Understanding Precipitation, Runoff, and Groundwater Systems
Precipitation
Changes in air pressure and temperature associated with the movement of air masses cause air to become saturated with water vapor. This vapor then condenses around tiny particles in the air, such as pollen, dust, sea salt, and volcanic ash, leading to precipitation.
Main Controls of Atmospheric Precipitation:
- Collision of Air Masses: Most precipitation occurs when large masses of warm, moist air collide with cold air masses, such as in cyclones and hurricanes.
- Convection: Heat from the Earth’s surface causes air to rise. As this warm air rises into colder regions, it cools, and water vapor condenses, potentially leading to precipitation. This process can also be influenced by mountain ranges.
- Orographic Precipitation: This type of precipitation occurs when air masses are forced to rise over mountains or other topographic barriers. As the air rises, it cools adiabatically, leading to condensation and precipitation.
Evapotranspiration
Evapotranspiration is the combined process of evaporation from surfaces and transpiration from plants.
- Xerophytes: Desert plants like xerophytes have adapted to minimize water loss through transpiration.
- Phreatophytes: Plants like cacti (phreatophytes) thrive in dry climates by accessing deep underground water sources and transpiring large amounts of water.
Runoff
Runoff is the flow of water over the land surface and includes both surface runoff and subsurface flow that emerges at the surface.
- Surface Runoff: Occurs when precipitation exceeds the soil’s infiltration capacity.
Sources of Subsoil Water
- Precipitation
- Water drawn up from deep within the Earth through intrusive rocks
- Water trapped between sedimentary rock layers during their formation
Calculating Runoff Volume
R = P * L * G
Where:
- R = Runoff
- P = Precipitation
- L = Basin Recharge
- G = Subsoil Water Increase
All terms are measured in inches or millimeters over the drainage area. Accurate runoff estimates depend on reliable assessments of basin recharge (L) and subsoil water increase (G).
Runoff Coefficient (K)
K = R / P
Example K Values for Different Surfaces:
- Residential areas: K = 0.30
- Apartments with green spaces: K = 0.50
- Commercial and industrial areas: K = 0.90
- Forested areas (depending on soil): K = 0.05 to 0.20
- Parks, farmland, and pastures: K = 0.05 to 0.30
- Asphalt and concrete pavement: K = 0.85
Infiltration
Infiltration is the process of water moving from the surface into the soil.
- Infiltration Capacity: The maximum rate at which water can enter the soil under specific conditions.
- Infiltration Rate: The actual rate at which water enters the soil during a rainfall event. It is limited by either the infiltration capacity or the rainfall intensity, whichever is lower.
Factors Affecting Infiltration Capacity:
- Soil Texture: Loose, permeable soils have higher infiltration capacities than tight clay soils.
- Soil Moisture: Infiltration capacity is typically lower when the soil is wet compared to when it is dry.
- Subsoil Permeability: If the soil surface is saturated, the rate of water movement deeper into the ground is determined by the permeability of the underlying subsoil.
Infiltration Rate Calculation:
W = (P – R) / Tr
Where:
- W = Infiltration index
- P = Precipitation
- R = Runoff
- Tr = Rainfall duration (hours)
Infiltration Coefficient (K):
K = (i – w) / i
Where:
- i = Rainfall intensity
Groundwater in Consolidated Rocks
The search begins to investigate groundwater unconsolidated sediments.
1. For ease of drilling in rocks of this type, which was reflected in the relatively low cost of observation wells.
2. Because these deposits, located in valleys where the water level is relatively near the surface and significantly reduces the pumping wells.
3. Because these deposits to be near lakes or rivers ensure a reliable load.
4. The unconsolidated sediments present specific yields much higher than any of the rocks.
5. And is that the permeability of these materials are far superior to many of the other rocks of volcanic rocks elcome, cavernous limestone.
The infiltration capacity depends on many factors including:
1 loose-permeable soil will have greater capacity than a tight clay soil.
2-if many of the pore spaces are filled with water infiltration capacity is generally lower than when the soil is relatively dry.
3-if the pore space of the soil surface is fully occupied by water, the move back below the humidity is controlled by the permeability of the subsoil.
The infiltration rate: the rate at which water enters the soil effectively during a storm or shower and should be equal to the infiltration capacity or the rhythm of the rain if either is the minimum value.
Infiltration rate: the average rate of infiltration or index “W” which can be calculated with the formula: W = (AB) / TR. Where: W = infiltration index, P = precipitation runoff R = Tr = duration of rainfall in hours is a second index which is defined poe the rhythm of the rain above which the volume of rainfall equals the volume of runoff
They say when W = È esque rain is reasonably uniform
With the data we can calculate the infiltration of runoff coefficient K = (iw) / i where i = rainfall intensidada
Aquifer = are the formations that contain and transmit groundwater capacity is measured by the porosity which is determined by drying in the oven and one undisturbed by weighing muesrtra
Acuifuga = is a rock that transmits or stores water or
Acuicluido = rock that stores water but transmits
Aquitard = transmits and stores water but not enough to meet the individual sediment
Aquifers include: unconsolidated sediments, fracture zones in plutonic rocks, porous layers of sandstone, limestone caverns and so on.
The specific yield is the volume of water expressed by a percentage of total volume of aquifer that drains freely from the aquifer
CAPA O Pit: This is the static level of water in wells that penetrate the saturated zone
Confined water: The water that is separated from the atmosphere by an impermeable material
SEMICONFINADA WATER: It is a middle ground.
HANGING WATERS: This is the first free water, found on the regional water table area and a single body whose position is controlled by structures and stratigraphy.
Unconfined OR FREE WATER: The water that is in direct contact with the lees THROUGH admosfera and open spaces in porous materials.
MAP WATER LEVEL: The water levels measured in the sediment is easily studied by means of maps of curves that level, which are named after isofreaticas in the event that these levels belong to free aquifers or water tables or een oisopresas represent cases of what are piesometricos level of confined aquifers, the direction of flow dgeneral groundwater can be shown on maps either isofreaticas or isopresa.
The flow network can be used to find areas of recharge or discharge, they pretended to calculate the amount of water flow Subterrania.
DOWNLOAD THE UNDERGROUND WATER: The ground water in excess of local capacity of an aquifer is discharged through evapotranspiration and surface discharge when the cord reaches capillary root systems of vegetation, provides a direct route to direct perspiration toward the adtmosfera.
THE THREE Prinsipal variables which determine a SPRING ARE:
1. The permiavilidad the aquifer.
2. The area available to recharge the aquifer.
3. The amount of that charge.
Variability of a source can be expressed as:
VARIABILITY = Qmax-Qmin x 100
Q Media
Where
Qmax = maximum flow measured
Qmin = minimum measured
QMedia = average flow measured
These observations are made THROUGH whole hydrological year, ie from the dry season picks up at the end of next season, this variability index indicates a lot about the confidence that can be a particular source of perennial water source.
Download artificial is done by means of wells, which are studied elsewhere.
Subterrania waters in igneous and metamorphic rocks; the extremities variations in lithological and structural features in volcanic terrains make the Subterrania locañizacion water in volcanic rocks are very difficult, as well as vegetation cover, and very often volcanic senis thickness grades are detailed study of outcrops and quite difficult geological map igneous and metamorphic rocks and plutonic solid fragments of such rocks may have porosities vagisimas for example 3% and 1% even more successful and more. These wells are generally not interconnected, as results, permanialidad a fracmento of these may be considered equal to sero, however, long body formed by boulder developed high porosity can see devido a fracturing processes and metiorisacion.
Volcanic rocks: between this type of rock changes in hydrogeological properties are very large. Some vasaltos presented transmisilidades lava and near the highest known, and most of the tuffs, although they present very high porosities can be categorized as virtually impermeable.
Groundwater in consolidated sedimentary rocks: sedimentary rocks between the very different shape types can find other characters as well pretrograficas varied hidrogealogicas however, the geological knowledge of the given region can give valuable guidelines on the presence of groundwater in these rocks classes.
Sandstone: the porosities in the sandstones vary vastante, from less than 1% to over 30%. This porosity will depend on the selection, enpaquetamineto, a uy sementacion degree of which is the most important.
The most common materials are:
Arsilla, calsitas, dolomite and silica (quartz)
Carbonate rocks: limestones and dolomites are the two most common types of carbonate rocks. Its origin can be varied eg some from clay deposits of inorganic precipitation or accumulation of skeletons of microscopic or unicellular organisms that make up the seedlings in the seas. This rock in its original form relatively dense and compact.