The model you see here is an example of IWRM because it combines several components: hydrology, a system network, operating rules, water rights law, and water demand forecasting. Let's take a look at how I've modeled each of these.
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| Screen Capture of the IWRM Example Model |
Note: As you read through this post, you'll see references to many example models in our library and links to our Help Documentation. These resources are designed to help you build and customize your own model.
Hydrology
The hydrology Container is the engine that drives the entire system. Instead of using a static time series of historical data, this model leverages various stochastic climate driver models that are available in our library. Let's start with a Markov chain precipitation model and a stochastic temperature and wind model. From these, we simulate air humidity and solar radiation, which are then used to calculate other weather-driven processes like snow pack, snow melt, and reference evapotranspiration, based on the FAO Irrigation and Drainage Paper 56 method. The entire system is driven by these stochastic inputs, which are based on historical data.
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| Screen Capture of the Hydrology Model |
You can tune these stochastic weather models before running your IWRM forecast simulations. Our website offers tools like "PrecipGen PAR," "TempGen PAR," and "WGEN PAR" that you can use to configure the models for your specific location.
Using the stochastic weather drivers, we can then calculate probabilistic watershed runoff for both the larger off-stream river and the local runoff that flows into our modeled system.
For more details on GoldSim best practices when modeling Watershed Runoff, refer to Runoff Modeling in GoldSim – GoldSim Help Center.
The System Network
The system network connects the water sources to the demands. The system I decided to model represents a regional water supply system that diverts river water to a offstream reservoir. It provides water supply for:
- Irrigation for agriculture
- Municipal supply for a city
- Environmental/recreational use
The river diversion controls the flow of water from the river to the off-stream reservoir. I used a Controller element to manage this diversion flow while continuously monitoring the status of the reservoir. A built-in check ensures the diversion rate is limited to the actual amount of water available in the river, which we calculate in the hydrology section.
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| Screen Capture of the System Model |
Diverted water flows from the river into the Pool of the reservoir model. The Pool element is a basic "GoldSim element" built into the software. I've added more functionality around this to account for inflows and control the outflows and monitor the current water level against various operational thresholds.
The reservoir must supply water for agricultural and municipal water use. Agricultural demand is simulated using crop scheduling based on crop areas and types, also drawing from the FAO Irrigation and Drainage Paper 56. Municipal demand is modeled using a forecasted population. For this, we use GoldSim's History Generator element, configured with a stochastic geometric growth function that considers mean annual growth rate, volatility, and a reversion rate. This IWRM model is sensitive to population, so for more detailed analysis, you could swap this out for a more complex cohort model. Municipal demand is further broken down into indoor and outdoor components of residential water use, modeling landscaping irrigation and indoor residential use.
We could easily add other factors to this model, such as water conservation practices or financial factors, by linking to other examples from our GoldSim library.
Reservoir Operations
The most complex component is the Reservoir Operations Model, which accounts for a variety of dynamic processes. Evaporation and precipitation are calculated using the hydrology functions we discussed earlier.
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| Screen Capture of the Reservoir Model |
For outflows, the model simulates both flood control and controlled releases. Flood and spillway flows are calculated dynamically; spillway flow is based on weir flow, while flood discharge is based on the hydraulic capacity of the outlet, which changes with the total head and friction losses. The outlet works are further controlled to supply water for downstream uses: municipal, agricultural, and environmental. A Controller element in the model continuously throttles the discharge to maintain a dynamic target water level in the reservoir. This discharge is also limited by the hydraulic flow capacity of the outlet. This creates a feedback loop, as they monitor the reservoir status before water is supplied for municipal and agricultural demands. All of these components are conceptually modeled in the example.
The Allocator element simulates the application of water rights. In this model, we have set the water rights to prioritize irrigation, so municipal demand must acquire additional supplies from groundwater wells when the reservoir cannot meet their needs. This often happens in summer during peak demand and continues into the fall when they are trying to refill the reservoir. The water rights logic is built into this model using basic GoldSim elements.
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| Screen Capture of the IWRM Model, with Probabilistic Results |
The beauty of this model is that all the uncertain inputs propagate through every component to produce probabilistic time history outputs. This allows us to visualize a range of possible operational scenarios, giving us a powerful tool for risk-informed decision-making.To download a copy of this model, visit the page in our library: Modeling Integrated Water Resources Management (IWRM) with GoldSim – GoldSim Help Center
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