RHYHABSIM

RHYHABSIM was developed to provide hydrologists, engineers and resource managers with an integrated solution to some of the more common hydrometric and hydraulic computations in flow assessment, such as:

• calculation of flow

• stage/discharge rating curves

• water surface profile analysis

• incremental flow analysis (IFIM), including flushing flows, sediment deposition, and flow fluctuations

• water temperature modelling

The basic stream geometrical unit is a cross-section. A reach of river is a number of cross-sections that represents either a length of the reach or a percentage of the reach. This forms a model of the stream reach. A reach is usually a section of river with similar morphology (i.e., slope, geology, channel form, and flow). Braided or multi-channel sections of a river can also be modelled.

Reaches can be combined to give a total along a longer section of river.

Measurements of water level and flow at each cross-section are used to calibrate the model, which can then be used to predict water level, velocity and habitat suitability over a range of flows. Any combination of reaches and cross-sections can be combined

to predict water level, velocity and habitat suitability over a range of flows. Any combination of reaches and cross-section can be combined for habitat analysis.

An automatic calibration procedure fits water levels and flows (rating calibration gaugings) to rating curves. For prediction of point velocities, the conveyance at each measurement point is related to the measured velocity. This ratio is the velocity distribution factor (VDF) and is used to calculate velocities at other flows.

Up to 10 instream characteristics or attributes can be described at each measurement point. Typically, an attribute describes substrate, instream cover or water surface character, but any attribute may be recorded.

Instream habitat suitability criteria or statistical models, such as Generalised Additive Models GAMS),can be applied to the simulated or measured water depths, velocities and recorded attributes to give the weighted usable area (WUA) of instream habitat.

RHYHABSIM has been superceded by SEFA (System for environmental flow analysis)

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