Optimal location of cutoff walls for seawater intrusion

In this paper, the simulation–optimization method is used to study the optimal location of cutoff walls for seawater intrusion. The optimization model is based on minimizing the chlorine concentration of two water sources after 50 years. In order to reduce the computational complexity, a Kriging surrogate model simulation is coupled with the optimization model. Finally, a hypothetical case is used to evaluate the accuracy of the surrogate model and the performance of the optimization model. The results show that the outputs of the Kriging surrogate model and the variable density groundwater simulation model for the same cutoff wall design fit well, and the average relative error of the two outputs is only 2.2% which proves that it is feasible to apply the Kriging surrogate model to this problem. By solving the optimization model, the location of the cutoff wall which minimizes the sum of chlorine concentration of the two water sources after 50 years is obtained. This provides a stable and reliable method for the site selection of cutoff walls for future projects intended to prevent and control seawater intrusion.

Investigating Seepage Paths at Golfaraj Earthen Dam, Northwest Iran

An investigation of seepage was conducted at Golfaraj Reservoir Dam with a particular emphasis on determining the seepage areas based on regional and site-specific hydrogeological studies. The primary goal of the investigation was to develop strategies intended to minimize dam and reservoir seepage. Leakage from the reservoir is a serious problem and of considerable concern to the local populace. Substantial reduction of seepage from Golfaraj Reservoir Dam is the ultimate goal of the investigations conducted. Golfaraj Reservoir Dam, located in East Azerbaijan province, northwest Iran, was built to provide water for agricultural and industrial needs in Golfaraj plain and neighboring lands. The Golfaraj Reservoir was constructed through the Miocene Upper Red Formation, which consists of sequences of sandstone, mudstone, conglomerate, and gypsiferous marl. Following reservoir filling, seepage of water into adjacent formations was found to occur at an estimated rate of 70 L/s. After reservoir impoundment groundwater levels in Shahmar village, 2 km downstream and just north of the dam axis, rose and land surfaces became abnormally wet. Lugeon values in some boreholes drilled around Golfaraj Dam before and after dam construction were high enough to indicate that the dam base has sufficient permeability to allow water to escape by underflow. Twenty-four Casagrande piezometers installed around the dam axis at four sectors provided additional information on seepage pathways through the dam body and underneath or through the cutoff wall. Water-level variations in the Casagrande piezometers confirmed the seepage routes. Study results showed that reservoir water likely seeps through the reservoir bottom and beneath and through the cutoff wall. The west side of the dam and near the reservoir reflected water-level rises in accordance with the rise in reservoir-water level. Seepage in this area is probably due to its proximity to Golfaraj Reservoir. Hydrogeochemical analyses further suggest that the water source of Shahmar Drain, ~ 1800 m north of Golfaraj Dam cannot be from the east or west embankments of the dam because the electrical conductivity in Shahmar Drain water approximates the electrical conductivity of Golfaraj Reservoir water and is lower than the electrical conductivity of groundwater in some of boreholes. Potential future seepage mitigation measures will focus on methods to seal the reservoir floor and cutoff wall sections I2-I2 and I3-I3, although some efforts may be directed at the west side of the dam. Such measures could take the form of installation of a geomembrane barrier over the west side of the dam, concrete cutoff walls downstream of the dam, and pumping wells to intercept seepage.Thematic collection: This article is part of the Sustainability in engineering geology and hydrogeology collection available at: https://www.lyellcollection.org/cc/sustainability-in-engineering-geology-and-hydrogeology

Numerical Evaluation of a 70-m Deep Hydro-Power Station Foundation Pit Dewatering

The average depth of Yamansu hydropower station foundation pit is 70 m. The foundation pit was excavated with five-level slopes. The lowering of groundwater level is significant for excavation. Drainage and pumping were adopted in dewatering. Pumping tests were performed to reverse hydraulic parameters and calibrate numerical models. Numerical simulations were performed to evaluate the dewatering scheme. In the first stage, powerhouse tailrace canal was excavated and utilized as a drainage channel to lower the groundwater level. The drawdown and hydraulic gradient were evaluated to prevent potential water inrush, erosion, piping, and slope failure. In the second stage, cutoff wall and pumping wells were evaluated to lower the groundwater level. The influences of depth, permeability, and thickness of the cutoff wall were evaluated. Dewatering scheme was revised accordingly based on the evaluation. The optimized dewatering scheme, which can be referred by similar engineering, was performed and verified successfully.

Apron and Cutoff Wall Scour Protection for Piano Key Weirs

Piano key (PK) weirs are used in a variety of flow control structure applications, including spillway crests and open channel diversion structures. However, to the best of authors’ knowledge, structure-specific design guidance for scour mitigation is still needed. To fill this gap of knowledge, a systematic experimental campaign was conducted by testing different configurations of horizontal aprons with a cutoff wall. Protection structures were located at the toe of the PK weir. Namely, experiments were performed at large-scale to assess the effect of three apron lengths on downstream scour hole geometry under different hydraulic conditions. It was observed that a horizontal apron deflects the plunging jets originating from the PK weir, thus significantly reducing scour. Experimental evidence allowed corroboration that significant scour depth reduction occurs for an apron length 1.5 times the weir height, with longer aprons found to provide marginal benefits. Finally, also provided herein are tools to estimate the main scour characteristics and help practitioners in optimizing apron design.