Concept:
A weir is a hydraulic structure used to measure discharge in open channels.
Step 1: Different types of weirs are used for different flow ranges.
Step 2: V-notch weirs are generally suitable for small discharges because they are sensitive at low flows.
Step 3: Cipolletti weir is a trapezoidal weir.
Step 4: It is commonly used for measuring medium discharges.
Step 5: Therefore, the correct answer is Cipolletti weir.
\[
\boxed{\text{Cipolletti weir}}
\]