WATERSHED MIDTERM NOTES.pdf

A watershed is: land on three sides. The opening A topographically delineated area of toward the sea is called the mouth of land from which rainwater can drain as the fjord, and is often shallow. The surface's-off , via a specific stream or fjor...

A watershed is: land on three sides. The opening A topographically delineated area of toward the sea is called the mouth of land from which rainwater can drain as the fjord, and is often shallow. The surface's-off , via a specific stream or fjord's inner part is called the sea river system to a common outlet point bottom. which may be a dam, irrigation system, or municipal water supply take off point, A watershed is: or where the stream/river discharges Water enters as precipitation and into a larger river, lake or the sea. leaves it as runoff and streamflow. Part A discrete geographical unit capable of of the water is stored in the soil profile providing water, timber and non-timber the excess of which is drained from it by products including food, fiber, minerals, percolation and seepage; other is medicine and many intangible goods released back to the atmosphere such as aesthetics and wholesome through evapotranspiration. environment with solar radiation, Watersheds vary greatly in size and precipitation, land, labor and capital as often extend over the boundaries of one major inputs. or more political administrative units. Malthusian vs Cornucopian perspectives on watershed resource Watershed as an Ecosystem uses, economics,and population growth Watershed is considered an ecosystem for having resources that A watershed is: are interrelated and interdependent Not necessarily an upland or among each other. mountainous land form; it may also These resources are as follows: occur in a lowland setting, and the land – Man-the manager, occupant, user, surface may be a major site for developer residential, commercial, industrial, – Timber-the wood-producing resource agricultural, educational, experimental, – Forage-the beneficial floral group of environmental and forest land uses. grassland ecosystem for animal Many of these uses are often production conflicting and competing with each – Soil-the growing medium of vegetation other for the limited watershed land and storage of water for plant and resource. animal uses A major source of nutrients and pollutants which are deposited in lakes, Watershed Characteristics coastal areas, lowland plains and rivers. Topography or Land Form-is the Is a land area drained by a stream or a general configuration of the land surface fixed body of water and its tributaries including relief and slope gradient. having a common outlet for surface – usually described as level, undulating runoff to rolling and mountainous Is a body of land bounded by ridge – is governed by the geologic nature of known as topographic divide and the underlying rocks and the relative below by phreatic divide which is the resistance of the overlying strata to level at which the water drains from the erosion. surface Synonymous to catchments, drainage Topography basin, or river basin – Anticlines-a bent or curved fold of stratified rock with the convex side up Howe sound? – Synclines- a curved fold of stratified Howe Sound (French: Baie (de) Howe) rock with the central part down and the is a roughly triangular sound, or more sides rising upward and outward in precisely a network of fjords situated opposite directions immediately northwest of Vancouver. – these anticlines and synclines are A fjord is a deep, narrow and responsible for the elongated sea or lakedrain, with steep division of an area into catchments and – Stream Density-is the number of accompanying drainage patterns. streams per unit area – land form also influences surface runoff and Streamflow A low bifurcation ratio means a higher risk of flooding. Values ranging from 3 to Watershed Ecosystem 5 indicate a natural drainage system –Climate-potential atmospheric that formed in a homogeneous rock. resource influencing the existence of other watershed resources Watershed Characteristics – Water-the life-blood of other resource Classification of drainage pattern: – Farmlands-sites of agricultural – Treelike or dendretic pattern- is a production activities well-integrated pattern formed by a main – Settlements-the population centers stream with its tributaries branching and – Animals-like man are also consumers re-branching in all directions. Such of other resources, particularly plants pattern implies that the initial slope of the area is rather flat and that the area Watershed Characteristics is composed of relatively uniform materials. Aspect-is the direction of exposure of a particular portion of a slope, Drainage Pattern expressed in azimuth (0-3600), compass bearing (e.g. N470E), or the Rectangular pattern- in areas where a principal compass points (N, NE, etc) tree like pattern prevails over a broad region but is influenced locally by faults, Orientation-is the general direction of joints, or fold of rocks, a rectangular the main stem of the stream on the pattern characterized by many abrupt watershed. A watershed with an east- bends in the streams is developed west orientation is likely to have slopes that are predominantly north and south Watershed Characteristics in aspect. – is influenced by synclines and Disordered or deranged pattern-this anticlines shows great irregularity of drainage channels and the confused intermingling Watershed Characteristics of swamps, lakes and marshes. Such – the hydrological significance of aspect drainage is common in glaciated regions. is associated with runoff and streamflow. The pattern may be treelike locally; Because of the influencing roles of modification by glacial deposition temperature on evapotranspiration, low- accounts for the haphazard energy recipient catchments generally arrangement. yield much water than high energy recipient catchments. Parallel pattern-the streams are – reverse of this observation may roughly parallel to each other. These happen in temperate areas where paralleling streams flow toward the rainfall is negligible and runoff is direction of the regional slope. The more primarily dependent on snow. the area slopes in one direction, the straighter and parallel are the streams Watershed Characteristics Drainage Pattern and Density Trellis Pattern- this pattern resembles – Drainage Pattern-is the arrangement the shape of the trellis that support a or formation of network of stream vine. It is characteristics of strongly channels as dictated by land form and folded or dipping rocks. geologic characteristics of the underlying materials. Watershed Characteristics – Drainage Density-is the length of drainage channel per unit area Featherlike or pinnate pattern-the crack of considerable length and tributaries are roughly parallel to each depth usually occurring from some other and the evenly spaced gullies join breaking or parting then at nearly right angles. This is modified parallel or treelike pattern. Watershed Characteristics Geology and Soils-these properties Radial pattern-this pattern is often are governed by the breakdown and likened to the spokes of a wheel. It is alteration of bedrock and parent composed of a group of channels materials and soil development originating from a high or terminating at bed rock characteristics having a low common center. Channels on something to do with the condition of isolated hills or basins also take this water resource: water yield, streamflow radial form. They are noticeable within response, subsurface flow integration small areas. and water quality may all be affected, as well as surface and mass erosion on Watershed Characteristics watersheds Exceptions- there are some situations where a watershed does not manifest Watershed Characteristics an integrated drainage or well-defined The kind of parent material underlying network of streams. the soil profile dictates the type of The absence is indicated by the vegetation that grows on the surface. following circumstances: Varied responses to the chemical and small watershed- there are land forms, physical components of the rock the surface of which is too small to material and the soil give rise to collect enough runoff to develop a different types of vegetative cover drainage pattern granular materials-the surface Types of Rocks drainage is not welldeveloped in these areas due to the permeability of the soil Igneous Rock, rock formed when molten or Watershed Characteristics partially molten material, called magma, Porous rocks-in these areas, surface cools and solidifies. Igneous rocks are water percolates down to the water one of the three main types of rocks; the table through cracks and cavities. other types are sedimentary rocks and Basaltic lava is a good example. metamorphic rocks. Soluble rocks-in limestone regions, Of the three types of rocks, only sinkholes and underground solution igneous rocks are formed from melted channels are developed to take care of material. The two most common types the runoff. Consequently, there is of igneous rocks are granite and general absence of surface drainage. basalt. Others-floodplains, lake beds, lower coastal plains, where there may be few Metamorphic Rock, type of rock surface drainage channels. formed when rocky material In them, the water table is high; the area experiences intense heat and pressure is level and relatively young. in the crust of the earth. Examples of metamorphic rocks are micaschist, Sinkhole quartzite and marble. A sinkhole is an area of ground that has no natural external surface drainage-- Metamorphic rocks form when when it rains, the water stays inside the extreme temperatures and pressures sinkhole and typically drains into the deep within the earth alter the subsurface. mineralogical or structural aspects of existing rock. Fissure is a narrow opening or  This transformation from one set of Type of streams minerals to another set of minerals in Ephemeral streams-are those which the rock is called comprise surface runoff only and which metamorphism. therefore flow only during and immediately after rainfall Sedimentary Rock, in geology, rock -no permanent or well-defined channels composed of geologically reworked -water table is always below the materials, formed by the accumulation streambed and consolidation of mineral and Intermittent Streams-are those which particulate matter deposited by the flow during the wet season but dry up action of water or, less frequently, wind during dry season or glacial ice. Perennial Streams- stream which flow throughout the year Watershed Characteristics Vegetative cover-benefits afforded by vegetation to the watershed are almost immeasurable. it serves as cover against soil erosion it prevents desiccation of soil moisture acts as filter of water reaching the streams ameliorates microclimate pumps nutrients loosens soil improving its infiltration capacity promotes or enhances biodiversity source of wood, food, clothing materials, medicine, gums, latex, resins, etc Streamflow- is the condition by which water is received, stored, and released by the watershed’s drainage channels. -its condition is expressed generally as: water regimen, water quality and water quantity -Removal of vegetation from the watersheds would affect water yield -superior quality water is expected from undisturbed forestlands Water Yield Water Quality-refers to the special property or degree of superiority of water Water Quantity-refers to the volume of discharge Water Regimen-is the seasonal variations of flow which tend to be repeated year after year