Forest hydrology

Forest hydrology combines aspects of two separate disciplines: hydrology and forestry. Hydrology is the science that studies the waters of Earth. Hydrology seeks to understand where water occurs; how water circulates; how and why water distribution changes over time; the chemical and physical properties of water; and the relation of water to living organisms

Forests and the Hydrologic Cycle.

The surface water in a stream, lake, or wetland is most commonly precipitation that has run off the land or flowed through topsoils to subsequently enter the water body. If a surficial aquifer is present and hydraulically connected to a surface-water body, the aquifer can sustain surface flow by releasing water to it.In general, a heavy rainfall causes a temporary and relatively rapid increase in streamflow due to surface runoff. This increased flow is followed by a relatively slow decline back to baseflow, which is the amount of streamflow derived largely or entirely from groundwater. During long dry spells, streams with a baseflow component will keep flowing, whereas streams relying totally on precipitation will cease flowing. Generally speaking, a natural, expansive forest environment can enhance and sustain relationships in the water cycle because there are less human modifications to interfere with its components. A forested watershed helps moderate storm flows by increasing infiltration and reducing overland runoff. Further, a forest helps sustain streamflow by reducing evaporation . Forests can help increase recharge to aquifers by allowing more precipitation to infiltrate the soil, as opposed to rapidly running off the land to a downslope area.

Aquatic Biodiversity.

Forest lands and waters are vitally important in maintaining biodiversity and providing habitat for fish and wildlife, including threatened or endangered aquatic species. For aquatic species, watersheds provide the basic unit of any conservation strategy. Many watersheds also contain isolated habitats with unique characteristics producing a high potential for rare species. Some species occur only near a single spring or in a single stream within a given watershed. Lands set aside to protect these unique habitats also benefit the entire watershed and its ecosystem

Effects of Fire.

Destructive fires that remove large amounts of organic matter in a forest cause loss of nutrients from the soil as the detrital and upper soil layers are burned and eroded. Moreover, fires can adversely affect the quality of streams and lakes in the burned region as well as

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tributary watersheds downstream. Surface runoff that otherwise would have been slowed or absorbed by living and dead vegetative matter on the forest floor now runs unimpeded down bare (or nearly bare) slopes. The increased velocity carries more soil particles and loose vegetative matter downslope, along with any adsorbed nutrients.

Forest Management and Watershed Quality

Wind, fire, insects, and disease are all part of properly functioning, healthy ecosystems in watersheds. For example, natural fires, although temporarily devastating, periodically restore the balance between vegetation types, and release nutrients from the vegetation and soil. In contrast, widespread clear-cut logging and excessive or improper road-building can degrade watersheds, Rill and gully erosion caused by flowing water is evident on this steep slope following a forest fire. The soil loss can be substantial, and denuded slopes can be difficult to revegetate.As can land uses such as ski runs and housing projects. Many human activities can increase overland runoff, resulting in more erosion of the land surface and concurrently reducing the amount of water that soaks in the ground to potentially reach nearby streams or recharge underlying aquifers. Moreover, fire prevention and suppression have created "imbalanced" forests with excessive amounts of undergrowth and dead vegetative matter that serve as fuels when fire does occur. Hence, these forests are at increased risk of high-intensity, destructive fires. Watershed and restoration may include controlled thinning, prescribed burning, and other management practices to restore the proper balance of timber, undergrowth, and grassy meadows in the watershed. Restoration also may include planting of appropriate native plants.

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The Water Table

The water table is the surface where the water pressure head is equal to the atmospheric pressure . It may be conveniently visualized as the "surface" of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as surface tension holds water in some pores below atmospheric pressure. Individual points on the water table are typically measured as the elevation that the water rises to in a well screened in the shallow groundwater.

The groundwater may be from infiltrating precipitation or from groundwater flowing into the aquifer. In areas with sufficient precipitation, water infiltrates through pore spaces in the soil, passing through the unsaturated zone. At increasing depths water fills in more of the pore spaces in the soils, until the zone of saturation is reached. In permeable or porous materials, such as sands and well fractured bedrock, the water table forms a relatively horizontal plane. Below the water table, in the phreatic zone, permeable units that yield groundwater are called aquifers. The ability of the aquifer to store groundwater is dependent on the primary and secondary porosity and permeability of the rock or soil. In less permeable soils, such as tight bedrock formations and historic lakebed deposits, the water table may be more difficult to define.

The water table should not be confused with the water level in a deeper well. If a deeper aquifer has a lower permeable unit that confines the upward flow, then the water level in a well screened in this aquifer may rise to a level that is greater or less than the elevation of the actual water table. The elevation of the water in this deeper well is dependent upon the pressure in the deeper aquifer and is referred to as the potentiometric surface, not the water table.[1]

Figure 1 showing different zones of the subsurface

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Impurities in Well Water

Because aluminum is so pervasive in the environment, to the point of being unavoidable, researchers have long been studying its effects on humans. This research has revealed a link between aluminum intake and neurological dementia in kidney dialysis patients In recent years, the public and the media have become concerned about other possible adverse effects of aluminum on human health, including its role in Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis (Lou Gehrig's disease). In addition, questions have been raised about the potential risks to infants who drink baby formula containing aluminum.

Arsenic Most arsenic enters water supplies either from natural deposits in the earth or from industrial and agricultural pollution. Arsenic is a natural element of the earth's crust. It is used in industry and agriculture, and for other purposes. It also is a byproduct ofcopper smelting, mining and coal burning. U.S. industries release thousands of poundsof arsenic into the environment every year.According to a 1999 study by the National Academy of Sciences, arsenic in drinking water causes bladder, lung and skin cancer, and may cause kidney and liver cancer. The study also found that arsenic harms the central and peripheral nervous systems, as well as heart and blood vessels, and causes serious skin problems. It

Cadmium Cadmium is released into the environment from mining and metal processing operations, burning fuels, making and using phosphate fertilizers, and disposing of metal products. Cadmium is not mined, but it is a by-product of the smelting of other metals such as zinc, lead, and copper. Cadmium is used in nickel-cadmium rechargeable batteries and for metal plating. It also is used in some paints, plastics, and metal solders.

Cadmium is found naturally in small quantities in air, water, and soil. Since cadmium is a metal, it does not break down and can accumulate over time. Burning household or industrial waste and burning coal or oil may release cadmium into the air. Cadmium can enter the body from smoking tobacco, eating food and drinking water containing cadmium, and inhaling it from the air.

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ChlorineThe experimental use of chlorine began in the 1890's to combat water-borne diseases such as cholera and typhoid. It quickly gained wide acceptance because of low cost and high efficiency in killing just about everything hazardous in the water. Chlorine allowed population centers to spring up and thrive without any epidemic outbreaks.The problem with chlorine is that it is a known poison and the safety of drinking this poison over the long term is highly uncertain. Also, chlorine reacts with water-borne decaying organic matter like leaves, bark, sediment, etc. to create a family of chemicals called trihalomethanes and other highly toxic substances. Trihalomethanes, or THM's, include chemicals such as chloroform, bromoform and dichlorobromethane, all of which are extremely carcinogenic even in minute amounts.

CopperCopper rarely occurs naturally in water. Most copper contamination in drinking water happens in the water delivery system, as a result of corrosion of the copper pipes or fittings. Copper piping and fittings are widely used in household plumbing. Generally, naturally soft water is more corrosive than hard water because it is more acidic and has low TDS.At very high levels, copper can cause a bitter metallic taste in water and result in blue-green stains on plumbing fixtures. At low levels, copper in drinking water may cause no health symptoms. At high levels, copper in drinking water may cause symptoms easily mistaken as flu or other illnesses. Thus health symptoms are not a reliable indication of copper in drinking water.

FluorideWaters with high fluoride content are found mostly in calcium-deficient waters in many basement aquifers, such as granite and gneiss, in geothermal waters and in some sedimentary basins. Fluorides in water can be detrimental or beneficial. It all depends on the concentration. Surface water supplies are normally low in fluorides (less than 0.5 ppm). Some have no fluoride at all. Well waters may contain excessive amounts of fluoride. There are some wells which contain the recommended amount (1 mg/L) for drinking water.

LeadLead rarely occurs naturally in water. Most lead contamination takes place at some point in the water delivery system. Lead pipes and lead solder in the distribution system are the main sources of lead pollution. Boston Globe estimates that 98% of all households have lead in their plumbing. Houses older than 20 years and less than five years are most at risk. Also, houses in areas of soft (low mineral levels) water tend to corrode the lead from the pipes more easily.Lead is a cumulative toxin that stays in the tissue permanently, especially in brain tissue. It also affects a person in relation to their body weight. Therefore, an exposed adult can fend off the toxic effects for some time but in children, brain and developmental damage occur quickly and permanently.

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Magnesium Magnesium is present in all natural waters and enters the groundwater the same way as calcium by contact with rock formations. Magnesium is associated with calcium and is also a major contributor to hardness. As well, magnesium may contribute to undesirable tastes in your water if the concentration is high. When present in water with sulfates, magnesium may have a laxative effect or cause gastrointestinal irritation.

ManganeseManganese is a mineral that naturally occurs in rocks and soil and is a normal constituent of the human diet. It exists in well water as a groundwater mineral, but may also be present due to underground pollution sources. You may suspect that manganese is in your water if the water is discolored (brownish-red), causes staining of plumbing fixtures or clothing or has an off-taste or odor. Exposure to high concentrations of manganese over the course of years has been associated with toxicity to the nervous system, producing a syndrome that resembles Parkinson Disease.

SodiumSodium is a naturally occurring mineral which is found in water sources. While sodium is not regulated as a contaminant in drinking water, it may have an effect on the consumer's health. In general, the sodium contributed to an individual's diet from drinking water is a small part of overall dietary intake. The American Heart Association's recommended standard for daily sodium intake is 3,000 milligrams. Persons on severely restricted sodium diets may want to consult their health professional regarding sodium levels in water. Water softeners can add sodium to your household water supply as well.

ZincZinc occurs naturally, most zinc finds its way into the environment because of human activities. Mining, smelting metals (like zinc, lead and cadmium) and steel production, as well as burning coal and certain wastes can release zinc into the environment. Zinc is frequently used as a protection to “galvanize” steel. When high levels of zinc are present in soils, such as at a hazardous waste site, the metal can seep into the groundwater. Zinc can enter the body if you eat foods or drink water or other beverages containing zinc, or if you breathe zinc dust or fumes from the air. Very small amounts of zinc enter the body through skin contact. Foods naturally contain zinc but vary greatly in their zinc content. Very small amounts of the zinc in food are absorbed by the body. Drinking beverages stored in metal cans or drinking water that flows through metal pipes coated with zinc also are sources of zinc exposure.

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Drilled Wells vs Dug Wells

Drilled Wells

Casing on drilled domestic wells generally have a diameter of 4–8 in (most commonly 6 inches in newer wells)A drilled well consists of a hole bored into the ground, with the upper part being lined with casing. The casing prevents the collapse of the borehole walls and (with a drive shoe or grout seal) to prevent surface or subsurface contaminants from entering the water supply and a well screen is placed at the bottom of the well to prevent inflow of sediment into the pump. The casing also provides housing for a pumping mechanism and for the pipe that moves water from the pump to the surface. Drilled wells are constructed by either percussion or rotary-drilling machines. A well that is constructed with a rotary drilling machine incorporates the use of circulating drilling fluid or compressed air to remove drill cuttings from the well hole. To serve as a water supply, a drilled well must intersect bedrock fractures containing ground water.Most modern wells are drilled, which requires a fairly complicated and expensive drill rig. Drill rigs are often mounted on big trucks. They use rotary drill bits that chew away at the rock, percussion bits that smash the rock, or, if the ground is soft, large auger bits. Drilled wells can be drilled more than 1,000 feet deep but domestic wells are usually between 100-200 feet in depth and 6 inches in diameter. Often a pump is placed near the bottom to push water up to the surface.

Dug Wells

Casing on dug wells generally have a diameter of 60–120 cm (24–48 in) .Dug wells are holes in the ground dug by shovel or backhoe. Historically, a dug well was excavated below the groundwater table until incoming water exceeded the digger’s bailing rate. The well was then lined (cased) with stones, brick, tile, or other material to prevent collapse. It was covered with a cap of wood, stone, or concrete. Today, there are specific requirements for casing materials. For more information on the construction requirements of a dug well, please see the Water Well Regulation. Since it’s so difficult to dig beneath the ground water table, dug wells are not very deep. Typically, they are only 10 to 30 feet deep and 1 meter in diameter. Being so shallow, dug wells have the highest risk of becoming contaminated and they often go dry during periods of drought if the water table becomes lower than the depth of the well.

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Figure 3 showing components of a drilled well

Figure 4 showing components of a dug well

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References

http://www2.gnb.ca/content/dam/gnb/Departments/env/pdf/Water-Eau/WellWaterBasics.pdf

http://www.demiwater.nl/files/AWT_IMPURITIES_IN_WATER.pdf

http://www.triumvirate.com/engineering-blog/bid/24742/Sources-of-groundwater-contamination

http://water.usgs.gov/edu/earthgwaquifer.html

http://www.excelwater.com/eng/b2c/impurities.php

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