> Inlets in ICM InfoWorks and the Impact of Base Flow
The flow into a curb opening inlet is determined by multiplying the efficiency of the inlet by the upstream (u/s) flow in the channel connected to it. This means that the inlet captures a portion of the water flowing in the channel based on its efficiency. After a storm event has passed, and there is no longer any inflow into the channel, the inlet consequently stops receiving water.
Initially, the depth at the overland node, which represents the ground level at the inlet, is set to the ground level. This is because the simulation (SIM) uses the invert level of the control structure to represent the inlet's ground level. However, after the storm passes, the overland level is observed to be higher than the initial ground level, specifically ground level plus the base flow depth in the outgoing (d/s) channel, which is 0.02 meters in this context. This elevation is due to the requirement for the node to fill up to this new level before it can facilitate a continuation of flow in the downstream channel.
The presence of this non-zero depth in the overland node after the storm accounts for the observed spread in the overland flow. The spread is essentially the water that remains over the ground level due to the base flow in the channel.
One potential solution to drain the overland node and potentially reduce the spread back to zero is to apply the orifice equation, assuming there's still a non-zero depth remaining. This approach could more effectively model the draining process of the overland node by simulating the flow through an orifice, which is a more precise way to handle residual water.
It's important to note, however, that any reported spread may not fully capture realistic conditions due to the simplified assumption of constant base flow. The presence of base flow suggests there's always a minimal level of water in the channel, which may not be accurately reflected in the spread calculation without considering variations in base flow or the specific dynamics of water receding post-storm.
