Reinforced concrete (RC) structures are commonly strengthened using externally bonded fiber-reinforced polymer (FRP) sheets. The bond between the FRP and concrete is a crucial factor affecting the strengthening effect, and debonding along the FRP–concrete interface is usually accompanied by the fracture of the underlying concrete. Therefore, it is necessary to identify the interface damage of FRP-to-concrete joints and conduct mechanical analysis. However, debonding is invisible damage that occurs inside the underlying FRP layer, which makes damage detection more difficult. To this end, this study fuses a percussion method with a deep learning framework to address the detection of such invisible lesions. Meanwhile, the visualization study provides guidance for later maintenance work. To further illustrate the hazard of the identified lesions, three-dimensional reconstruction for finite element modeling (FEM) with detected damage information based on percussion is proposed to elucidate the mechanical degradation caused by the fracture of underlying concrete. Lastly, the results of this study demonstrate that the detection, visualization, and FEM reconstruction of FRP–concrete interface damage using percussion signals has considerable application potential and is worthy of further study.

The interaction of groundwater (GW) and surface water (SW) not only sustains the runoff in dry seasons, but also plays an important role in regulating aquatic ecosystems. Hydrological engineers proposed the idea of modeling flood routing using the Muskingum-Cunge method, by ignoring GW-SW interaction during flooding which may however contribute to the outflow. This study proposes an improved nonlinear Muskingum-Cunge flood routing model considering lateral inflow, which is denoted as NMCL1 and NMCL2 that can simulate the flood routing and calculate GW-SW exchange. In addition, both the linear and nonlinear lateral inflow (with the channel inflow) are discussed, and both the stable lateral inflow due to GW-SW exchange and the transient/conventional lateral inflow changing with the river inflow are considered for the first time. Sensitivity analysis has shown that different parameters have different effects on the simulation results. Three different flood cases documented in literature with one measured from Zhongtian River, China, were selected to compare the classical and the updated Muskingum-Cunge methods. Two different floods of the River Wye are selected to verify the accuracy of the calibrated model. Comparison has shown that, for several cases, the proposed method is capable of obtaining the optimal simulation results. For the case of Zhongtian River, the proposed method can estimate the GW-SW interaction and lateral inflow reliably. The proposed method inherits the ability of Maskingum-Cunge in flood routing. Moreover, the new Muskingum-Cunge method can quantify GW-SW exchange, and the estimation has reliably owned to the nonlinearity and sign flexibility of the calculated exchange process.

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The interaction of groundwater (GW) and surface water (SW) not only sustains the runoff in dry seasons, but also plays an important role in regulating aquatic ecosystems. Hydrological engineers proposed the idea of modeling flood routing using the Muskingum-Cunge method. This study proposes an improved nonlinear Muskingum-Cunge flood routing model considering lateral inflow, which is denoted as NMCL1 and NMCL2 that can simulate the flood routing and calculate GW-SW exchange. In addition, both the linear and nonlinear lateral inflow (with the channel inflow) are discussed, and both the stable lateral inflow due to GW-SW exchange and the lateral inflow changing with the river inflow are considered for the first time. Sensitivity analysis has shown that different parameters have different effects on the simulation results. Three different flood cases documented in literature with one measured from Zhongtian River, China, were selected to compare the classical and the updated Muskingum-Cunge methods. Two different floods of the River Wye are selected to verify the accuracy of the calibrated model. Comparison has shown that, for several cases, the proposed method is capable of obtaining the optimal simulation results. The proposed method can estimate the GW-SW interaction and lateral inflow reliably, and inherits the ability of Maskingum-Cunge in flood routing. Moreover, the new Muskingum-Cunge method can quantify GW-SW exchange, and the estimation has reliably owned to the nonlinearity and sign flexibility of the calculated exchange process.

<p>Hyporheic exchange is transient in nature, considering the temporal fluctuations in hydrological and/or biogeochemical conditions in surface water and groundwater (SW/GW).  Efforts are needed to further identify the patterns and driving mechanisms of transient hyporheic exchange.  This study combined a reach-scale field survey and numerical modeling analysis to reveal the pattern of transient hyporheic exchange during rainfall events in the Zhongtian River, southeast of China. Field observations revealed hydrodynamic properties and temperature variations in SW/GW, suggesting that the regional groundwater recharged the study reach.  A one-dimensional heat transport solution was built and used to generate the planar and cross-sectional hyporheic flow fields. A two-step numerical modeling procedure, including a hydraulic surface flow model and a groundwater flow model, was then used to simulate the observed flow system. The hyporheic exchange exhibited strong temporal evolution, as indicated by the rainfall event-driven hyporheic exchange, the depth-dependent hysteretic response to rainfall, and the area of local downwelling flow increasing with rainfall. Dynamics of the hyporheic exchange in the study reach, therefore, significantly changed in space and time due to rainfall. The reversal of hydraulic gradient and transient hyporheic exchange were observed and validated using the numerical simulation. Anisotropic hydraulic conductivity is the key to generate transient hyporheic exchange. A revised conceptual model was used to interpret the observed temporal patterns in hyporheic exchange  The pattern of transient hyporheic exchange indicates that transient hyporheic exchange only appears after an increased phase of river stage but does not last for a long time. The temporal pattern of hyporheic exchange can significantly affect the evolution of biogeochemical processes in the hyporheic zone for a gaining stream by, for example, temporally facilitating special biogeochemical processes.</p>