EAST MESA WATERSHED STUDY

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EAST MESAWATERSHED STUDY

• Definitions

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Hydrology and Hydraulics

• Hydrology - The study of the properties, movement
  and behavior of water on the land surface and
  under ground. Hydrology deals with where and how
  much water there is, where it came from, and
  where it is going.
• Hydraulics - The study of the properties,
  movement and behavior of water flowing in open
  channels or pipes.

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Watershed

• Watershed - Area that drains to a common
  outlet. For a river or stream, it is all the
  land that drains to it or its tributaries.
  Variously called Basin, Drainage Basin or
  Catchment. A Sub-basin or Subwatershed is a
  discriminate drainage basin within a larger
  watershed, typically defined for planning or
  modeling purposes. The size of a watershed is
  known as its Drainage Area.

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Geomorphology

• Geomorphology - A branch of geology that deals
  with the form of the earth, the general
  configuration of its surface, and the changes
  that take place due to erosion of the primary
  elements and the buildup of erosional debris.
• Fluvial Geomorphology - deals with how a stream
  or river changes the configuration of the earth
  by eroding its banks and streambed and
  transporting sediment from one location to
  another.
• Channel Forming Flows - also described as the
  dominant, effective, or bankfull discharge.
  This is the amount of flow in a channel that
  causes the most geomorphic change over time..

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Geomorphology

• Erosion - Wearing away of rock or soil by the
  gradual detachment of soil or rock fragments by
  water, wind, ice, and other mechanical, chemical,
  or biological forces. In a stream, the soil is
  removed from the banks and bed of the stream.
• Sedimentation Deposition of soil particles. As
  sediment is removed from one part of a stream by
  erosive forces, it is deposited at another part
  of the stream. Usually the sediment is deposited
  at a slower moving area, causing the stream bed
  to build up at this location.
• Downcutting The process by which a streams bed
  is lowered over time through erosion of the beds
  material. Also known as channel degradation.

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Geomorphology

• Aggradation The process by which a streams bed
  raises over time through the deposition of
  additional sediment to its bed.
• Cutbanks A steep bank caused by erosion,
  usually on the outside of a river bend. As the
  stream erodes material at the base or toe of
  the bank slope, material above it falls into the
  stream. Over time the outside edge of the stream
  moves, or meanders, farther into the bank.
• Incised Channel - A stream that, through
  degradation, has cut its channel into the bed of
  the stream valley.

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Geomorphology

• Clear Water Scour Erosion of a streams bed and
  banks caused by large clear water flows. Clear
  water is water that carries little sediment, thus
  it has the ability to carry more bed and bank
  material from an area and lacks the sediment load
  to replace what it removes. Clear water can also
  come from developed areas with mostly impermeable
  area.
• Headcutting - The process by which the channel is
  actively eroding the streambed downward
  (degrading, incising, downcutting) to a new base
  level. Because of the resultant increase in
  slope, this erosional action progresses upstream.
  Drop structures are often used to stop a headcut
  from progressing upstream.

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Floodplains

• Floodplain The area outside the bank of a
  natural or artificial channel that is subject to
  flooding.

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Flooding

• Alluvial Fan -- An alluvial fan is a sedimentary
  deposit located a topographic break such as the
  base of a mountain front, escarpment, or valley
  side, that is composed of streamflow and/or
  debris flow sediments and which has the shape of
  a fan, either fully or partially extended.
• Alluvial Fan Flooding -- Flooding that occurs on
  the surface of an alluvial fan or similar
  landform. For the East Mesa, flows would
  originates at the apex of the Organ Mountains.
  This type of flooding is characterized by
  high-velocity flows active processes of erosion,
  sediment transport, and deposition and,
  unpredictable flowpaths.