Multiple Catchment Runoff


Illustration of Calculation Abstraction Methods Available in GoldSim


This model calculates runoff from three catchments during a year. The same equation is used to calculate runoff for each catchment. However, the input parameter values for each catchment are different because these parameter values are related to the physical characteristics of the individual catchments. The purpose of the model is to demonstrate different methods of abstraction which are built into GoldSim.

Abstraction in this case refers to completing an identical calculation three times with different input values. The function/equation is then constant for all three catchments but the inputs to the calculation are different for each catchment. The calculation for each catchment then represents an instance of the general catchment runoff calculation.

Three different abstraction methods are employed to complete the runoff calculation for the individual catchments. Each abstraction method is represented in a separate container. These abstraction methods are:

  1. Localized Containers: see "Localized_Containers";
  2. Cloned_Containers: see "Cloned_Containers"; and,
  3. Array Functions: see "Array_Functions".

The purpose of this model is to demonstrate abstraction techniques in GoldSim. A specific calculation (runoff from a catchment) is used as an example. To facilitate the interpretation of this model as a general abstraction example, additional details of the specific calculation used are provided in the following.

A catchment is the land area over which precipitation (rain) falls. Runoff is the portion of the rain which falls on the catchment surface that flows over the land surface. A watershed is the land area, or catchment, which contributes surface runoff to a point of interest (i.e. the watershed outlet point or point of concentration.

In this model, the discharge from each watershed is calculated from daily rainfall using the Rational method. Basic discharge statistics are also calculated for each year. The Rational method relates peak discharge (Q) to a runoff coefficient (C), rainfall intensity (i), and watershed area (A).

Q = C * i * A

The same rainfall intensity is used for each catchment, but the values of C and A vary by catchment. The model runs 67 realizations or 67 different 1 year simulations. For each simulation, the year is incremented so that each simulation runs a different year of the input precipitation data set. The precipitation data set and precipitation value calculations are contained in the "Model_Data" container. Each abstraction method container holds a "Results" container which provides results for each method to facilitate comparison of the methods.


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