Soil dwelling termites dig nests in the ground that have a significant impact on the soil environment. Activities of termites can result in accumulation of organic matter and enrichment of nutrients and minerals in the soil. Samples from the nest/surrounding soils of two termite species (Odontotermes formosanus (Shiraki) and Reticulitermes flaviceps (Oshima)) and termite non-invaded soils in the seawall of the Qiantang River, Zhejiang Province, China were collected and analysed for soil pH. The results show that the observed termites prefer an acidic environment and that their activities elevate the pH of termite mound soil compared with surrounding soil. Considering the differences in the distribution areas, termite species, and properties of termite mounds and surrounding soils, this paper also examines the literature concerning the effects of termites on soil pH. After summarizing the pH of the termite survival soil environment, the feasibility of termite control by modifying the soil pH is addressed. Finally, some topics for future research are discussed.

Tidal bores are a natural phenomenon with high flow velocity and destructive potential. A spur dike is a widely used river regulation and embankment protection structure that minimizes erosion, promotes deposition, and protects riverbanks. However, the scouring mechanism around a spur dike under the action of a tidal bore is not fully understood, and accurately estimating the maximum scour depth has always been a challenge, limiting the construction and maintenance of spur dikes in estuarine and marine environments. This study analyzed the scouring characteristics around a spur dike induced by tidal bores via field observation and model experiments. The results show that the scours around a spur dike can be divided into dike head scour and upstream side scour. The scour depth is related to the geometric shape of the spur dike and its surrounding riverbed, hydrodynamic forces, and sediment characteristics. The least squares method obtained the fitting formulas for the depth of the scour at the dike head and upstream side. Overall, the present study indicates an agreement of the scouring characteristics around a spur dike between the field observations and laboratory experiment, and the fitting formulas can be effectively applied to engineering practices of a macro-tidal estuary.

Tidal bores are natural phenomena resulting from the nonlinear distortion of tidal waves and propagate upstream with the incoming tide. The Qiantang River tidal bore is world-famous for its great momentum which can occasionally inflict major damage to infrastructures in the Qiantang River Estuary, China. Existing design guidelines are not fit for accurately estimating the tidal bore loads on elevated structures. This study investigated the impact of tidal bores on the trestle piers of a river-crossing bridge using field tests. Based on the measured data, empirical formulas for the maximum impact pressure in four zones across the trestle were derived, and the influence of the Froude number on the peak pressure was determined. Results show that the peak pressure of the instantaneous impulsive state of the bore can exceed the pressure of the quasi-steady state 10-fold. The maximum dynamic impact pressure on the seaward side of the pier occurs at the base of the bore. The peak dynamic pressure accounts for 54%, 45%, and 20% of the total pressure for Froude numbers of 1.26, 1.12, and 1.04, respectively. The results of this study can serve as valuable references for the load design of structures against tidal bores and tsunami-like waves.

A tidal stream energy resource assessment can be achieved through direct measurements of tidal elevations or flow velocities, theoretical formulas, and numerical models. This paper first described the development of renewable energy in China. Then, the tidal stream energy resource in the Qiantang River Estuary was assessed. The present work established a 2D numerical model for calculating the power density in the estuary and validated it with in situ water level, tidal current, and suspended sediment concentration measurements. Three possible sites found near the Hangzhou Bay Bridge were selected for detailed resource assessment. The results indicated that if only 50 turbines are deployed to each site, the tidal stream energy output by all turbines would be 7.5 GWh/year. Finally, building a tidal stream power generation device into an existing bridge structure was proposed at the Qiantang River Estuary.

Subterranean termite activity can increase the hydraulic conductivity and water infiltration of filling soil, and therefore affects the stability of an earth embankment and subsequent safety. As a physical barrier for sustainable termite management, NaCl-laden soil barrier (NLSB) is a promising alternative for subterranean termite control in earth embankments. This novel technology can prevent tunneling and penetration of subterranean termites into the interior of an embankment and has been widely employed for more than 20 years in Zhejiang Province, China. The efficacy and longevity of NLSB depend on the long-term presence of NaCl concentration in soil barriers. The aim of this study is to develop an understanding of water flow and salt transport in NLSB based on the two-dimensional Richards’ equation and convection dispersion equation using the HYDRUS software package. Conceptual and numerical models of NLSB are modeled using scenario analysis according to water level fluctuations, saturated hydraulic conductivity, and rainfall infiltration conditions. Furthermore, the center and spread variance of a solute mass over a 100-year period are quantified using moment analysis. As flood frequency, saturated hydraulic conductivity, and rainfall infiltration flux increase, salt desalination in NLSB significantly increases. When the rainfall infiltration flux is 1% of the annual average rainfall, the total amount of salt transport and leaching can increase by 55%. Moreover, these results facilitate better long-term sustainable management of existing sites and optimal design of future NLSBs.