1, this sentence means to draw the silt in Hanoi as far as possible to accommodate more river water. When the flying sand weir is built, the top of the weir should be low to facilitate flood discharge and sediment discharge.

2. "Deep scouring beach, low weir" is the famous saying of Dujiangyan water conservancy project. The "beach" in "Deep Taotan" refers to a section of Neijiang under Fengqiwo. After the flood every year, there will be sand and gravel siltation here, and it should be repaired frequently every year.

3. "Deep scouring the beach" means that the riverbed should be washed to a certain depth every year during the annual repair, and the water intake at the bottle mouth is too large, which will cause waterlogging; The scouring is too shallow, and the water in the bottle mouth is insufficient, so it is difficult to ensure irrigation. To this end, it is said that Li Bingcai buried stone horses under the river bed, and changed to bury iron in the Ming Dynasty as a sign of deep scouring.

4. "Low-level weir" means that when building a flying sand weir, the top of the weir should be low, which is convenient for flood discharge and sediment discharge, and plays the role of "diverting water to irrigate fields, diverting floods and reducing disasters".