Weirs are hydraulic structures which act as a barrier across the direction of flow for the purposes of measuring flow, increase upstream water head, flow diversion, protect river banks, reduce erosive energy and allow for fish passage, grade control, river rehabilitation and restoration etc. The shapes vary from rectangular horizontal weirs over V-notch, oblique, ogee, curved, labyrinth & piano key weirs to alphabet weirs.

In-stream rock weirs of alphabet shape (U, A and W shape) are now being famous because of their interesting shapes and functionality. The traditional concrete structures are expensive, resulting in poor fish habitat and less naturally accepted which lead to the development of U-, A- and W-weir. Alphabet weirs can be used to establish grade control, reduce stream bank erosion, energy dissipation, increase aquatic habitat etc.

The in-stream rock weirs of alphabet shape are not a very old concept and the design and guidelines of these structures are not based on the physical process. More experimental study is required and qualitative field investigation should incorporate with numerical model with wide range of scenario to better understand the physics for proper design of alphabet weirs.

Accuracy of MIKE 11 to calculate upstream flow depth in rectangular channel is evaluated by incorporating broad-crested weir and alphabet weirs. These simulations were performed only for free flow condition. Laboratory experiments data used to model these weirs. The analytical outcomes following the weir equations derived for broad-crested weirs and alphabet weirs are compared with results obtained with MIKE 11 using the Broad Crested Weir option as well as Weir Formula 2. For both the weirs, MIKE 11 gives good agreement while comparing with analytical results and the observed data.