1.   Purpose and objectives

     ULTRA is a simple, user-friendly hydrological model for simulation of urban and rural watersheds. It can be used to generate design hydrographs from user-supplied input data on basin characteristics, design rainfall, and special computational control parameters. The model can also be used to calculate an approximate storage volume required to control the design hydrograph to a pre-determined release rate.

2.   Description

     ULTRA has two rainfall-runoff sub-models: NASHYD for rural basins and STANDHYD for urban basins. Both are lumped conceptual models having simple and limited input requirements.

     NASHYD has two main components - unit hydrograph and rainfall losses.The first is based on a cascade of identical linear reservoirs as was proposed by Professor Nash. Two parameters define the shape of the unit hydrograph. Rainfall losses are computed by means of the classical US Soil
Conservation Service (SCS) equation, where the storage in the soil is related to a curve number, CN. The CN is a function of land use, soil type and antecedent moisture conditions. The final hydrograph is obtained by convolution of the unit hydrograph and the rainfall excess.

     STANDHYD also has two components - unit hydrograph and loss function. The unit hydrograph is quasilinear and is similar in shape to a two parallel reservoir conceptual model. This allows a separate simulation of runoff from pervious and impervious areas. The storage coefficient for each reservoir is derived using kinematic wave theory. Losses are estimated for pervious areas from Horton's equation or from an SCS option. The hydrograph from each area is obtained by convolution. The two are then added together to obtain the final runoff hydrograph.

     Both sub-models have been extensively tested against measurements and compared with other, more sophisticated models. ULTRA has a calibration mode to assist in parameter selection. The design mode allows fast simulation of urban and rural design hydrographs for the selected parameters.

3.   Input

     Input depends on the selected sub-model. NASHYD requires two parameters to define the shape of the unit hydrograph, along with the event's initial abstraction and curve number. STANDYHD requires the slope, length, surface roughness, depression storage and the impervious area of the basin. Default values for these parameters are available. Both also require the drainage area.

     Storms as well as the resulting runoff hydrographs can be stored in order to assess the model parameters. Storms are stored and are used as input to create hydrographs.

4.   Output

     The resultant hydrograph can be stored for future reference. Tabular and graphical displays of the hydrograph and hyetograph are available. Simulated and observed hydrographs can be displayed together for  calibration purposes.

5.   Operational requirements and restrictions

     The ULTRA model operates on an IBM or compatible personal computer with only 64K of memory. A graphics monitor and a printer facilitate calibration. The model is written in BASIC and is compiled.

6.   Form of presentation

     Program and documentation in English on a 5.25 inch diskette.

7.   Operational experience

     ULTRA's sub-models are based on algorithms developed in the PC Interhymo (Otthymo 89) model. The Otthymo 89 model has been applied with success throughout Canada as well as in basins in Switzerland, Italy, Spain, Portugal, Cameroon, and the United States of America. It has been applied by over 50 Canadian organizations and is a recommended model in several Canadian guidelines for flood control and storm water management.

8.   Originator and technical support

     The ULTRA model was developed by J.F. Sabourin at Paul Wisner and Associates Inc., based on concepts developed by Dr. Paul Wisner and Messrs. J. P'Ng, A. Lam, and D. Jobin at the University of Ottawa. The originators will provide technical support.

9.   Availability

     From the HOMS National Reference Centre for Canada.

10.  Conditions on use

     The ULTRA model is available free-of-charge.