Hydrologie II, part II
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zweiter teil
Fichier Détails
| Cartes-fiches | 96 |
|---|---|
| Langue | English |
| Catégorie | Géographie |
| Niveau | École primaire |
| Crée / Actualisé | 29.12.2013 / 16.01.2017 |
| Lien de web |
https://card2brain.ch/box/hydrologie_ii_part_ii
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variable source areas
extend and contract according to the wetness state of the catchment.
basis of many conceptual models.
typically only a small part is fully saturated and creates saturation excess runoff
2 reasons for preferential flow paths
macropores: due to biological activity, roots, animals. usually close to the surface
fingering flows: unstable wetting fronts due to persistent flow patterns created by soil heterogenity
where does subsurface flow occure?
i) close to surface, between organic and mineral soil
ii) deeper, at interface between bedrock and soil
which simple methods for generating runoff in large areas exist?
equivalent infiltration capacity infiltration excess runoff
bucket model, saturation excess runoff
equivalent infiltration capacity + initial abstraction
φ method
whats the equivalent infiltration capacity model?
assumes infiltration excess runoff
for long-term events and large catchments
R = P-K^
whats the bucket model?
based on saturation excess runoff
for relatively wet catchments and topographic controlled streamflows
Smax = Zsoil*(θsat-θr)
whats the equivalent inflitration capacity + initial abstraction method?
its a combination of equivalent infiltration cap and bucket model.
first saturation excess is used (bucket), then infiltration excess
R = (P-Ia)-K^
what is the φ method?
a percentage of rainfall is used to generate runoff
for short events and small catchment areas,used for design small hydraulic structures
R=φ*P
3 conceptual models based on saturation excess mechanism
topmodel
vic model
pdm model
how does the topmodel work?
overland flow occurs when the water table crosses the topographic surface thus determining a saturated area which contributes to the overland flow. its a topographically controlled model.
when is the topmodel used?
when topography is very distinctive or no data is available (except a DEM)
hypothesis of topmodel
there is a saturated zone in equilibrium with a steady state recharge rate over an upslope contributing area "a". qi = P*ai
water table is parallel to the surface auch that the effective hydraulic gradiant is equal to the slope of the local surface qo=T(zi)*tan(ßi)
only gravity, no capillarity
stationary conditions qo=qi
hydraulic conductivity decreases exp with depth
depth of bedrock Z is much larger than depth of water table zi
VIC model
variable infiltration capacity model
runoff Q = Rainfall - added storage DS
added storage is calculated based on the initial storage at wt
Summary of the tools for building a rainfall runoff model
.
physical mechanisms of rainfall runoff processes
non linear
time varying
distributed in space
characterized by heterogenities, anisotropies....
"randomly" varying in time and space
assumptions rainfall runoff transformations
linearity: I1(t)*e -> o1(t)*e, I1+I2->o1+o2
time invariance: I1(t)->o1,I2(t+tau)->o2
lumped description
-> linear model, conceptual and lumped describtion of basin response
