Hydrologic models / REF / 250 / 2014

Hydrologic models are simplified, conceptual representations of a part of the hydrologic cycle. They are primarily used for hydrologic prediction and for understanding hydrologic processes. Two major types of hydrologic models can be distinguished:

• Stochastic Models. These models are black box systems, based on data and using mathematical and statistical concepts to link a certain input (for instance rainfall) to the model output (for instance runoff). Commonly used techniques are regression, transfer functions, neural networks and system identification. These models are known as stochastic hydrology models.
• Process-Based Models. These models try to represent the physical processes observed in the real world. Typically, such models contain representations of surface runoff, subsurface flow, evapotranspiration, and channel flow, but they can be far more complicated. These models are known as deterministic hydrology models. Deterministic hydrology models can be subdivided into single-event models and continuous simulation models.

Recent research in hydrologic modelling tries to have a more global approach to the understanding of the behaviour of hydrologic systems to make better predictions and to face the major challenges in water resources management

Groundwater modelling

Groundwater models are computer models of groundwater flow systems, and are used by hydrogeologists. Groundwater models are employed to simulate and predict aquifer conditions.

Surface water modelling

Runoff model (empirical)

These models use an empirical method to convert rainfall volume into runoff volume. An example is the Curve Number method.
The runoff curve number (also called a curve number or simply CN) is an empirical parameter used in hydrology for predicting direct runoff or infiltration from rainfall excess. It can be used with a unit hydrograph to derive the runoff rate from the direct runoff by convolution.

Runoff model (reservoir)

These models describe rainfall-runoff relations using the concept of a (non)linear reservoir. Examples include: Vflo.

Hydrological transport model

These models describe the flow and routing of water once it has entered a river/stream system and the transport of dissolved or suspended material and debris in a river/stream. Examples include MIKE 11, MOHID, WAFLEX and DSSAM.

Composite models

Many models combine two of these types, for example HBV, which is combines an empirical runoff model and a hydrological transport model. Some models combine elements of surface water models and groundwater models, for example GSSHA, MIKE SHE, and WEAP.

Agricultural hydro-salinity modelling

Agricultural hydro-salinity models like SaltMod, Swatre  and Drainmod  are models integrating hydrological factors like irrigation, evapotranspiration and groundwater flow to simulate the behavior of the water table and soil salinization and to assess agricultural engineering measures like watertable control and soil salinity control by subsurface drains, drainage by wells and salt leaching.
SahysMod  is a polygonal combination of SaltMod with a groundwater model.


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