Runoff analysis and prediction by the flood critical model

洪水発生限界モデルによる流出解析と予測

Runoff analysis and prediction by the flood critical model

Creators Shiotsuki Yoshiharu

A new simple method for runoff analysis and prediction will be introduced in this paper．We can express the basin water budget by Eq.(1) and the flood critical circumstance of river basin by Eq.(2), respectively, where all hydro-terms reach to the saturated with suffix c, like as, rainfall R→Rc mm/hr, river flow at basin inlet Q1→Q1c m3/s, river flow at basin outlet Q2→Q2c,indirect runoff Qw→Qwc, evaporation e→ec mm/hr, base flow Bf→Bfc mm/hr, storage change of basin water ΔW→ΔWc mm/hr, infiltration g→gc mm/hr． Here, alp is called the rainfall coefficient in this paper and is used to formulate the direct runoff from rainfall, alp×R． When we have much more R and Q1 in this critical state, the flooding flow Q2 can be expressed as Eq.(8) by subtracting Eq.(2) from Eq.(1)． As we can set Bfc≒Bf, ΔWc≒ΔW, gc ≒g and ec = e = 0 in the critical state, the river flood O and the inundation I can be written as Eq.(6) and (8), respectively． The new necessary river conveyance capacity Q2cN is written as Eq.(11) well to drain both of O and I, where (1-zet) ×I is the direct runoff and II is the indirect from accumulated inundation Is．Here, zet is called the stagnant coefficient．The flood critical state for us is mainly determined by the river conveyance capacity, while for other beings like fishes, birds, and aquatic animals must there each flood critical．Various different flood critical states will be defined for some beings even when the low river water stage．Therefore, it may be considered that the present flood critical model can be applied to any states of river flow and can be used to estimate new flow Q2cN．The results of runoff analysis show the present method to be useful for not only the analytical work but the predictive work in cases of river basin with small alp．

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