Initialization of Crop Areas

The IAMDD simulation engine utilizes an advanced, agronomically accurate soil water balance (SWB) model to manage the automated irrigation scheduling for agricultural areas. This document details how crop areas are initialized at Simulation Time 0 (ETime 0) and the operational logic that governs automated headgate controls.

1. Agronomic Principles & Soil Water Bounds

To simulate realistic crop behavior, every agricultural area calculates its own unique soil water constraints based on its assigned Crop Type and Root Depth:

• Field Capacity (FC): The maximum amount of water the soil profile can hold against gravity. This represents a fully saturated, healthy root zone.
• Permanent Wilting Point (PWP): The soil moisture level at which plants can no longer extract water and will suffer irreversible damage.
• Total Available Water (TAW): The total volume of water held between Field Capacity and the Permanent Wilting Point (TAW = FC - PWP).
• Management Allowable Depletion (MAD): A crop-specific safety threshold representing the percentage of TAW that can be depleted before yield-damaging stress occurs (e.g., typically 50% for deep-rooted crops like Alfalfa).
• Readily Available Water (RAW): The actual volume of water the crop is allowed to consume before irrigation is required (RAW = TAW * MAD).

2. Initial State Distribution (The Snapshot Mechanic)

A realistic irrigation district does not begin with all fields entirely full, nor does it begin with all fields in a drought. At any given moment, the soil moisture of the various fields across the district is staggered.

To replicate a realistic "Snapshot in Time" at ETime 0, the IAMDD engine utilizes a randomized distribution to initialize each area's starting Soil Water Balance (swb):

• Healthy Bounds: The engine strictly confines the randomized starting moisture to the Readily Available Water (RAW) zone.
• Distribution: Soil moisture is randomly initialized between the MAD Limit (100% of RAW depleted) and Field Capacity (0% of RAW depleted).
• This ensures that no crop is artificially forced into a severe drought state merely to trigger water flow at the start of the simulation.
• The random initial state can be overridden by entering a user defined initial soil water depth in the area properties.

3. Active Irrigation Probabilities at ETime 0

In real-world operations, farmers do not wait until every field hits the exact MAD limit to start the pumps. At any given snapshot in time, several fields are already in the middle of active irrigation cycles.

To ensure realistic hydraulic flow at the very first timestep without relying on drought conditions, the initialization engine evaluates the randomly assigned starting soil moisture for each area:

• If an area's initialized swb is in the lower 40% of its RAW zone, the model determines that the farmer/system likely triggered the irrigation earlier in the day.
• The engine applies a 40% probability that this specific area is ALREADY_ON at ETime 0.
• This probabilistic approach guarantees a realistic initial demand on the canal or pipeline network, allowing the hydraulic solver to immediately calculate flows, pressures, and drawdowns right out of the gate.