FAQ / Reasons for setting the HQ formula application lower flow limit and the HQ formula application upper flow rate¶
When should the HQ expression [HQ 式適用下限流量] and [HQ type applied upper flow limit] be used?
If a cross section of a river is limited to a certain range of flow rates to which the HQ formula should be applied, [HQ 式適用下限流量] set and [HQ type applied upper flow limit] .
In addition, the manual for creating a flood prediction area map (4th edition) July 27, p. 9 states as follows.
Manual for Drawing Flood Expected Areas (4th Edition) July 27 Reference 3 Guidance for Inundation Analysis in the Event of Flooding Exceeding the Plan Scale (Draft) p. 9
According to the hydraulic analysis method and hydraulic conditions used in the river channel plan, the water level of each cross section for each flow rate scale in the current river channel is calculated, and an H-Q formula such as Q = a (H + b) 2 format is created. River channel water levels may be overestimated. Therefore, when calculating the flow rate equivalent to the height of the levee, it is necessary to pay attention to the upper limit of the overflow water depth, and to use the irregular flow calculated water level that takes flooding into account instead of the converted water level according to the H-Q formula consistent with the river channel plan.