1.   Purpose and objectives

     HYRROM is a conceptual rainfall runoff model developed for use on IBM compatible personal computers. The program has been designed to be easy to use, with no requirements to understand the computer operating system or the structure of the data files. Output is in the form of colour screen
graphics which can be copied to a plotter or graphics printer if required.

2.   Description

     The main use of a rainfall runoff model is to estimate river flows from rainfall and evaporation data. In HYRROM, flows are estimated using a simple, but realistic, representation of the physical processes which govern flows in a catchment.

     The HYRROM model uses the concept of "stores" to keep account of the passage of water through a catchment. These stores can fill or empty during a simulation, and provide a contribution to runoff which varies with the volume of water they contain. Four stores are used:  a surface routing store, an interception store, a soil store and a groundwater store. The user has access to 9 of the parameters which define the timing and magnitude of the flow from these stores. By varying these parameters, the
model can be calibrated to obtain a best fit between observed and estimated flows in the catchment. This optimization can be done manually, by the user, or automatically, using a built-in automatic optimization procedure (the Rosenbrock method). Once calibrated the model can then be used to
estimate flows for periods in which flow data are either unavailable or are of doubtful accuracy.

     Some typical applications of the model are: infilling missing flow data, quality control of data, extending historical flow records, generating synthetic flow sequences, water resources assessment.

3.   Input

     For calibration, the model requires a sequence of catchment average rainfall and river flow records. Either daily or monthly records can be used. Evaporation data must also be provided, preferably on a daily or monthly basis. However, if these are not available, annual data, or synthesized values, may also be used.

     The data must be contained in an ASCII (i.e. normal text) data file. A data preparation program is provided to assist with preparing this input data file. For users of the Institute's HYDATA database system (HOMS Component no.  G06.3.02), an option is provided to abstract the required data directly from the database.

4.   Output

     Screen graphics provide the main form of output. Hard copies of graphs can be produced on pen plotters, graphics printers or laser printers. Graph formats can be re-designed by the user. All results are also written automatically to ASCII data files for easy transfer to other software.

     Text and screen graphics will operate in monochrome or colour.

5.   Operational requirements and restrictions

     HYRROM is guaranteed to run on the following system: IBM AT, PS/2 or compatible (minimum 640k memory), high resolution graphics monitor, IBM/Epson graphic printer, HPGL compatible plotter (6 pens). A hard disk with at least 2 Mb free space is required.

6.   Form of presentation

     HYRROM is supplied on a number of IBM compatible 1.44 Mb diskettes. The software is accompanied by a comprehensive user manual in English.

7.   Operational experience

     The model has been used successfully on a wide range of hydrological studies, both in the United Kingdom and abroad.

8.   Originator and technical support

     The Institute of Hydrology, Wallingford.

9.   Availability

     From the HOMS National Reference Centre for the United Kingdom.

10.  Conditions on use

     As given in the agreement of sale. A charge is made for the software.