3.2 Influences of typical flood wave parameters on HE
The q +max, |q |-max andQ max showed increasing trends with A (Fig. 5a1, a2); with each 50% increase in A ,Q max increased by about 0.354 m2. The increase of A signifies that at any time, the height of the water level and its change rate have increased, and thus q and Q increased correspondingly, based on formula (8). The change of RT was the same as that ofQ max. When A increased by 50%, RTincreased by about 2.21 days. The ratiot R/t F increased withA , mainly because t R increased withA , while t F changed only slightly (Fig. 5a2). In order to clearly show the variation of characteristic HE variables with the flood wave parameters, the main results are summarized in Table 2.
The q +max and |q |-maxdecreased with T , and their occurrence times were postponed accordingly (Fig. 5b1), while Q max increased withT and its occurrence time was postponed, too (Fig. 5b2).Q max increased by about 0.233 m2 when T increased by 50%. An increase inT signifies the water level rising or falling slowly, as a result, q +max and |q |-maxdecreased accordingly. The occurrence times ofq +max and |q |-max were postponed with increasing T , because of the delayed appearance of the wave peak. Q max increased with Tbecause a larger T indicates a longer period of stream water recharging the groundwater. RT was proportional toQ max, and the averaged increase in RT was 2.18 days for each 50% increase in T . However,t R/t F decreased withT , mainly because t R increased less thant F (Fig. 5b2).
The q +max increased withr and its occurrence time was postponed; on the contrary, |q |-maxdecreased with r and its occurrence time was early (Fig. 5c1). The behavior of Q max was the same as |q |-max (Fig. 5c2). The Q max decreased by about 0.128 m2 as r increased by 50%. When rincreases, the flood wave becomes “thin” (Fig. 2) and the overall water level decreases, which caused the maximum recharge of stream water to groundwater (Q max) to decrease accordingly. The thinner the flood wave, the larger the change rate of water level around the wave peak, and the smaller the change rate of water level around the initial value of the water level. Therefore, from formula (8), q +max and |q |-maxincreased and decreased with increasing r , respectively. Furthermore, the thinner the flood wave, the later the water level rises to a certain height, and the earlier the water level falls to a certain height. This phenomenon can better explain whyq +max and |q |-maxoccurred later and earlier, with the increase of r . In addition,RT decreased 1.01 days on average, for each 50% increase inr . However, t R/t Fincreased with r , mainly because t Rdecreased less than t F (Fig. 5c2).
The q +max, |q |-maxshowed decreasing and increasing trends with t p, respectively, and the occurrence times of both were postponed (Fig. 5d1). Q max increased witht p, and its occurrence time was also postponed (Fig. 5d2). Q max increased by 0.0933 m2 for each 50% increase int p. An increase of t p(i.e. wave crest is less skew) (Fig. 2) signified that the rate of water level change decreased during the rising limb and increased during the falling limb of the same water level, which resulted in the corresponding decrease and increase ofq +max and |q |-max, respectively. Similarly, with the increase of t p, the moment of the water level rising or falling to a certain height were delayed, which explained why the occurrence time ofq +max and |q |-max were postponed. In addition, Q max increased witht p, which was caused by the corresponding increase of the overall water level. For each 50% increase int p, the average increase in RT was 0.45 days. However, t R/t Fdecreased with t p as t Rincreased less than t F (Fig. 5d2).