium, iron) and there are base-forming cations (e.g. calcium, magnesium, sodium). The fraction of
1921-731: A result of a trade-off between toxicity and requirement most nutrients are better available to plants at moderate pH, although most minerals are more soluble in acid soils. Soil organisms are hindered by high acidity, and most agricultural crops do best with mineral soils of pH 6.5 and organic soils of pH 5.5. Given that at low pH toxic metals (e.g. cadmium, zinc, lead) are positively charged as cations and organic pollutants are in non-ionic form, thus both made more available to organisms, it has been suggested that plants, animals and microbes commonly living in acid soils are pre-adapted to every kind of pollution, whether of natural or human origin. In high rainfall areas, soils tend to acidify as
2034-401: A result, layers (horizons) form in the soil profile. The alteration and movement of materials within a soil causes the formation of distinctive soil horizons . However, more recent definitions of soil embrace soils without any organic matter, such as those regoliths that formed on Mars and analogous conditions in planet Earth deserts. An example of the development of a soil would begin with
2147-412: A soil can be said to be developed, and can be described further in terms of color, porosity, consistency, reaction ( acidity ), etc. Water is a critical agent in soil development due to its involvement in the dissolution, precipitation, erosion, transport, and deposition of the materials of which a soil is composed. The mixture of water and dissolved or suspended materials that occupy the soil pore space
2260-399: A soil determines its ability to supply available plant nutrients and affects its physical properties and the health of its living population. In addition, a soil's chemistry also determines its corrosivity , stability, and ability to absorb pollutants and to filter water. It is the surface chemistry of mineral and organic colloids that determines soil's chemical properties. A colloid
2373-413: A thunderstorm over part of the drainage basin, where steep, bare rock slopes are common and the thin soil was already saturated. Flash floods are the most common flood type in normally-dry channels in arid zones, known as arroyos in the southwest United States and many other names elsewhere. In that setting, the first flood water to arrive is depleted as it wets the sandy stream bed. The leading edge of
SECTION 20
#17328453544462486-520: A type of hybrid river/areal flooding can occur, known locally as "overland flooding". This is different from "overland flow" defined as "surface runoff". The Red River Valley is a former glacial lakebed, created by Lake Agassiz , and over a length of 550 mi (890 km), the river course drops only 236 ft (72 m), for an average slope of about 5 inches per mile (or 8.2 cm per kilometer). In this very large area, spring snowmelt happens at different rates in different places, and if winter snowfall
2599-472: A valence of two, converts to (40 ÷ 2) × 1 milliequivalent = 20 milliequivalents of hydrogen ion per 100 grams of dry soil or 20 meq/100 g. The modern measure of CEC is expressed as centimoles of positive charge per kilogram (cmol/kg) of oven-dry soil. Most of the soil's CEC occurs on clay and humus colloids, and the lack of those in hot, humid, wet climates (such as tropical rainforests ), due to leaching and decomposition, respectively, explains
2712-553: Is 0.04%, but in the soil pore space it may range from 10 to 100 times that level, thus potentially contributing to the inhibition of root respiration. Calcareous soils regulate CO 2 concentration by carbonate buffering , contrary to acid soils in which all CO 2 respired accumulates in the soil pore system. At extreme levels, CO 2 is toxic. This suggests a possible negative feedback control of soil CO 2 concentration through its inhibitory effects on root and microbial respiration (also called soil respiration ). In addition,
2825-603: Is a measure of the acidity or alkalinity of the soil. More precisely, it is a measure of hydronium concentration in an aqueous solution and ranges in values from 0 to 14 (acidic to basic) but practically speaking for soils, pH ranges from 3.5 to 9.5, as pH values beyond those extremes are toxic to life forms. At 25 °C an aqueous solution that has a pH of 3.5 has 10 moles H 3 O (hydronium ions) per litre of solution (and also 10 moles per litre OH ). A pH of 7, defined as neutral, has 10 moles of hydronium ions per litre of solution and also 10 moles of OH per litre; since
2938-509: Is a small, insoluble particle ranging in size from 1 nanometer to 1 micrometer , thus small enough to remain suspended by Brownian motion in a fluid medium without settling. Most soils contain organic colloidal particles called humus as well as the inorganic colloidal particles of clays . The very high specific surface area of colloids and their net electrical charges give soil its ability to hold and release ions . Negatively charged sites on colloids attract and release cations in what
3051-411: Is about 50% solids (45% mineral and 5% organic matter), and 50% voids (or pores) of which half is occupied by water and half by gas. The percent soil mineral and organic content can be treated as a constant (in the short term), while the percent soil water and gas content is considered highly variable whereby a rise in one is simultaneously balanced by a reduction in the other. The pore space allows for
3164-424: Is also a net sink of methane (CH 4 ) but a net producer of methane (a strong heat-absorbing greenhouse gas ) when soils are depleted of oxygen and subject to elevated temperatures. Soil atmosphere is also the seat of emissions of volatiles other than carbon and nitrogen oxides from various soil organisms, e.g. roots, bacteria, fungi, animals. These volatiles are used as chemical cues, making soil atmosphere
3277-405: Is also the intentional flooding of land that would otherwise remain dry. This may take place for agricultural, military, or river-management purposes. For example, agricultural flooding may occur in preparing paddy fields for the growing of semi-aquatic rice in many countries. Flooding may occur as an overflow of water from water bodies, such as a river , lake , sea or ocean. In these cases,
3390-556: Is an important characteristic of soil. This ventilation can be accomplished via networks of interconnected soil pores , which also absorb and hold rainwater making it readily available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the water-holding capacity of soils is vital for plant survival. Soils can effectively remove impurities, kill disease agents, and degrade contaminants , this latter property being called natural attenuation . Typically, soils maintain
3503-464: Is assumed acid-forming cations). Base saturation is almost in direct proportion to pH (it increases with increasing pH). It is of use in calculating the amount of lime needed to neutralise an acid soil (lime requirement). The amount of lime needed to neutralize a soil must take account of the amount of acid forming ions on the colloids (exchangeable acidity), not just those in the soil water solution (free acidity). The addition of enough lime to neutralize
Deluge - Misplaced Pages Continue
3616-414: Is called the pedosphere . The pedosphere interfaces with the lithosphere , the hydrosphere , the atmosphere , and the biosphere . Soil has four important functions : All of these functions, in their turn, modify the soil and its properties. Soil science has two basic branches of study: edaphology and pedology . Edaphology studies the influence of soils on living things. Pedology focuses on
3729-401: Is called the soil solution. Since soil water is never pure water, but contains hundreds of dissolved organic and mineral substances, it may be more accurately called the soil solution. Water is central to the dissolution , precipitation and leaching of minerals from the soil profile . Finally, water affects the type of vegetation that grows in a soil, which in turn affects the development of
3842-419: Is common when heavy flows move uprooted woody vegetation and flood-damaged structures and vehicles, including boats and railway equipment. Recent field measurements during the 2010–11 Queensland floods showed that any criterion solely based upon the flow velocity, water depth or specific momentum cannot account for the hazards caused by velocity and water depth fluctuations. These considerations ignore further
3955-493: Is commonly caused by a combination of storm surges caused by winds and low barometric pressure and large waves meeting high upstream river flows. The intentional flooding of land that would otherwise remain dry may take place for agricultural, military or river-management purposes. This is a form of hydraulic engineering . Agricultural flooding may occur in preparing paddy fields for the growing of semi-aquatic rice in many countries. Flooding for river management may occur in
4068-400: Is controlled by the geometry of the flow channel and, especially, by depth of channel, speed of flow and amount of sediments in it Flow channel restrictions like bridges and canyons tend to control water elevation above the restriction. The actual control point for any given reach of the drainage may change with changing water elevation, so a closer point may control for lower water levels until
4181-421: Is dependent on the type of parent material , the processes that modify those parent materials, and the soil-forming factors that influence those processes. The biological influences on soil properties are strongest near the surface, though the geochemical influences on soil properties increase with depth. Mature soil profiles typically include three basic master horizons: A, B, and C. The solum normally includes
4294-401: Is induced. Capillary action is responsible for moving groundwater from wet regions of the soil to dry areas. Subirrigation designs (e.g., wicking beds , sub-irrigated planters ) rely on capillarity to supply water to plant roots. Capillary action can result in an evaporative concentration of salts, causing land degradation through salination . Soil moisture measurement —measuring
4407-531: Is likely home to 59 ± 15% of the species on Earth. Enchytraeidae (worms) have the greatest percentage of species in soil (98.6%), followed by fungi (90%), plants (85.5%), and termites ( Isoptera ) (84.2%). Many other groups of animals have substantial fractions of species living in soil, e.g. about 30% of insects , and close to 50% of arachnids . While most vertebrates live above ground (ignoring aquatic species), many species are fossorial , that is, they live in soil, such as most blind snakes . The chemistry of
4520-477: Is more advanced. Most plant nutrients, with the exception of nitrogen , originate from the minerals that make up the soil parent material. Some nitrogen originates from rain as dilute nitric acid and ammonia , but most of the nitrogen is available in soils as a result of nitrogen fixation by bacteria . Once in the soil-plant system, most nutrients are recycled through living organisms, plant and microbial residues (soil organic matter), mineral-bound forms, and
4633-461: Is more significant to flooding within small drainage basins. The most important upslope factor in determining flood magnitude is the land area of the watershed upstream of the area of interest. Rainfall intensity is the second most important factor for watersheds of less than approximately 30 square miles or 80 square kilometres. The main channel slope is the second most important factor for larger watersheds. Channel slope and rainfall intensity become
Deluge - Misplaced Pages Continue
4746-409: Is referred to as cation exchange . Cation-exchange capacity is the amount of exchangeable cations per unit weight of dry soil and is expressed in terms of milliequivalents of positively charged ions per 100 grams of soil (or centimoles of positive charge per kilogram of soil; cmol c /kg ). Similarly, positively charged sites on colloids can attract and release anions in the soil, giving
4859-540: Is very little organic material. Basaltic minerals commonly weather relatively quickly, according to the Goldich dissolution series . The plants are supported by the porous rock as it is filled with nutrient-bearing water that carries minerals dissolved from the rocks. Crevasses and pockets, local topography of the rocks, would hold fine materials and harbour plant roots. The developing plant roots are associated with mineral-weathering mycorrhizal fungi that assist in breaking up
4972-554: The Second World War ). Floods are caused by many factors or a combination of any of these generally prolonged heavy rainfall (locally concentrated or throughout a catchment area), highly accelerated snowmelt , severe winds over water, unusual high tides, tsunamis , or failure of dams, levees , retention ponds , or other structures that retained the water. Flooding can be exacerbated by increased amounts of impervious surface or by other natural hazards such as wildfires, which reduce
5085-490: The aeration of the soil and the ability of water to infiltrate and to be held within the soil. Soil water content can be measured as volume or weight . Soil moisture levels, in order of decreasing water content, are saturation, field capacity , wilting point , air dry, and oven dry. Field capacity describes a drained wet soil at the point water content reaches equilibrium with gravity. Irrigating soil above field capacity risks percolation losses. Wilting point describes
5198-561: The humus form ), the copedon (in intermediary position, where most weathering of minerals takes place) and the lithopedon (in contact with the subsoil). The soil texture is determined by the relative proportions of the individual particles of sand , silt , and clay that make up the soil. The interaction of the individual mineral particles with organic matter, water, gases via biotic and abiotic processes causes those particles to flocculate (stick together) to form aggregates or peds . Where these aggregates can be identified,
5311-425: The mineralogy of those particles can strongly modify those properties. The mineralogy of the finest soil particles, clay, is especially important. Large numbers of microbes , animals , plants and fungi are living in soil. However, biodiversity in soil is much harder to study as most of this life is invisible, hence estimates about soil biodiversity have been unsatisfactory. A recent study suggested that soil
5424-562: The water table is shallow, such as a floodplain , or from intense rain from one or a series of storms . Infiltration also is slow to negligible through frozen ground, rock, concrete , paving, or roofs. Areal flooding begins in flat areas like floodplains and in local depressions not connected to a stream channel, because the velocity of overland flow depends on the surface slope. Endorheic basins may experience areal flooding during periods when precipitation exceeds evaporation. Floods occur in all types of river and stream channels, from
5537-448: The A and B horizons. The living component of the soil is largely confined to the solum, and is generally more prominent in the A horizon. It has been suggested that the pedon , a column of soil extending vertically from the surface to the underlying parent material and large enough to show the characteristics of all its horizons, could be subdivided in the humipedon (the living part, where most soil organisms are dwelling, corresponding to
5650-406: The acronym CROPT. The physical properties of soils, in order of decreasing importance for ecosystem services such as crop production , are texture , structure , bulk density , porosity , consistency, temperature , colour and resistivity . Soil texture is determined by the relative proportion of the three kinds of soil mineral particles, called soil separates: sand , silt , and clay . At
5763-446: The addition of any more hydronium ions or aluminum hydroxyl cations drives the pH even lower (more acidic) as the soil has been left with no buffering capacity. In areas of extreme rainfall and high temperatures, the clay and humus may be washed out, further reducing the buffering capacity of the soil. In low rainfall areas, unleached calcium pushes pH to 8.5 and with the addition of exchangeable sodium, soils may reach pH 10. Beyond
SECTION 50
#17328453544465876-687: The adverse ecological impact of the inundation. That impact may also be adverse in a hydrogeological sense if the inundation lasts a long time. Examples for uncontrolled inundations are the second Siege of Leiden during the first part of the Eighty Years' War , the flooding of the Yser plain during the First World War , and the Inundation of Walcheren , and the Inundation of the Wieringermeer during
5989-423: The amount of water damage and mold that grows after an incident. Research suggests that there will be an increase of 30–50% in adverse respiratory health outcomes caused by dampness and mold exposure for those living in coastal and wetland areas. Fungal contamination in homes is associated with increased allergic rhinitis and asthma. Vector borne diseases increase as well due to the increase in still water after
6102-452: The apparent sterility of tropical soils. Live plant roots also have some CEC, linked to their specific surface area. Anion exchange capacity is the soil's ability to remove anions (such as nitrate , phosphate ) from the soil water solution and sequester those for later exchange as the plant roots release carbonate anions to the soil water solution. Those colloids which have low CEC tend to have some AEC. Amorphous and sesquioxide clays have
6215-437: The atmosphere due to increased biological activity at higher temperatures, a positive feedback (amplification). This prediction has, however, been questioned on consideration of more recent knowledge on soil carbon turnover. Soil acts as an engineering medium, a habitat for soil organisms , a recycling system for nutrients and organic wastes , a regulator of water quality , a modifier of atmospheric composition , and
6328-426: The basic cations are forced off the soil colloids by the mass action of hydronium ions from usual or unusual rain acidity against those attached to the colloids. High rainfall rates can then wash the nutrients out, leaving the soil inhabited only by those organisms which are particularly efficient to uptake nutrients in very acid conditions, like in tropical rainforests . Once the colloids are saturated with H 3 O ,
6441-434: The deadliest floods worldwide, showing events with death tolls at or above 100,000 individuals. Floods (in particular more frequent or smaller floods) can also bring many benefits, such as recharging ground water , making soil more fertile and increasing nutrients in some soils. Flood waters provide much needed water resources in arid and semi-arid regions where precipitation can be very unevenly distributed throughout
6554-436: The dry limit for growing plants. During growing season, soil moisture is unaffected by functional groups or specie richness. Available water capacity is the amount of water held in a soil profile available to plants. As water content drops, plants have to work against increasing forces of adhesion and sorptivity to withdraw water. Irrigation scheduling avoids moisture stress by replenishing depleted water before stress
6667-806: The environment often increase the intensity and frequency of flooding. Examples for human changes are land use changes such as deforestation and removal of wetlands , changes in waterway course or flood controls such as with levees . Global environmental issues also influence causes of floods, namely climate change which causes an intensification of the water cycle and sea level rise . For example, climate change makes extreme weather events more frequent and stronger. This leads to more intense floods and increased flood risk. Natural types of floods include river flooding, groundwater flooding coastal flooding and urban flooding sometimes known as flash flooding. Tidal flooding may include elements of both river and coastal flooding processes in estuary areas. There
6780-563: The field that is intended to impede the movement of the enemy. This may be done both for offensive and defensive purposes. Furthermore, in so far as the methods used are a form of hydraulic engineering, it may be useful to differentiate between controlled inundations and uncontrolled ones. Examples for controlled inundations include those in the Netherlands under the Dutch Republic and its successor states in that area and exemplified in
6893-470: The flood process; before, during and after. During floods accidents occur with falling debris or any of the many fast moving objects in the water. After the flood rescue attempts are where large numbers injuries can occur. Communicable diseases are increased due to many pathogens and bacteria that are being transported by the water .There are many waterborne diseases such as cholera , hepatitis A , hepatitis E and diarrheal diseases , to mention
SECTION 60
#17328453544467006-492: The flood thus advances more slowly than later and higher flows. As a result, the rising limb of the hydrograph becomes ever quicker as the flood moves downstream, until the flow rate is so great that the depletion by wetting soil becomes insignificant. Coastal areas may be flooded by storm surges combining with high tides and large wave events at sea, resulting in waves over-topping flood defenses or in severe cases by tsunami or tropical cyclones. A storm surge , from either
7119-403: The floods have settled. The diseases that are vector borne are malaria , dengue , West Nile , and yellow fever . Floods have a huge impact on victims' psychosocial integrity . People suffer from a wide variety of losses and stress . One of the most treated illness in long-term health problems are depression caused by the flood and all the tragedy that flows with one. Below is a list of
7232-428: The flow rate exceeds the capacity of the river channel , particularly at bends or meanders in the waterway . Floods often cause damage to homes and businesses if these buildings are in the natural flood plains of rivers. People could avoid riverine flood damage by moving away from rivers. However, people in many countries have traditionally lived and worked by rivers because the land is usually flat and fertile . Also,
7345-641: The form of diverting flood waters in a river at flood stage upstream from areas that are considered more valuable than the areas that are sacrificed in this way. This may be done ad hoc , or permanently, as in the so-called overlaten (literally "let-overs"), an intentionally lowered segment in Dutch riparian levees, like the Beerse Overlaat in the left levee of the Meuse between the villages of Gassel and Linden, North Brabant . Military inundation creates an obstacle in
7458-519: The formation, description (morphology), and classification of soils in their natural environment. In engineering terms, soil is included in the broader concept of regolith , which also includes other loose material that lies above the bedrock, as can be found on the Moon and other celestial objects . Soil is a major component of the Earth 's ecosystem . The world's ecosystems are impacted in far-reaching ways by
7571-419: The highest AEC, followed by the iron oxides. Levels of AEC are much lower than for CEC, because of the generally higher rate of positively (versus negatively) charged surfaces on soil colloids, to the exception of variable-charge soils. Phosphates tend to be held at anion exchange sites. Iron and aluminum hydroxide clays are able to exchange their hydroxide anions (OH ) for other anions. The order reflecting
7684-632: The infiltration and movement of air and water, both of which are critical for life existing in soil. Compaction , a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms. Given sufficient time, an undifferentiated soil will evolve a soil profile that consists of two or more layers, referred to as soil horizons. These differ in one or more properties such as in their texture , structure , density , porosity, consistency, temperature, color, and reactivity . The horizons differ greatly in thickness and generally lack sharp boundaries; their development
7797-403: The land in quantities that cannot be carried within stream channels or retained in natural ponds, lakes, and human-made reservoirs . About 30 percent of all precipitation becomes runoff and that amount might be increased by water from melting snow. River flooding is often caused by heavy rain, sometimes increased by melting snow. A flood that rises rapidly, with little or no warning, is called
7910-608: The livelihood of individuals. As a result, there is also significant socio-economic threats to vulnerable populations around the world from flooding. For example, in Bangladesh in 2007, a flood was responsible for the destruction of more than one million houses. And yearly in the United States, floods cause over $ 7 billion in damage. Flood waters typically inundate farm land, making the land unworkable and preventing crops from being planted or harvested, which can lead to shortages of food both for humans and farm animals. Entire harvests for
8023-417: The location of the flood. Damage to roads and transport infrastructure may make it difficult to mobilize aid to those affected or to provide emergency health treatment. Flooding can cause chronically wet houses, leading to the growth of indoor mold and resulting in adverse health effects, particularly respiratory symptoms. Respiratory diseases are a common after the disaster has occurred. This depends on
8136-436: The loss of power. This includes loss of drinking water treatment and water supply, which may result in loss of drinking water or severe water contamination. It may also cause the loss of sewage disposal facilities. Lack of clean water combined with human sewage in the flood waters raises the risk of waterborne diseases , which can include typhoid , giardia , cryptosporidium , cholera and many other diseases depending upon
8249-429: The negatively charged colloids resist being washed downward by water and are out of reach of plant roots, thereby preserving the soil fertility in areas of moderate rainfall and low temperatures. There is a hierarchy in the process of cation exchange on colloids, as cations differ in the strength of adsorption by the colloid and hence their ability to replace one another ( ion exchange ). If present in equal amounts in
8362-412: The negatively-charged soil colloid exchange sites (CEC) that are occupied by base-forming cations is called base saturation . If a soil has a CEC of 20 meq and 5 meq are aluminium and hydronium cations (acid-forming), the remainder of positions on the colloids ( 20 − 5 = 15 meq ) are assumed occupied by base-forming cations, so that the base saturation is 15 ÷ 20 × 100% = 75% (the compliment 25%
8475-419: The next larger scale, soil structures called peds or more commonly soil aggregates are created from the soil separates when iron oxides , carbonates , clay, silica and humus , coat particles and cause them to adhere into larger, relatively stable secondary structures. Soil bulk density , when determined at standardized moisture conditions, is an estimate of soil compaction . Soil porosity consists of
8588-472: The ocean has no more than 10 prokaryotic organisms per milliliter (gram) of seawater. Organic carbon held in soil is eventually returned to the atmosphere through the process of respiration carried out by heterotrophic organisms, but a substantial part is retained in the soil in the form of soil organic matter; tillage usually increases the rate of soil respiration , leading to the depletion of soil organic matter. Since plant roots need oxygen, aeration
8701-635: The other cations more weakly bound to colloids are pushed into solution as hydrogen ions occupy exchange sites ( protonation ). A low pH may cause the hydrogen of hydroxyl groups to be pulled into solution, leaving charged sites on the colloid available to be occupied by other cations. This ionisation of hydroxy groups on the surface of soil colloids creates what is described as pH-dependent surface charges. Unlike permanent charges developed by isomorphous substitution , pH-dependent charges are variable and increase with increasing pH. Freed cations can be made available to plants but are also prone to be leached from
8814-457: The period of time between observations. This intensity will be less than the actual peak intensity if the duration of the rainfall event was less than the fixed time interval for which measurements are reported. Convective precipitation events (thunderstorms) tend to produce shorter duration storm events than orographic precipitation. Duration, intensity, and frequency of rainfall events are important to flood prediction. Short duration precipitation
8927-492: The plant roots release hydrogen ions to the solution. CEC is the amount of exchangeable hydrogen cation (H ) that will combine with 100 grams dry weight of soil and whose measure is one milliequivalents per 100 grams of soil (1 meq/100 g). Hydrogen ions have a single charge and one-thousandth of a gram of hydrogen ions per 100 grams dry soil gives a measure of one milliequivalent of hydrogen ion. Calcium, with an atomic weight 40 times that of hydrogen and with
9040-486: The porous lava, and by these means organic matter and a finer mineral soil accumulate with time. Such initial stages of soil development have been described on volcanoes, inselbergs, and glacial moraines. How soil formation proceeds is influenced by at least five classic factors that are intertwined in the evolution of a soil: parent material, climate, topography (relief), organisms, and time. When reordered to climate, relief, organisms, parent material, and time, they form
9153-414: The processes carried out in the soil, with effects ranging from ozone depletion and global warming to rainforest destruction and water pollution . With respect to Earth's carbon cycle , soil acts as an important carbon reservoir , and it is potentially one of the most reactive to human disturbance and climate change . As the planet warms, it has been predicted that soils will add carbon dioxide to
9266-414: The rate of diffusion of gases into and out of soil. Platy soil structure and soil compaction (low porosity) impede gas flow, and a deficiency of oxygen may encourage anaerobic bacteria to reduce (strip oxygen) from nitrate NO 3 to the gases N 2 , N 2 O, and NO, which are then lost to the atmosphere, thereby depleting the soil of nitrogen, a detrimental process called denitrification . Aerated soil
9379-569: The result of sustained rainfall, rapid snow melt, monsoons , or tropical cyclones . However, large rivers may have rapid flooding events in areas with dry climates, since they may have large basins but small river channels, and rainfall can be very intense in smaller areas of those basins. In extremely flat areas, such as the Red River Valley of the North in Minnesota , North Dakota , and Manitoba ,
9492-480: The risks associated with large debris entrained by the flow motion. Floods can be a huge destructive power. When water flows, it has the ability to demolish all kinds of buildings and objects, such as bridges, structures, houses, trees, and cars. Economical, social and natural environmental damages are common factors that are impacted by flooding events and the impacts that flooding has on these areas can be catastrophic. There have been numerous flood incidents around
9605-454: The rivers provide easy travel and access to commerce and industry. Flooding can damage property and also lead to secondary impacts. These include in the short term an increased spread of waterborne diseases and vector-bourne disesases , for example those diseases transmitted by mosquitos. Flooding can also lead to long-term displacement of residents. Floods are an area of study of hydrology and hydraulic engineering . A large amount of
9718-442: The seat of interaction networks playing a decisive role in the stability, dynamics and evolution of soil ecosystems. Biogenic soil volatile organic compounds are exchanged with the aboveground atmosphere, in which they are just 1–2 orders of magnitude lower than those from aboveground vegetation. Humans can get some idea of the soil atmosphere through the well-known 'after-the-rain' scent, when infiltering rainwater flushes out
9831-497: The shore areas. Extreme flood events often result from coincidence such as unusually intense, warm rainfall melting heavy snow pack, producing channel obstructions from floating ice, and releasing small impoundments like beaver dams. Coincident events may cause extensive flooding to be more frequent than anticipated from simplistic statistical prediction models considering only precipitation runoff flowing within unobstructed drainage channels. Debris modification of channel geometry
9944-538: The smallest ephemeral streams in humid zones to normally-dry channels in arid climates to the world's largest rivers. When overland flow occurs on tilled fields, it can result in a muddy flood where sediments are picked up by run off and carried as suspended matter or bed load . Localized flooding may be caused or exacerbated by drainage obstructions such as landslides , ice , debris , or beaver dams. Slow-rising floods most commonly occur in large rivers with large catchment areas . The increase in flow may be
10057-441: The soil anion exchange capacity. The cation exchange, that takes place between colloids and soil water, buffers (moderates) soil pH, alters soil structure, and purifies percolating water by adsorbing cations of all types, both useful and harmful. The negative or positive charges on colloid particles make them able to hold cations or anions, respectively, to their surfaces. The charges result from four sources. Cations held to
10170-538: The soil by volatilisation (loss to the atmosphere as gases) or leaching. Soil is said to be formed when organic matter has accumulated and colloids are washed downward, leaving deposits of clay, humus , iron oxide , carbonate , and gypsum , producing a distinct layer called the B horizon. This is a somewhat arbitrary definition as mixtures of sand, silt, clay and humus will support biological and agricultural activity before that time. These constituents are moved from one level to another by water and animal activity. As
10283-420: The soil solution composition (attenuate changes in the soil solution) as soils wet up or dry out, as plants take up nutrients, as salts are leached, or as acids or alkalis are added. Plant nutrient availability is affected by soil pH , which is a measure of the hydrogen ion activity in the soil solution. Soil pH is a function of many soil forming factors, and is generally lower (more acidic) where weathering
10396-402: The soil solution. Both living soil organisms (microbes, animals and plant roots) and soil organic matter are of critical importance to this recycling, and thereby to soil formation and soil fertility . Microbial soil enzymes may release nutrients from minerals or organic matter for use by plants and other microorganisms, sequester (incorporate) them into living cells, or cause their loss from
10509-473: The soil voids are saturated with water vapour, at least until the point of maximal hygroscopicity , beyond which a vapour-pressure deficit occurs in the soil pore space. Adequate porosity is necessary, not just to allow the penetration of water, but also to allow gases to diffuse in and out. Movement of gases is by diffusion from high concentrations to lower, the diffusion coefficient decreasing with soil compaction . Oxygen from above atmosphere diffuses in
10622-430: The soil water solution will be insufficient to change the pH, as the acid forming cations stored on the soil colloids will tend to restore the original pH condition as they are pushed off those colloids by the calcium of the added lime. The resistance of soil to change in pH, as a result of the addition of acid or basic material, is a measure of the buffering capacity of a soil and (for a particular soil type) increases as
10735-433: The soil water solution: Al replaces H replaces Ca replaces Mg replaces K same as NH 4 replaces Na If one cation is added in large amounts, it may replace the others by the sheer force of its numbers. This is called law of mass action . This is largely what occurs with the addition of cationic fertilisers ( potash , lime ). As the soil solution becomes more acidic (low pH , meaning an abundance of H ),
10848-462: The soil where it is consumed and levels of carbon dioxide in excess of above atmosphere diffuse out with other gases (including greenhouse gases ) as well as water. Soil texture and structure strongly affect soil porosity and gas diffusion. It is the total pore space ( porosity ) of soil, not the pore size, and the degree of pore interconnection (or conversely pore sealing), together with water content, air turbulence and temperature, that determine
10961-502: The soil, a complex feedback which is exemplified in the dynamics of banded vegetation patterns in semi-arid regions. Soils supply plants with nutrients , most of which are held in place by particles of clay and organic matter ( colloids ) The nutrients may be adsorbed on clay mineral surfaces, bound within clay minerals ( absorbed ), or bound within organic compounds as part of the living organisms or dead soil organic matter. These bound nutrients interact with soil water to buffer
11074-414: The soil, possibly making the soil less fertile. Plants are able to excrete H into the soil through the synthesis of organic acids and by that means, change the pH of the soil near the root and push cations off the colloids, thus making those available to the plant. Cation exchange capacity is the soil's ability to remove cations from the soil water solution and sequester those to be exchanged later as
11187-409: The strength of anion adhesion is as follows: The amount of exchangeable anions is of a magnitude of tenths to a few milliequivalents per 100 g dry soil. As pH rises, there are relatively more hydroxyls, which will displace anions from the colloids and force them into solution and out of storage; hence AEC decreases with increasing pH (alkalinity). Soil reactivity is expressed in terms of pH and
11300-527: The supply of vegetation that can absorb rainfall. During times of rain, some of the water is retained in ponds or soil, some is absorbed by grass and vegetation, some evaporates, and the rest travels over the land as surface runoff . Floods occur when ponds, lakes, riverbeds, soil, and vegetation cannot absorb all the water. This has been exacerbated by human activities such as draining wetlands that naturally store large amounts of water and building paved surfaces that do not absorb any water. Water then runs off
11413-440: The third most important factors for small and large watersheds, respectively. Time of Concentration is the time required for runoff from the most distant point of the upstream drainage area to reach the point of the drainage channel controlling flooding of the area of interest. The time of concentration defines the critical duration of peak rainfall for the area of interest. The critical duration of intense rainfall might be only
11526-669: The two Hollandic Water Lines , the Stelling van Amsterdam , the Frisian Water Line , the IJssel Line , the Peel-Raam Line , and the Grebbe line in that country. To count as controlled , a military inundation has to take the interests of the civilian population into account, by allowing them a timely evacuation , by making the inundation reversible , and by making an attempt to minimize
11639-491: The two concentrations are equal, they are said to neutralise each other. A pH of 9.5 has 10 moles hydronium ions per litre of solution (and also 10 moles per litre OH ). A pH of 3.5 has one million times more hydronium ions per litre than a solution with pH of 9.5 ( 9.5 − 3.5 = 6 or 10 ) and is more acidic. The effect of pH on a soil is to remove from the soil or to make available certain ions. Soils with high acidity tend to have toxic amounts of aluminium and manganese . As
11752-473: The void part of the soil volume and is occupied by gases or water. Soil consistency is the ability of soil materials to stick together. Soil temperature and colour are self-defining. Resistivity refers to the resistance to conduction of electric currents and affects the rate of corrosion of metal and concrete structures which are buried in soil. These properties vary through the depth of a soil profile, i.e. through soil horizons . Most of these properties determine
11865-553: The water content of the soil, as can be expressed in terms of volume or weight—can be based on in situ probes (e.g., capacitance probes , neutron probes ), or remote sensing methods. Soil moisture measurement is an important factor in determining changes in soil activity. The atmosphere of soil, or soil gas , is very different from the atmosphere above. The consumption of oxygen by microbes and plant roots, and their release of carbon dioxide, decreases oxygen and increases carbon dioxide concentration. Atmospheric CO 2 concentration
11978-487: The water overtops or breaks levees , resulting in some of that water escaping its usual boundaries. Flooding may also occur due to an accumulation of rainwater on saturated ground. This is called an areal flood . The size of a lake or other body of water naturally varies with seasonal changes in precipitation and snow melt. Those changes in size are however not considered a flood unless they flood property or drown domestic animals . Floods can also occur in rivers when
12091-515: The waters in a flood are very deep and have strong currents . Deaths do not just occur from drowning, deaths are connected with dehydration , heat stroke , heart attack and any other illness that needs medical supplies that cannot be delivered. Injuries can lead to an excessive amount of morbidity when a flood occurs. Injuries are not isolated to just those who were directly in the flood, rescue teams and even people delivering supplies can sustain an injury. Injuries can occur anytime during
12204-461: The weathering of lava flow bedrock, which would produce the purely mineral-based parent material from which the soil texture forms. Soil development would proceed most rapidly from bare rock of recent flows in a warm climate, under heavy and frequent rainfall. Under such conditions, plants (in a first stage nitrogen-fixing lichens and cyanobacteria then epilithic higher plants ) become established very quickly on basaltic lava, even though there
12317-476: The whole soil atmosphere after a drought period, or when soil is excavated, a bulk property attributed in a reductionist manner to particular biochemical compounds such as petrichor or geosmin . Soil particles can be classified by their chemical composition ( mineralogy ) as well as their size. The particle size distribution of a soil, its texture, determines many of the properties of that soil, in particular hydraulic conductivity and water potential , but
12430-450: The world which have caused devastating damage to infrastructure, the natural environment and human life. Floods can have devastating impacts to human societies. Flooding events worldwide are increasing in frequency and severity, leading to increasing costs to societies. Catastrophic riverine flooding can result from major infrastructure failures, often the collapse of a dam . It can also be caused by drainage channel modification from
12543-557: The world's population lives in close proximity to major coastlines , while many major cities and agricultural areas are located near floodplains . There is significant risk for increased coastal and fluvial flooding due to changing climatic conditions. Floods can happen on flat or low-lying areas when water is supplied by rainfall or snowmelt more rapidly than it can either infiltrate or run off . The excess accumulates in place, sometimes to hazardous depths. Surface soil can become saturated, which effectively stops infiltration, where
12656-449: The year and kills pests in the farming land. Freshwater floods particularly play an important role in maintaining ecosystems in river corridors and are a key factor in maintaining floodplain biodiversity . Flooding can spread nutrients to lakes and rivers, which can lead to increased biomass and improved fisheries for a few years. Soil Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as
12769-765: Was heavy, a fast snowmelt can push water out of the banks of a tributary river so that it moves overland, to a point further downstream in the river or completely to another streambed. Overland flooding can be devastating because it is unpredictable, it can occur very suddenly with surprising speed, and in such flat land it can run for miles. It is these qualities that set it apart from simple "overland flow". Rapid flooding events, including flash floods , more often occur on smaller rivers, rivers with steep valleys, rivers that flow for much of their length over impermeable terrain, or normally-dry channels. The cause may be localized convective precipitation (intense thunderstorms ) or sudden release from an upstream impoundment created behind
#445554