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NRM 4314 Test2

# NRM 4314 Test2 - N R M 4314 Test#2 IV Hyd rologic P...

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NRM 4314 Test #2 IV. Hydrologic Processes on Watersheds A. The hydrologic cycle. This cycle may be divided into four major functional parts and expressed as an equation or model. Equation:

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P = RO + ET ± S P is precipitation RO is runoff RO = P – ET ± S ET is evaporation or transpiration S is storage B. The driving force behind the hydrologic cycle is energy derived from solar radiation. Energy balance concept: S o + T + L + G + C + S t = 0 S o = Solar radiation T = Thermal radiation L = Latent heat G = Conduction C = Convection S t = Storage Solar radiation is the primary source of input to the earth’s energy balance system. Factors decreasing amount of solar radiation received: 1. Atmosphere thickness and density 2. Atmospheric pollutants, etc. 3. Earth axis position 4. Terrain features—slope, aspect, etc. Solar radiation is short-wave. Most other, i.e. earth surface radiation, is long wave. As radiant energy strikes a surface one of three things may occur: 1. Absorption
2. Reflection 3. Transmission Albedo -reflectivity of materials very important in determining the amount of radiation absorbed by an object and its conversion to heat Absorbed energy is available to do work. As a body absorbs energy its temperature rises and it in turn radiates energy- the difference between incoming and outgoing radiation is called net radiation, and it is the energy available to do work of some kind. Specific heat -amount of heat necessary to raise 1 gram 1°C Water 1.00 Lead 0.03 Soil 0.20 Sensible heat - temperature is a measure of the quality of sensible heat; we can detect sensible heat due to temperature differences Latent heat - thermal energy which does not change the temperature of an object in a sensible fashion Sublimation - change directly from solid to vapor—total latent heat of fusion and vaporization Conduction -transfer of heat through matter by means of intermolecular contact; relatively little heat exchange occurs by conduction on watersheds due to generally low conductivities of the materials Convection - transfer of heat by mass movement of the substance containing the heat Advection - horizontal movement of heat by air mass movement from one area to another

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Generally speaking, convective heat transfer is the dominant means of energy exchange in a watershed (after radiation). Factors in convective heat transfer: 1. Wind speed of air 2. Temperature differences and vapor pressure gradients between surface and air 3. Surface roughness C. Active Surface Concept For our purposes this is the soil and vegetation cover of a particular watershed. It is primarily through modification of the active surface that we can modify the energy relationships on a watershed and thus modify the hydrologic cycle. Active surface characteristics (fixed) 1. Slope 2.
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