To study the hyporheic exchange driven by a single peak flood-induced water level fluctuation (i.e. flood wave), a method combining numerical simulation with theoretical derivation was proposed based on the Inbuk Stream, Korea, where flooding occurs frequently. The hyporheic exchanges induced by different flood waves were investigated by varying amplitude (A), duration (T), wave type parameter (r), and rising duration (tp), which were adopted from the real-time stream stage fluctuations. Additionally, the idea of constant upstream flood volume (CUFV) condition for flood waves was put forward, and the effects of “Botan” (T/A) and peak number (N) on hyporheic exchange were studied. The results showed that the hyporheic exchange flux (q) was controlled by the water level h (sine-type) and its change rate v (cosine-type), and was proportional to the polynomial of them q“∝” (ω∙h+v), where ω is the angular frequency of the flood wave. Based on this mechanism, the influence principles on hyporheic exchanges of the typical flood wave parameters (A, T, r and tp) as well as T/A and N under CUFV condition were clarified. The main characteristic variables of hyporheic exchange, which were maximum aquifer storage and residence time, were positively correlated. They also had positive relations to the integral of the flood wave over time, which increased when the wave became higher, wider, rounder and less skewed. However, when CUFV condition was imposed, the residence time was positively correlated with T/A, whereas the maximum aquifer storage was negatively correlated with T/A. With the increase in N, water exchanged more frequently and some water returned to the stream early, leading to the slight decrease in maximum aquifer storage and residence time. These findings enriched the theory of hyporheic exchange driven by surface water fluctuation and be of great significance to enhance pollutant degradation in the hyporheic zone downstream of reservoirs.

Managing reproduction is the most effective approach to sustain population or control invasion of species. Flow velocity is recognized to affect the reproduction of fishes spawning drifting eggs in rivers. Despite plenty of studies on this aspect, quantitative relations between flow velocity and fish reproduction, including spawning, fertilizing, hatching and surviving, has not yet been established. Here we for the first time quantified the relationship between flow velocity and reproduction of Chinese carps through lab experiments as well as field surveys. The results showed that a minimum velocity was required to trigger Hypophthalmichthys molitrix (H. molitrix) releasing eggs, and a velocity range was preferential to sustain spawning activity. However, the embryo incubation and larvae development of H. molitrix were found to be inhibited with the increase in flow velocity. Considering the requirements of spawning and hatching as well as larvae development, a compromised optimal flow velocity was identified for reproduction of H. molitrix in rivers. The findings were of great significance to guide the operation of cascade dams to create suitable flow velocities during reproduction season for either improving population or impeding invasion of carps.

Set in the downstream riparian zone of Xin’an River Dam, this paper established a two-dimensional coupling flow and solute transport and reaction model, and explored the denitriding methods and principles in the riparian zone from the perspective of hyporheic exchange, which provided a basis for the engineering techniques for river ecological restoration. Our studies have shown that under the condition of water level fluctuation, biological method such as adding denitrifying bacteria biomass could greatly increase the denitriding rate in the riparian zone; chemical methods such as adding organic carbon into the surface water or groundwater could increase the total riparian nitrogen removal and its efficiency to a certain extent; hydrogeological methods such as silt cleaning of the aquifer surface or local pumping around the contaminated area could increase the total riparian nitrogen removal to some extent, but correspondingly reduce the denitriding efficiency; physical methods such as designing the bank form into gentle slope or concave shape could slightly increase the total riparian nitrogen removal and correspondingly improve the denitriding efficiency. At the application level of river ecological restoration, integratedly adopting the above methods can make the riparian denitriding effect “fast and good”.