Water Level Variations Research Articles

Delineation of highland saline groundwater sources in Ba'kelalan region of NE Borneo to improve the salt-making production using geochemical and geophysical approaches

The extraction of mountain salt from the saline waters is the basic livelihood of the Ba'kelalan communities of Sarawak. The current integrated approach is the first attempt to study the sources and geochemical processes of the saline groundwaters in this mountain region. Hence, in this study, saline groundwater samples from five existing wells in different seasons were analysed for hydrochemical parameters and multi-isotope composition (δ18O, δD, δ34S, δ11B and δ37Cl). The significant increase in TDS, EC and salinity was due to seasonal variation and fluctuation in water level based on hourly, daily and monthly observations. The geochemical ratios and the statistical techniques revealed that the salinity was due to the dissolution of marine evaporites as a dominant process, coupled with other factors such as water-rock interaction, ion exchange and sulphate reduction. From the isotopic signatures, it was inferred that the origin of saline groundwater was from the intense dissolution of marine evaporites such as halite dissolution and oxidation of -sulphide (pyrite). 2D electrical resistivity and seismic refraction methods were used to identify the lithological variations, depth of potential sources of saline groundwater, and the subsurface structures. It was inferred the probability of a conductive zone at a depth of 1–14 m, from which the saline groundwater plume migrates towards the perched aquifer. The presence of subsurface faults facilitated the movement of hypersaline groundwater from the saturated zone to the surface. The outcome of the study will support the dependent community to enhance their commercial salt production.

Cascade hydropower stations short-term operation for load distribution considering water level synchronous variation

The load distribution of cascade hydropower stations is associated with the safe operation of the hydropower stations and power grids. The conventional load distribution of cascade hydropower stations does not consider the synchronous operation of the water level. The inconsistent water level variation process of cascade hydropower stations is not conducive to the safe operation of hydropower stations and power grids. Therefore, the main purpose of this paper is to introduce the concept of equal reservoir full storage rate (ERFSR) to guide the load distribution of cascade hydropower stations. In addition, hydropower is used for new energy consumption considering the advantages of the rapid start-stop in hydropower units. The load distribution model of cascade hydropower stations is established, and three cases are set to verify the universality of the proposed model in the upper reaches of the Yellow River. The results show that (1) The concept of ERFSR can effectively guide load distribution and realize water level synchronization of cascade hydropower stations. (2) The output process of each hydropower station can be basically consistent with the load process to achieve synchronous peak shaving. (3) New energy consumption has little effect on the daily water consumption of downstream cascade hydropower stations.

The importance of non-tidal water-level variability for reconstructing Holocene relative sea level

Salt-marsh sediment is an important geological archive for reconstructing Holocene relative sea level. The vertical uncertainty of these reconstructions is usually quantified as proportional to tidal range, resulting in a presumed primacy of microtidal regions for generating precise records. We analyzed hourly water-level predictions and measurements over 1983–2001 from 43 tide gauges on the U.S. Atlantic coast to quantify the (1) relationship between elevation (relative to tidal datums) and duration of inundation; and (2) relative importance of astronomical tides and non-tidal (meteorological, hydrologic, and oceanographic) processes. Non-tidal processes are more likely to exert a proportionally large influence on water levels in regions with small astronomical tides, and less likely to do so where tides are large. In some microtidal regions (e.g., Chesapeake Bay), the precision of RSL reconstructions is likely overestimated, while in regions with large tidal range (e.g., Gulf of Maine) it may be underestimated. Adopting an inundation frequency rather than predicted astronomical datum for the upper limit of salt-marsh distribution may reduce this bias. Relative sea-level reconstructions often assume constant tidal range through time, but in some microtidal regions this assumption should be expanded to explicitly describe additional stationarity of non-tidal contributions.

Unraveling the Importance of the Yangtze River and Local Catchment on Water Level Variations of Poyang Lake (China) After the Three Gorges Dam Operation: Insights From Random Forest Modeling

Investigating the contributions of the factors influencing lake water level and their related changes with regard to hydraulic facilities is vital for understanding the driving mechanism of water level variations under the manifold pressures from anthropogenic activities and climate change. In this study, a random forest (RF) model was used to investigate the changes of the relationship between water level and discharge of the Yangtze River and local tributaries in Poyang Lake, China, based on daily hydrological data from 1980 to 2018. The results indicated that RF exhibited robust capability for water level prediction in Poyang Lake, with average R2 of 0.95, 0.88, 0.92, and 0.94 for the dry, rising, wet, and recession seasons, respectively. Predictor importance analysis showed that the discharge of the Yangtze River had greater influence on the water level than the discharge of local tributaries except for the dry season in Poyang Lake, where the influence on the water level was evident with discharge less than 5,000 m3/s. The influence of the Yangtze River also showed a clear attenuation pattern as the distance from the outlet of the lake increased, where the water level was constantly regulated by the Yangtze River. In addition, the partial dependence plots also indicated that the Yangtze River discharge changes after the TGD operation have resulted in remarkable water level decreases in the wet and recession seasons, especially for the recession period. Meanwhile, a slight increase in water level was predicted under identical discharge of local catchment in the dry season, which was only concentrated in the outlet of the lake. This study indicated the RF model as a robust technique for water level predictions and attribution analysis under multiple temporal and spatial scales. Moreover, this study confirmed the uneven influences of the Yangtze River and local tributaries on water level across different seasons, gauging stations, and phases.

The Effect of Harbor Developments on Future High‐Tide Flooding in Miami, Florida

AbstractLittle is known about the effect of tidal changes on minor flooding in most lagoonal estuaries, often due to a paucity of historical records that predate landscape changes. In this contribution, we recover and apply archival tidal range data to show that the mean tidal range in Miami, Florida, has almost doubled since 1900, from 0.32 to 0.61 m today. A likely cause is the dredging of a ∼15 m deep, 150 m wide harbor entrance channel beginning in the early 20th century, which changed northern Biscayne Bay from a choked inlet system to one with a tidal range close to coastal conditions. To investigate the implications for high‐tide flooding, we develop and validate a tidal‐inference based methodology that leverages estimates of pre‐1900 tidal range to obtain historical tidal predictions and constituents. Next, water level predictions that represent historical and modern water level variations are projected forward in time using different sea level rise scenarios. Results show that the historical increase in tidal range hastened the occurrence of present‐day flooding, and that the total integrated number of days with high‐tide floods in the 2020–2100 period will be approximately O(103) more under present day tides compared to pre‐development conditions. These results suggest that tidal change may be a previously under‐appreciated factor in the increasing prevalence of high‐tide flooding in lagoonal estuaries, and our methods open the door to improving our understanding of other heavily‐altered systems.

Ocean Tides near Hawaii from Satellite Altimeter Data. Part II

Abstract In Part I, the Chebyshev polynomial fitting (CPF) method has been proved to be effective to construct reliable cotidal charts for the eight major tidal constituents (M2, S2, K1, O1, N2, K2, P1, and Q1) near Hawaii and yields accurate results which are consistent with the Finite Element Solutions 2014 (FES2014), National Astronomical Observatory 99b (NAO.99b), and TPXO9 models. In this paper, the method is extended to estimate the harmonic constants of some minor tidal constituents. The mesoscale variation correction is applied to tidal elevations from satellite altimeters to eliminate the potential influence of background mesoscale ocean noise when estimating minor tidal constituents. This correction is necessary and makes the amplitude ratio between P1 and K1 constituents more consistent with the equilibrium tidal theory. Compared with the harmonic constants directly extracted from satellite altimeter data, FES2014 and NAO.99b yield mean root-mean-square (RMS) errors of 0.238 and 0.226 cm, respectively, while CPF method yields a mean RMS error of 0.210 cm, causing a 7%–12% decrease in the RMS error. At the crossover points between ascending and descending tracks, the decrease of RMS errors becomes 15%–18%. The accuracy of this method is also validated by comparing the estimated harmonic constants with those derived from tidal gauges and bottom-pressure recorders. These results indicate that the CPF method is also effective for estimating harmonic constants of minor tidal constituents. More importantly, the CPF method can obtain the harmonic constants of minor tidal constituents directly from satellite altimeter data, instead of being inferred via admittance theory. Significance Statement Ocean tides originate from the gravitational attraction of the sun and moon. Among the large number of tidal constituents, the major tidal constituents have been extensively studied. We extend the method proposed in Part I to estimate the harmonic constants of some minor tidal constituents with low amplitudes. The method relies on actual observations of water level variations from satellite altimeters without considering the hydrodynamic equations. We compared the results of this method with those of other models, using the data from satellite altimeters, tidal gauges, and bottom-pressure recorders. We find that the method performs well in estimating harmonic constants for some minor tidal constituents and causes a decrease of 7%–18% in RMS errors compared to other models.

Hydrological and Isotopic Variability of Perched Wetlands on North Stradbroke Island (Minjerribah), Australia: Implications for Understanding the Effects of Past and Future Climate Change

Over the first two decades of the 21st century, many wetlands in eastern Australia exhibited declining water levels, causing concern for communities and environmental managers and raising questions about the roles of climate change and other human activity in these water level declines. In this context we examine the causes of water level variability in four wetlands on North Stradbroke Island (Minjerribah), in the humid subtropics of south-eastern Queensland, Australia, using a combination of hydrological and water isotope monitoring and modelling. North Stradbroke Island has a high concentration of wetlands perched above the regional water table, with cultural and ecological significance, and value for palaeoclimate research. From 2015 to 2019, wetland water depths decreased markedly at all sites, coinciding with increases in oxygen isotope ratios in surface waters. The data indicate that climate, specifically a decrease in precipitation relative to evaporation, was responsible for those declining water levels, and that groundwater extraction did not play a critical role. At two of the sites—both palustrine wetlands—declining surface water levels led to intermittent connectivity with the local perched aquifers. At the other two sites, which are both shallow lakes, the surface waters were constantly fed by perched groundwater. The hydrology of the two lakes was modelled using simple mass balance. However, in order to accurately model lake level change, it was necessary to vary catchment runoff and lake outflow via groundwater through time, highlighting complexity in projecting future hydrological change in these lakes. The long term resilience of these lakes depends on a combination of rainfall regime and the balance between catchment runoff and groundwater throughflow, the future of which is highly uncertain. As a consequence, continued efforts to project future hydroclimate and to model the complex hydrology of subtropical wetlands are essential.

RELATIONSHIP BETWEEN OVIPOSITION OF Podocnemis unifilis AND WATER LEVEL IN PERUVIAN AMAZONIAN FLOODPLAINS

In the Amazon floodplains, hydrological variability plays a crucial role by shaping the habitat, offering shelter and feeding or breeding areas. During the dry season, some fresh water turtles such as the yellow-spotted turtle (Podocnemis unifilis Troschel, 1848) use the sand banks at point bar areas as breeding sites, which must be available in time for the start of oviposition. In this study, we used altimetry-derived water level data from radar satellites combined with in-situ hydrological measurements to evaluate water level variations and relate them to oviposition starting dates (2003-2012) from Pacaya-Samiria National Reserve, Peru. Synchronous hydrological behavior was found between the major river stems (Ucayali and Marañon) and the inner rivers (Pacaya and Samiria), thus enabling the utilization of water level in the main river stem to correlate with oviposition in the inner rivers. Mean oviposition date was July 23nd with selection of a narrow water level range (92 masl ± 0.9 SD). Consistent shifts towards early/late oviposition were found for years with early/late dry season onset. Extreme biological shifts in terms of oviposition date onset, were identified for specific years (2004, 2010 and 2011) mainly for the extreme dry year of 2010.

A Real-Time Assessment of Aquatic Ecological Health Using a Process-Based Model: An Example From Lake Poyang, China

Aquatic ecological health is a global challenge due to its significant impacts, and a real-time method to accurately assess the ecological health is therefore particularly useful. Based on the hydrological, water quality, meteorological, and topographic data collected from field observations and organizations, this study developed a process-based hydrodynamic and water quality model using an environmental fluid dynamics code (EFDC) model of Lake Poyang to simulate the spatiotemporal variations in water levels and the total nitrogen (TN), total phosphorus (TP), and chlorophyll a (Chl a) contents. Compared with the measured values, the models were confirmed to be reliable and acceptable. Then, to achieve a real-time assessment, the simulated results were calculated and transformed into five ordinal rating categories by using a lake ecosystem health assessment framework. Our research revealed the following results: (1) the highest and lowest 10-day water level statuses indicated that the hydrological conditions of this lake were at “good” or “excellent” levels. (2) The health levels of TN were mostly at the “fair” level or below, and most of the real-time assessment health curves of lake zones were close to the single peak type. (3) The TP contents were often at “good” levels, and the health assessment curves of the lake zones exhibited downward trends during the periods of rapid rise or retreat. (4) A fluctuating characteristic was found in the health assessment of Chl a with at least two declining peaks in all lake zones. This study demonstrated the high value of physics-based models for assessing the ecological health of aquatic ecosystems in a robust and accurate manner.

Damming-Induced Hydrogeomorphic Transition in Downstream Channel and Delta: A Case Study of the Yellow River, China

River dynamics and sediment budget play a crucial role in shaping geomorphic variability of river channels and deltaic environments. Basin-scale human activities, including dam construction, induce alterations in river flow and sediment dynamics in the downstream channels and to the delta, and quantification of sediment source shift along downstream fluvial-deltaic systems is often uncertain. This study analyzed the river regime changes and sediment dynamics of a typical sediment-laden fluvial-deltaic system—the lower Yellow River (LYR) and the Yellow River Delta (YRD) —to assess the integrated effects of dam impoundment and dam-based river regulation schemes on downstream hydrogeomorphic transition processes. The Xiaolangdi (XLD) Reservoir, which was completed in 2000 with a total storage of 12.7 km3, is the final reservoir located in the middle Yellow River and plays an important role in flood control and energy supply. Following the full operation of XLD Reservoir, the relationship between water and sediment in the LYR became more balanced, with a drastic decline of sediment input and seasonal migrations of floodwaters. The interannual variability of water levels at downstream hydrological stations indicated a geomorphic transition in the LYR from net deposition to erosion state. The building of the XLD Reservoir caused a downstream shift of river-originated sediment source and 48% of the total sediment delivered to the YRD was derived from the LYR. However, the reduced sediment delivery since 2000 has still triggered net land loss regarding the YRD system, with a strong spatial variability which is dominated by the reduced accretion at the active delta front and erosion at the abandoned river mouth and coastal engineering zone. Compared with other environmental factors, the construction of upstream dams contributed the most to the decline of downstream sediment delivery over the past decades. The challenge for sustainable sediment management is the gradual decline of scouring efficiency as the riverbed sediment is coarsening. Our study suggests that future river regulation strategies should consider the geomorphic sustainability of both the LYR and the YRD system.

Real-Time Water Level Prediction in Open Channel Water Transfer Projects Based on Time Series Similarity

Changes in the opening of gates in open channel water transfer projects will cause fluctuations in the water level and flow of adjacent open channels and thus bring great challenges for real-time water level prediction. In this paper, a novel slope-similar shape method is proposed for real-time water level prediction when the change of gate opening at the next moment is known. The water level data points of three consecutive moments constitute the query. The slope similarity is used to find the historical water level datasets with similar change trend to the query, and then the best slope similarity dataset is determined according to the similarity index and the gate opening change. The water level difference of the next moment of the best similar data point is the water level difference of the predicted moment, and thus the water level at the next moment can be obtained. A case study is performed with the Middle Route of the South-to-North Water Diversion Project of China. The results show that 87.5% of datasets with a water level variation of less than 0.06 m have an error less than 0.03 m, 71.4% of which have an error less than 0.02 m. In conclusion, the proposed method is feasible, effective, and interpretable, and the study provides valuable insights into the development of scheduling schemes.

Water-Level Fluctuations and Water Temperature Effects on Young-of-Year Largemouth Bass in a Southwest Irrigation Reservoir

Abstract The effects of a warming climate will alter the hydrological cycles of arid southwestern U.S. reservoirs which primarily support agricultural needs, provide flood control, and generate hydroelectric power while secondarily supporting fish communities and sport fishing opportunities. The success of littoral spawning fishes depends on the timing and variability of water levels. The onset of drought between 2017 and 2018 provided an opportunity to evaluate the timing of hatch dates and relative abundance of young-of-year Largemouth Bass Micropterus salmoides across two water years of varying water temperatures and water levels in a southwestern U.S. reservoir. A retrospective analysis of otoliths in young-of-year Largemouth Bass revealed similar hatch dates in 2017 (14 April–29 May) and 2018 (13 April–28 May) despite differences in water temperature and water level rate of change. Median water temperature during hatch dates was greater in 2017 (median 19.0°C, range 14.3–24.4°C) than 2018 (17.6°C, range 13.5–21.7°C). Water level rate of change during hatch dates in 2017 was positive (+3.1 to +13.1 cm/d), which reflected reservoir filling. In contrast, water level rate of change during hatch dates in 2018 was negative (−8.5 to −0.6 cm/d), which reflected reservoir receding. Relative abundance of young-of-year fish was greater in 2017 (21.7 fish/h) when the reservoir was filling compared with relative abundance in 2018 (6.8 fish/h) when the reservoir was receding. The median growth rate was greater in 2017 (1.02 mm/d) when the reservoir was filling than in 2018 (0.82 mm/d) when the reservoir was receding. Despite differences in water temperature and contrasting reservoir levels between the two water years, the Largemouth Bass population in a southwest U.S. reservoir exhibited similar hatch dates reported for the species in southeastern and northeastern U.S. reservoirs. While water demand in the 21st century may exceed availability, the opportunity exists to collaborate with water managers to benefit Largemouth Bass populations in southwestern reservoirs.

Spatial and seasonal water level dynamics in dryland grabens along the Rift Valley of northern Ethiopia

ABSTRACT We investigated water levels in semi-closed grabens of northern Ethiopia. Springs (n = 79), streamflows (n = 48), wetlands (n = 3), endorheic lakes (n = 3), hand-dug wells (n = 48) and boreholes in unconfined aquifers (n = 25) were monitored (2015–2017). Spring discharge fluctuates between wet (2.75 ± 1.5 L/s) and dry seasons (0.87 ± 0.21 L/s) (n = 68, p < .0001). Spring discharge and streamflow were larger at the foot of the escarpment than at the horst (p < .001). The water level of wells varied between horsts and escarpments in the grabens (p < .02). A water level depletion of up to 2.23 m/year occurred in response to withdrawals in the irrigated plains. Importantly, water level fluctuation was faster in streams, springs and hand-dug wells than in boreholes. Striking water level variations in the grabens were linked to rainfall deficit and management scarcity. An integration of surface water and groundwater management responses will bring the water table nearer to the surface; this could mitigate water storage in the fertile and productive grabens.

Analysis of the water color transitional change in Qinghai Lake during the past 35 years observed from Landsat and MODIS

Study regionQinghai Lake, Qinghai-Tibet Plateau, China Study focusWater color has been recognized as an essential climate variable for lakes and oceans. Forel-Ule index (FUI), as one representative water color quantization parameter, is a useful indicator that shows water turbidity variations in lakes. In this study, the time series of FUI images were constructed for Qinghai Lake, the largest salt water lake in China, from 1986 to 2020 based on Landsat and Moderate Resolution Imaging Spectroradiometer (MODIS) data. The multi-source satellite data were first evaluated and compared with regard to the derivation of FUI; then, the spatial and temporal variations of water color in Qinghai Lake and its driving forces were analyzed. New hydrological insights for the regionThe results revealed that the FUI showed a significant decreasing trend in Qinghai Lake from 1986 to 2004 and a significant increasing trend from 2004 to 2020, which temporally coincided with the water level variations in Qinghai Lake. The water level, water temperature, precipitation, and runoff were strongly correlated with the changes of FUI (correlation coefficients of 0.65–0.78). The substantial increases in precipitation and water temperature after 2004 can be the major causes for the transitional increase of water color in Qinghai Lake. This reflects one response mode of water quality in lakes to climate change.

Components of urban ground water recharge in Bengaluru, India

ABSTRACT This study investigates the various components of groundwater recharge in an urban hard-rock aquifer system of Bengaluru, India. Groundwater meets more than fifty percent of the water demand in the city. This has led to an endangered situation of groundwater. Urbanization changes the source and path of groundwater recharge. Understanding the components of groundwater recharge is the foremost important step in groundwater management in an urban environment. Rotated empirical orthogonal function (REOF) analysis of ground water level data was used to identify the significant components of ground water level variation in the study area. Rainfall and pipeline leakage were identified as the major components of groundwater recharge in the study area. The stochastic interpolation method of ordinary kriging was used to regionalise the identified significant empirical orthogonal functions.

The hydrochorous dispersal of plant propagules in a giant river reservoir: Implications for restoration of riparian vegetation

Abstract The riparian vegetation of many rivers around the world is impacted by flow regulation for hydropower. Water levels behind dams are being raised to generate electric energy, forming river reservoirs. River regulation has a large impact on the riparian vegetation, which influences both the adjacent aquatic and terrestrial ecosystems. Therefore, the restoration of degraded riparian vegetation in river reservoirs has been of increasing research interest. Propagules dispersed from connected tributaries via water (hydrochory) are considered a vital source for the recovery of riparian vegetation in regulated rivers. However, the hydrochorous dispersal of plant propagules in river reservoirs is unclear. We explored the dispersal distance and deposition patterns of hydrochorous propagule mimics in three tributaries that are regulated by the Three Gorges Reservoir (TGR) in China. In eight out of nine release experiments, 95% of propagule mimics were found within 3 km downstream from the release points. Cumulative wind speed was the most important factor affecting the dispersal distance of propagule mimics in the TGR. However, the dispersal distance of propagule mimics was not significantly affected by water‐level variation and channel sinuosity. Variations in water level strongly affected the deposition pattern of propagule mimics, with only 6.6% of the propagule mimics stranding on the riparian zones under raised water level and 83.8% stranding under declined water levels. The majority of stranded propagule mimics were deposited at gentle slopes (0–20°). Synthesis and applications. Our results suggest that the majority of propagules that enter river reservoirs via water would be retained within the first few kilometres. Wind and water level variation are the main factors determining the dispersal distance and deposition pattern of propagules. Our findings have applications for riparian vegetation restoration in river reservoirs. The vegetation in steep riparian zones distant from free‐flowing tributaries should be the priority for restoration actions because these areas receive limited hydrochorous propagules. The plant biodiversity and hydrological connectivity of connected tributaries, which is an important propagule sources, should be protected. The seasonal dominant wind pattern should be considered when evaluating the importance of tributaries as the source of hydrochorous propagules for river reservoirs.

A learning-based approach towards the data-driven predictive control of combined wastewater networks – An experimental study

Smart control in water systems aims to reduce the cost of infrastructure expansion by better utilizing the available capacity through real-time control. The recent availability of sensors and advanced data processing is expected to transform the view of water system operators, increasing the need for deploying a new generation of data-driven control solutions. To that end, this paper proposes a data-driven control framework for combined wastewater and stormwater networks. We propose to learn the effect of wet- and dry-weather flows through the variation of water levels by deploying a number of level sensors in the network. To tackle the challenges associated with combining hydraulic and hydrologic modelling, we adopt a Gaussian process-based predictive control tool to capture the dynamic effect of rain and wastewater inflows, while applying domain knowledge to preserve the balance of water volumes. To show the practical feasibility of the approach, we test the control performance on a laboratory setup, inspired by the topology of a real-world wastewater network. We compare our method to a rule-based controller currently used by the water utility operating the proposed network. Overall, the controller learns the wastewater load and the temporal dynamics of the network, and therefore significantly outperforms the baseline controller, especially during high-intensity rain periods. Finally, we discuss the benefits and drawbacks of the approach for practical real-time control implementations.

Hydrological Characteristics Change of Hala Lake and Its Response to Climate Change, 1987–2018

Lakes on the Tibetan Plateau (TP) are an indicator of global climate change. The study on the factors driving lake change on the TP can help us understand its response to climate change. In this study, Landsat and ICESat data were used to obtain the variations of area, water level, and storage of Hala Lake and the area of glaciers in the Hala Lake Basin during 1987–2018. Combined with meteorological data, climate change trends and the factors driving Hala Lake change in the last 30 years were analyzed. The contribution of glacier mass loss to lake recharge was estimated by the water balance of Hala Lake. The results showed that Hala Lake has experienced three stages: slight expansion (1987–1994), shrinkage (1995–2001) and rapid expansion (2002–2018) during the study period. The rate of glacial melting continued to decline during the study period. Precipitation was the main factor that drove the hydrological characteristic changes in Hala Lake. The step change points of annual precipitation and temperature occurred in 2001, almost the same time that Hala Lake began expanding rapidly.

Relationships among Seepage, Water Level, and Rainfall of a Fill Dam by Decision Tree Analysis

This study is to present acceptable measurement values through decision tree analysis for the seepage, which is an important measuring item of the fill dam. The seepage of the dam under study increases rapidly when rainfall occurs, when the direct inflow of rainfall from the downstream slope and both sides occur. Therefore, the allowable seepage of fill dam considering rainfall and water level is required. Decision tree analysis was conducted for one domestic fill dam by setting the seepage as a response variable and setting rainfall and water level as explanatory variables. At this time, in order to analyze the effects of rainfall on the seepage more closely, the data subject was classified into two groups consisting of a rainfall-free group and a rainfall-occurring group. Group A, which is a rainfall-free group, had 97.7% of the seepage data distributed under the conditions of 98.50 mm/day of the antecedent 5-day rainfall selected as the first explanatory variable. The average seepage of the group was between 12.01 L/min and 26.35 L/min. Group B, which is a rainfall-occurring group, had 85.7% of the water leakage data distributed under conditions of 38.50 mm/day of daily rainfall selected as the first explanatory variable, with an average of 23.70 L/min.

Conceptual analysis of seepage control for Senggarang Coastal Embankment with chemically-stabilized backfill

One of the common problems of coastal embankments is water seepage. The Senggarang Coastal Embankment (SCE) is examined in the present work, with the objective of proposing the improvement of the earth structure via chemical stabilization. The stabilized soil embankment was simulated and analyzed with PLAXIS 8 to identify a conceptual proposition of solution using a conventional and innovative stabilizer, i.e., lime-ZnO and cement-CSP (cockle shell powder). The base of the embankment was assumed to be bedrock, in order to eliminate the passage of water below the embankment. Stabilization was taken as 100 % for the embankment, i.e., a homogeneous earth structure made entirely of stabilized soil for seepage mitigation. Input parameters for the simulations were acquired from both field samples and past studies. Varying water levels due to tidal effect were applied in the model to determine the changes of pore pressure distribution which could potentially lead to instability of the embankment. As water level increases with the rising tide, total displacement of the original earth embankment was found to increase as the soil weakened, with decreasing effective shear stress. Replacement of the embankment backfill with cement-CSP and lime-ZnO were both observed to significantly reduce the displacements. The use of both stabilizers not only improves the SCE’s engineering performance in terms of reduced water seepage and displacement, accompanied by increased strength, but the ‘green’ nature of the former, as derived from organic waste, also enhances the appeal of the stabilization technique.