Lynker Technologies Excel CRAM Water Resources Modeling Tool Excel CRAM is a powerful and flexible simulation framework for water resources systems that has modest personnel, hardware and licensing requirements. Excel CRAM provides high-level constructs for real-world system components such as inflows, river reaches, water demands and water rights, and reservoirs, that can be assembled into network representation of a real water resources system. This representation can then be used to simulate a time series of system operations and conditions based on a given set of inflows, water demands, and operating parameters. Excel CRAM is embedded in Microsoft Excel ® as an Add-In, so you can develop and maintain water resources system models in a familiar and low-cost environment. Both input pre-processing and output post-processing, including graphics, can be done using any of Excel’s native capability. This familiar environment and the flexibility it provides, along with Excel CRAM’s high-level interface means that minimal training is required before your personnel can develop, run and maintain an Excel CRAM model.

Developing an Excel CRAM model begins by creating network representation of a real system on the network palette. During this process the parameters for network components can be entered (e.g. reservoir capacity, water rights capacity and demand), or these can be entered later. (Any input data or parameters can be made a function of other values using Excel formulas.) Because of its very flexible and tolerant architecture, Excel CRAM lends itself to

experimentation and incremental model development. For example, splitting a river reach into two and adding a water demand can be accomplished with a few mouse operations and keystrokes—Excel CRAM takes care of re-organizing the data structures and provides you with a pre-defined worksheet into which any necessary time series data may be entered. Often, all that is required to simulate operations is to set priorities on flows in the network. If more control is desired, each time step can be broken down into two or more operating steps, wherein individual links can be manipulated and the network resolved. If even more control is required, VBA code can be written to simulate complex operational or physical behavior; well-documented program entry and exit points are provided at all stages of the network solution. Input to an Excel CRAM model can be linked to other Excel workbooks or Access databases. Output from an Excel CRAM model can be linked to other Excel Workbooks and Excel CRAM can automatically write input, output and network parameters to a Microsoft Access® database, including an ArcMap Personal Geodatabase.

Excel CRAM has been applied to a wide range of water resources problems at scales ranging from a mine-site water balance to the entire Colorado River Basin. The development and refinement of a model of the City of Boulder’s raw water supply system illustrates the power and flexibility of Excel CRAM. Boulder serves about 113,000 people using supplies from three different watersheds.

In the early 1980’s CRAM was used to develop a small network model of Boulder’s raw water storage and transmission system (this work pre-dated the development of the Excel add-in but used the same underlying simulation code). This model relied on historical time series of water rights yields that had been calculated by Boulder’s previous consultants. The City then asked us to develop a model of Boulder’s water rights, which required simulating all competing water rights in the Boulder Creek basin; the two separate models were maintained for several years. The last phase of model development involved integrating the separate water rights and system models

into a single network model. This integrated model proved its value when the City simulated the impact of projected climate change on its water supplied. The development of a model for Aurora Water also demonstrates how Excel CRAM provides the flexibility to proceed with model development incrementally without sacrificing simulation capability. Aurora serves a population of 310,000 people through a large and complex water collection and transmission system that obtains water from five different source areas. Aurora originally retained us to develop a model of the raw water system in two source areas. Later, Aurora asked us to incorporate models of the additional raw water systems into one integrated raw water system simulation. This Excel CRAM model has 79 time-series inflows, some of which represent consolidated water rights yields. The model simulated several complex water rights exchanges on which much of Aurora’s water supply depends. The Boulder and Aurora models are used by the utilities staff as part of routine planning and operations. Lynker Technologies supplements utility staff with our specialized expertise to assist with maintenance and refinement of the models.