|
Water Resource Associates |
HYSIM Information Pack
INTRODUCTION
HYSIM is a powerful, modern, flexible rainfall/runoff modelling system. This information pack describes the model, what can be done with it and how it works. It has recently been chosen by the United Kingdom Environment Agency as their national standard rainfall/runoff model
What it is
HYSIM is a Hydrological Simulation Model which uses rainfall and potential evapotranspiration data to simulate river flow. Its parameters, for hydrology and hydraulics, define the river basin and channels in a realistic way. Whilst being realistic the model is easy to use. HYSIM has a long pedigreee and has been described in a number of publications.This has a number of advantages.
w Such a model is more likely to perform well in climatic conditions more extreme than those in its calibration period.
w As the model does not rely entirely on measured input and output data for its accuracy, but can also use data such a soil type and rooting depth, it can be used to study catchment changes.
w It enables good initial estimates to be obtained for model parameters.
The theory behind the hydrological and hydraulic aspects of the model is described in separate sections.
What data it needs
HYSIM is flexible in its data requirements. As a minimum it needs precipitation and PET data but it can also use data on snow melt, abstractions from and discharge to surface water and pumping from groundwater. The data can be daily or any shorter time step. The time step for different types of data and for calculations do not need to be the same.
Not only is HYSIM flexible in its data requirements, it is also flexible in terms of catchment definition. Within a single sub-catchment it is possible to represent channels by up to 20 reachs and to have three zones, each of which can have its own parameters and data, to represent hydrological or climatic heterogeneity. It is also possible to link a series of sub-catchments to simulate large complex river basins.
What it can do
River flow extension. Rainfall and other meteorological records are typically of longer duration than flow records. Using a few years of flow and meteorological data to calibrate the one can then simulate flow for a longer period.
Climate change. By simulating a river basin with different climate scenarios it is possible to assess the effects of climate change on river flow and groundwater levels.
Flow naturalisation. HYSIM can simulate a catchment as it is, with man-made influences such as groundwater abstraction or urbanisation. It can be calibrated using a flow record which reflects these influences. The flow extension can then be carried out with the parameters and data modified to remove these effects thus giving a naturalised flow record.
Groundwater/surface interaction. The fact that HYSIM can simulate groundwater pumping, its effects on groundwater storage and consequent effects on runoff, enables it to be used for conjunctive use studies.
How it does it
HYSIM’s strengths come in the following areas:
w Data entry and preparation, often a very time consuming part of a simulation project, are facilitated within HYSIM. Some of the features include rainfall data infilling, calculation of mean basin rainfall, comparison of flow and current meter gaugings and manipulation of data files.
w Parameter entry is done within the model with no need for editing of text files. On line help is available to aid in parameter selection.
w Graphics facilities include plotting of data, observed and simulated flows and double-mass plots. As well as on-screen plotting the graphs can be sent to a printer or to Windows Metafile format files.
w The model itself has a built-in optimisation algorithm which facilitates calibration.
Other uses
HYSIM has other more advanced facilities which include:
w Calibrating the model with daily data but studying major floods using hourly data. It is possible to output values of moisture storage on a daily basis and use these to restart the model on a particular day. One could then simulate a flood flow for a few days.
w Modelling of the soil layers in a realistic way. HYSIM is therefore able to simulate variations of moisture in the soil which could be used for studies of chemical leaching.
w Outputting intermediate values of calculations. This enables HYSIM to be used with other more specialised models. For example runoff could be used with a hydraulic model for detailed studies of flood alleviation measures or the percolation to groundwater could be used as input to a hydrogeological model.
Documentation
Two documents are provided with HYSIM. The User Guide describes how to set up data and parameters, calibrate the model and produce the results. The guide also contains an exercise covering most aspects of using HYSIM. The Reference Manual gives more details on the theory behind the model and the format of the data files.
Uses of HYSIM
HYSIM has been used in Europe, Africa, South America and Asia. Its uses have included:
w Flow record extension and infilling,
w Flow naturalisation,
w Conjunctive use of surface and groundwater,
w Flood studies, both independently and with hydraulic
models,
w Groundwater studies, both independently and with
hydrogeological models,
w Studying effects of climate change.
Computer requirements
HYSIM runs under Windows Vista/XP and earlier versions.
Additional information
Contact: Ron Manley
HYSIM Hydrology, HYSIM Hydraulics, Use of HYSIM, Papers on HYSIM