The objective of this model is to estimate monthly water usage patterns and apply them to a projected, annual base demand to simulate future time-varying demands for a water system. The first step is to review historical data to determine current seasonal demand rates and then calculate normalized multipliers. Once the normalized multipliers are determined, they can be applied to projected base demand rates for your system model. This method assumes that the seasonal variations will not change over time.
System flows experience changes on a daily, monthly, and annual basis. For purposes of demonstration, this model will consider monthly changes in water demand. Monthly changes in demand can usually be traced back to climatic variables such as temperature, precipitation, agricultural practices, and to a lessor degree the changing habits of the water users such as recrational activities.
This model uses built-in array functions ("getrow" and "meanc") to return the demand of the current month of the simulation and then to calculate an annual average water demand over the 12 monthly values. This is done for an array of usage types including agricultural, municipal, and industrial. A normalized multiplier is calculated by dividing the average demand by the monthly demand. Now this multiplier can be applied to forecasted annual average demand scenarios. A lookup table contains future average usage rates from 2010 thru 2030.