I've been busy modelling the urban drainage systems of various urban areas lately. The goal of these modelling studies is (generally) to identify where possible flooding of houses etc can occur during heavy rainfall events due to a lack of capacity of the drainage system. Im doing this using IW ICM, using 1D2D models.

Generally, my model is comprised of the drainage system, with all nodes set to 2D flooding, and all outlets set to 2D outlets. My 2D model is built up using LIDAR data, and for my mesh I utilise voids (buildings), mesh zones (for the dense urban area), and mesh level zones for the large waterways.

My question pertains to the modelling of the canals, big and small;
right now I use mesh level zones to burn the water level in the canals into the mesh. This way, i am only modelling the storage capacity of the canals. For small ditches, I use the LIDAR data. For the purpose of my calculations, this generally serves me well. However, problems arise at locations where I try to couple ditches together using 1D pipes (under roads and such). This either doesn't work (I read that this may be due to the mesh element size), or there are too many timestep halvings and the calculation fails.

My question to you is; how do you model urban waters such as canals and ditches in a combined 1D2D model, and specifically the connection between the 1D and 2D components? There must be a more elegant way than what I do now. I've read up on river reaches and inline banks a bit, but I'm not sure I should invest the time to master those options. Below is an example; red shows the ditch, blue is the pipe connecting the two ditches. In blue the water on the mesh is shown. The left ditch is full, yet the right one is not receiving water.
1d2d connection.PNG

Thanks in advance,