Concept:
A Parshall flume is a flow measuring structure used in open channels.
Step 1: In irrigation channels, water may contain silt and floating debris.
Step 2: Devices like small orifices may get clogged when debris or silt is present.
Step 3: A Parshall flume has an open throat and allows water to pass smoothly.
Step 4: Because of its design, it is less likely to get clogged by suspended silt or floating materials.
Step 5: Therefore, the correct answer is Parshall flume.
\[
\boxed{\text{Parshall flume}}
\]