Term
| What are the types of evaporation from vegetation? |
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Definition
- Transpiration, Evaporation form interception, SPA (soil, plant, atmosphere)
• Transpiration – Loss of H2O from stomata, it also controls the amount released.
• Evaporation from interception is the water on the canopy.
• SPA – Atmosphere is the sink, potential evaporation, uses the air gradient.
Plant – leaf water potential, suction in the leaves, as water is released from stomata it causes a suction in the roots. |
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Term
| How does vegetation effects thermodynamic and aerodynamic forces? |
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Definition
- Albedo, turbulence and aerodynamic resistance (ra).
• Albedo – The vegetation type, what season it is, as well as dead material effect albedo of a particular area.
• Turbulence – the vegetation roughness affects turbulence.
• Aerodynamic resistance - ra = {ln[(z-d)/Zo]}² / K²U₂ |
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Term
| Explain the aerodynamic resistance equation and what it affects? |
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Definition
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Term
| How do plants control transpiration? |
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Definition
• Solar energy, H2O, photosynthesis, absorb CO2 and release H2O and O2 through stomata.
• The Stomata react to external conditions which affect transpiration.
- Stomata resistance.
• Parallel resistance, which lowers resistance. The stomata can open at different size’s which regulates the amount of transpiration.
- Canopy resistance.
• (LAI) leaf area index, leaf area per unit of ground area
• The greater the LAI the lower the resistance
• Rc α 1/LAI Increase stomata, decreases resistance; keeping stomata closed to decrease water loss. |
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Term
| Explain the evaporation of intercepted water? |
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Definition
(Timing, Rate, Snow)
- Timing – Short rain fall with clear weather a significant amount of water can evaporate.
- Rate – Evaporation will happen faster than transpiration due to the stomata. This is free water and a passive process.
- Snow – Large amounts of snow can be stored in tree canopy. An increasing amount of evaporation due to the snow sitting in the canopy.
- The total amount of evaporation from an area includes a cumulative effect from a variety of vegetation. |
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Term
| Explain the penman equation? |
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Definition
- This formula is combine energy balance equation and gradient equation with an assumption.
• The assumption is that the temperature of a wet surface and the air temperature are similar or the same.
• This formula is used when the surface is wet or water isn’t limiting.
- The Penman equation describes evaporation (E) from an open water surface, and was developed by Howard Penman in 1948. Penman's equation requires daily mean temperature, wind speed, relative humidity, and solar radiation to predict E.
- This equation was developed to remove air temperature measurements at two levels. |
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Term
| Explain the penman-monteith equation? |
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Definition
| - This equation is similar to the penman equation but it takes vegetation into account by adding canopy resistant’s. |
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Term
| Priestley-Taylor equation |
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Definition
| - This equation was developed as a substitute to the Penman–Monteith equation. For Priestley–Taylor, only radiation observations are required. This is done by removing the aerodynamic terms from the Penman–Monteith equation and adding an empirically derived constant factor, . - The underlying concept behind the Priestley–Taylor model is that an air mass moving above a vegetated area with abundant water would become saturated with water. In these conditions, the actual evapotranspiration would match the Penman rate of potential evapotranspiration. However, observations revealed that actual evaporation was 1.26 times greater than potential evaporation, and therefore the equation for actual evaporation was found by taking potential evapotranspiration and multiplying it by . The assumption here is for vegetation with an abundant water supply (i.e. the plants have low moisture stress |
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Term
| Soil moisture and soil texture |
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Definition
- The hydrological significance is it’s important for agriculture and flood prediction.
- Horizon and texture
• Horizon is the layers of the soil and texture is the size of the mineral componants (sand, silt, clay)
- The structure plays an important part in determining infiltration. Clumps of soil have more space which allows more water to follow through, while clay soil is compact and allows very little through. |
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Term
| Explain how to measure soil water content. |
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Definition
- Gravimetric is one way where you measure (H2O content/Dry Mass) usually with a clump of soil. Problems with this method is not all material can be measured this way.
- Volume metric is normally used, (volume of H2O/ Total volume)
- When measuring the soil content suction and adhesion come into play. As well as the matrix force which is the force the matrix applies. |
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Term
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Definition
- Darcy’s law is the rate of flow through a slab of soil. There are two equations for soil water movement for saturated and unsaturated conditions
- Increasing suction when soil dries out, but the gradient is usually the greater force.
- In a vertical situation gravity is always a constant. The rate of flow depends on degree of elevation and soil characteristics. |
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Term
| Explain infiltration capacity. |
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Definition
- Infiltration capacity depends on the rate of water moving across the soil and the rate of water entering the soil.
- Infiltration capacity is the maximum amount of water a soil can hold. Each soil type will have a different saturation curve.
- Variables that effect the capacity are texture (soil type), structure (big/small spaces), organic matter (increases infiltration) and frozen ground.
- Using the curve and with the rate of rain fall we can determine how much rain is going into the soil and how much is going over the top. Rain flow on the top can lead to floods and erosion. |
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Term
| Explain Stream flow and runoff |
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Definition
- Runoff is water that does not infiltrate.
- Stream flow (aka discharge, river flow, stream flow) this represents the rate of flow, the volume of flow and depth of flow of a watershed. |
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Term
| Explain quick flow vs base flow. |
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Definition
| - Quick flow or storm flow is based on rain events these peaks lead to floods while base flow has no immediate trigger. |
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Term
| Explain the stream flow generation processes. |
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Definition
- Direct precipitation, this is water falling strait into a water channel which makes up a very small percent.
- Overland flow, this is water moving over a surface. Infiltration will occur if the precipitation rate exceeds the infiltration capacity.
- Through flow, is the movement of water beneath the surface through the soil. Darcy law during rainfall events.
- Ground water discharge, this is the saturated zone under the ground. |
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Term
| Explain infiltration excess in humid temperate environments. |
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Definition
- Horton theory is another viable option when measuring ground infiltration rates or volumes. It is an empirical formula that says that infiltration starts at a constant rate, , and is decreasing exponentially with time, . After some time when the soil saturation level reaches a certain value, the rate of infiltration will level off to the rate .
- Organic material promotes infiltration and deep soils make high capacity. |
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Term
| What is partial area theory? |
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Definition
- This is where only some of the watershed is contributing. It is sustained by sub-surface flow.
- The zone next to rivers are close to saturation or at saturation. |
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Term
| What is variable source area theory? |
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Definition
| - Channels after rainfall shorten in distance and make the channel move faster. |
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Term
| What is antecedent moisture conditions? |
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Definition
- These are conditions before a rainfall event. In dry conditions the channels must fill and in wet conditions the channels already full.
- This is critical to generation of floods.
- Describes the relative wetness or dryness of a watershed. Antecedent moisture conditions change continuously and can have a very significant effect on the flow responses in these systems during wet weather. |
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Term
| Tropical environmental conditions for infiltration. |
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Definition
- These environments have thin soil which gives water no place to go.
- Soil saturates quickly after or during rainfall. |
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Term
| Semi-arid environments infiltration |
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Definition
- Rainfall is seasonal, the antecedent conditions before the season is very dry
- The soil is not very thick and saturates quickly causing overland flow.
- Infiltration capacity – the thin soil causes saturation and fast infiltration capacity during rainy season. |
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Term
| Infiltration of arid environments. |
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Definition
- Rainfall – monsoon season produce thunderstorms with dramatic rainfall events.
- Soil – very thin soil with low organic material. Horton flow model.
- Re-infiltration of overland flow – flash floods from high above infiltrates back into the ground downhill, this is critical. |
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Term
| Cold environments infiltration. |
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Definition
- Snowmelt accumulates and gets stored. It takes energy to melt the snow and a rain storm on snow can cause flooding.
- Frozen Grounds will have no infiltration so water flows across it. The permafrost is an area of ground that is permanently frozen.
- Organic soils, the material decomposes slowly due to the cold conditions and conductivity is very high. Named o-horizon allows for rapid sub-surface flow.
- Glaciers, have melt water coming out of the glacier caused by pressure melting the ice at the bottom as the temperature increases. Flash floods are caused by blockages. |
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