Reservoirs In Taiwan Research Articles

An assessment of long-term overtopping risk and optimal termination time of dam under climate change

Reservoir management faces a wide range of new challenges resulting from the impact of climate change. One set of challenges arises from the non-stationary nature of hydrological conditions. Another crucial issue is watershed sedimentation, which can significantly influence the sustainability and safety of reservoirs. To address these concerns, this study developed a framework for the management of reservoir risk. An analytical conceptual model coupling physical governing relationships and economic tools was proposed, which was then applied to the Shihmen Reservoir in Taiwan. We adopted a statistical representation of future hydrologic conditions with the assumption of time-variant moments and focused on evaluating the impact of an increase in the frequency of extreme hydrological events caused by climate change and used a stochastic approach to quantify the risk factors. Our results confirm that this approach can be used to identify reservoir-related risks and generate appropriate options for strategy and policy.We determined that the major source of risk is the hydrological conditions, especially the extreme events. More severe intra-annual climatic change is much more dominant in the risk compared to inter-year trends. The influence of reservoir characteristics on risk is associated mainly with the availability of flood control capacity, but limited due to the limitation of its volume and potential to regulate the flow. Engineering may provide an option for mitigating the risk, but integrated, watershed-level approaches, such as providing systematic detention or land use management, are better suited to reducing the storm peak from a long-term perspective. With a critical increase in the risk of overtopping, a high probability of dam failure and corresponding losses may precipitate the need to retire or remove the facility. However, because the benefits and costs are both huge, the decision may be biased by a conservative attitude. The outcome of small facilities failing may be considered more acceptable than similar events besetting larger systems.

Effects of increasing nutrient supply and omnivorous feeding on the size spectrum slope: a size-based nutrient-phytoplankton-zooplankton model

Size spectrum slope has been considered as an indicator for system productivity and size-dependent trophic interactions in plankton communities. We investigated the effect of new nutrient flux (Nin) and feeding breadth of zooplankton (σ2) on spectral slopes of the plankton community using a size-structured nutrient-phytoplankton-zooplankton model. We studied two types of plankton systems (1) at a steady state and (2) with fluctuating plankton populations. For the steady state systems, the spectral slopes increased with Nin and σ2. In contrast, for the systems in fluctuation, spectral slopes constructed from long-term average plankton populations decreased with increasing Nin and σ2. In addition to spectral slopes constructed from long-term average population densities, we investigated slope variability in systems with fluctuating plankton populations. The variability of spectral slopes was found to increase with Nin and σ2, indicating that spectral slope variation is large in a eutrophic system or when zooplankton feed on a wide size range of prey. Empirically, because Nin is difficult to measure, nutrient concentration is investigated instead. Our model predicts that the spectral slope is positively correlated with nutrient concentration due to the accumulated mesozooplankton biomass, which was confirmed by our study in plankton community in a subtropical reservoir in Taiwan.

Characterization of reservoir sediment under water with differential pressure-sensored flat dilatometer and piezo-penetrometer

The unusually strong typhoons and heavy rainfalls occurred recently in Taiwan have caused major landslides in many reservoir catch basins. The debris from these landslides eventually settled in the reservoir and turned into mud. From soil mechanics point of view, the mud immediately in front of the dam where the reservoir is usually the deepest is a very young, normally consolidated or under-consolidated fine-grained soil. The engineering properties of the reservoir mud are important parameters in the planning and design of schemes to remove the mud. Yet, our knowledge in this regard is very limited. For some of the major reservoirs in Taiwan, the mud is often under more than 40 m of water. How to conduct effective geotechnical site characterization under these circumstances is a challenge. The authors developed techniques to incorporate differential pressure measurements in flat dilatometer (ΔDMT) and piezo-penetrometer (ΔPu) tests to facilitate in situ measurements under water in a reservoir. A series of field ΔDMT and ΔPu tests along with representative soil sampling were conducted at Tsengwen Reservoir in southern Taiwan. The paper describes the techniques of ΔDMT and ΔPu tests, interpretation of available test data to obtain the engineering properties of the reservoir mud, and discusses implications in the future site characterization of reservoir mud.

The Application of Light Weight Aggregate Using Reservoir Sediments for Concrete Filled Columns

In the current 2005 AISC specification, the in-filled light-weight concrete strength (fc´) of concrete-filled tube (CFT) columns is set in the range of 21~ 42 MPa, but with no real substantial testing data to confirm and verify the provisions. Research work related to rectangular column sections with light-weight concrete is rather limited and deserves further investigation. Eighteen rectangular tubes filled with light-weight concrete with fc´ varying from 21.4 to 43.5 MPa were tested. A special kind of light weight aggregate using find sediment deposits dredged from a local reservoir in Taiwan were used in this experimental study. Formulas for CFT columns as specified in the design code AISC Specification were examined and compared. The test results actually show that the further lower fc´ values are possible and that the 1999 AISC-LRFD provisions yields conservative design results. For the fc´ range specified in the 2005 AISC specification is found to be in good agreement with the test results

A Research of Reservoir Sediment Solidification Using Biotechnology

At the end of 2010, almost all reservoirs in Taiwan have sedimentation problem. Sedimentation in major reservoirs, such as Wushoh reservoir, had reached 63.73% of its storage capacity in 2009, and must undergo dredging. However, agencies responsible for the final processing stages of reservoir sediments failed to come up with a breakthrough. Limitations established by environmental protection laws also hindered proper dredging of the reservoirs. Hence, further investigation was required for solidifying and reusing reservoir sediments. This research focused on the reuse of Wushoh reservoir sediments. Experimental results showed that when bacteria Bacillus Pastuerii(B.P.) was utilized in sediment solidification, higher bacterial concentrations could induce higher sedimentation of calcium carbonate. In a 70% Urea-CaCl2 medium, a bacterial concentration of 100% resulted in the highest compressive strength that was 30% higher than the control group (bacterial concentration of 0%). Therefore, bacteria can be used to solidify sediments and improve compressive strength. In specimens treated with higher concentrations of bacteria, more square and polygonal crystals were observed via SEM. X-ray powder diffractometer (XRD) analysis showed that bacteria-treated sediments contained calcium carbonate crystals in every stage of processing. Hence, it was shown that bacteria can promote solidification by inducing calcium carbonate sedimentation.

Estimation of phosphorus flux in rivers during flooding

Reservoirs in Taiwan are inundated with nutrients that result in algal growth, and thus also reservoir eutrophication. Controlling the phosphorus load has always been the most crucial issue for maintaining reservoir water quality. Numerous agricultural activities, especially the production of tea in riparian areas, are conducted in watersheds in Taiwan. Nutrients from such activities, including phosphorus, are typically flushed into rivers during flooding, when over 90% of the yearly total amount of phosphorous enters reservoirs. Excessive or enhanced soil erosion from rainstorms can dramatically increase the river sediment load and the amount of particulate phosphorus flushed into rivers. When flow rates are high, particulate phosphorus is the dominant form of phosphorus, but sediment and discharge measurements are difficult during flooding, which makes estimating phosphorus flux in rivers difficult. This study determines total amounts of phosphorus transport by measuring flood discharge and phosphorous levels during flooding. Changes in particulate phosphorus, dissolved phosphorus, and their adsorption behavior during a 24-h period are analyzed owing to the fact that the time for particulate phosphorus adsorption and desorption approaching equilibrium is about 16 h. Erosion of the reservoir watershed was caused by adsorption and desorption of suspended solids in the river, a process which can be summarily described using the Lagmuir isotherm. A method for estimating the phosphorus flux in the Daiyujay Creek during Typhoon Bilis in 2006 is presented in this study. Both sediment and phosphorus are affected by the drastic discharge during flooding. Water quality data were collected during two flood events, flood in June 9, 2006 and Typhoon Bilis, to show the concentrations of suspended solids and total phosphorus during floods are much higher than normal stages. Therefore, the drastic changes of total phosphorus, particulate phosphorus, and dissolved phosphorus in rivers during flooding should be monitored to evaluate the loading of phosphorus more precisely. The results show that monitoring and controlling phosphorus transport during flooding can help prevent the eutrophication of a reservoir.

Statistical evaluation of the effect of earthquake with other related factors on landslide susceptibility: using the watershed area of Shihmen reservoir in Taiwan as a case study

Landslide susceptibility evaluation is one of the most important issues in watershed management. After an earthquake, the landslide susceptibility decreases functionally with increases in the distance from the epicenter. Under the same rainfall intensity, landslides are more likely to occur in an area where earthquakes occur more frequently. However, the questions of how much an earthquake should be weighted and how to evaluate the effects of an earthquake still need to be studied. To understand how earthquakes affect rainfall-triggered landslides, the horizontal peak ground acceleration (PGA) data from the Central Weather Bureau Seismic Network is used as the earthquake factor and combined with other factors to determine the weight of earthquakes in landslide susceptibility using logistic regression. The results indicate that the ability of landslide prediction is better when considering the earthquake factor. This study also proved that although there are no co-seismic landslides (after earthquakes) in the study area, the earthquake factor is still required to increase the model accuracy. PGA has been described as a usable factor. In areas with frequent earthquakes and high geological activity, when using historical data to evaluate landslide susceptibility, the earthquake factor should be taken into consideration to prevent errors.

Measurement of cyanobacteria using in-vivo fluoroscopy – Effect of cyanobacterial species, pigments, and colonies

The effect of instrument calibration range, algal growth phase, chlorophyll-a and turbidity interference and colony size, on the measurement of phycocyanin by in-vivo fluoroscopy (IVF) was investigated. The cyanobacterial species Microcystis aeruginosa PCC 7820, Anabaena circinalis and Planktothricoides raciborskii were used to investigate variation in phycocyanin content in the different cyanobacteria and growth phases. The green alga, Chodatella sp., and Kaolin particles were used as the sources of chlorophyll-a and turbidity respectively to determine how these factors can impact on phycocyanin measurements. Another cyanobacterium, M. aeruginosa PCC 7005, which forms large colonies, was used to investigate the relationships between colony size and phycocyanin concentration measured using IVF. Results showed that chlorophyll-a, turbidity, and the colonial status of the cyanobacteria significantly interfered with the measurement of phycocyanin fluorescence. Models were developed to compensate for the effect of chlorophyll-a, turbidity and colony size on the measurement. The models were successfully used to correct phycocyanin probe data collected from several reservoirs in Taiwan to establish good correlation between measurements made using the phycocyanin probe and microscopic cell counts.

Effects of humic acid and suspended soils on adsorption and photo-degradation of microcystin-LR onto samples from Taiwan reservoirs and rivers

This article covers the adsorption capacity of microcystin-LR (MC-LR) onto natural organic matter (NOM) or suspended solids of water samples from reservoirs (Emerald and Jade reservoirs) and rivers (Dongshan, Erhjen and Wukai rivers) in Taiwan to determine the fate, transport behavior and photo-degradation of microcystins in natural water systems. Langmuir adsorption and photo-degradation studies were carried out and the capability of samples for MC-LR adsorption was confirmed. Among these, samples collected from reservoir showed enhanced MC-LR adsorption than that of river samples and the greater adsorption behavior was always favored by larger content of organic matter and suspended particles in the system. It is obvious from the experimental results that the adsorption of MC-LR was influenced by suspended particles (turbidity), humic acid (HA), organic matter content and other pollutants. The effective photo-degradation of MC-LR was achieved using higher energy, lower wavelength (254nm) UV light within 60min. The presence of humic acid and turbidity affected the photo-degradation process. These data provide important information that may be applied to management strategies for improvement of water quality in reservoirs and rivers and other water bodies in Taiwan.

Multi-objective game-theory models for conflict analysis in reservoir watershed management

This study focuses on the development of a multi-objective game-theory model (MOGM) for balancing economic and environmental concerns in reservoir watershed management and for assistance in decision. Game theory is used as an alternative tool for analyzing strategic interaction between economic development (land use and development) and environmental protection (water-quality protection and eutrophication control). Geographic information system is used to concisely illustrate and calculate the areas of various land use types. The MOGM methodology is illustrated in a case study of multi-objective watershed management in the Tseng-Wen reservoir, Taiwan. The innovation and advantages of MOGM can be seen in the results, which balance economic and environmental concerns in watershed management and which can be interpreted easily by decision makers. For comparison, the decision-making process using conventional multi-objective method to produce many alternatives was found to be more difficult.

Site selection for carbon dioxide geological storage using analytic network process

This paper presents an analytic network process (ANP) approach for the selection of potential sites for CO2 geological storage as basis for further exploring geological features and simulation of transport characteristics. Site selection for CO2 geological storage in this study can be considered as a complex multi-criteria decision-making problem, and thus a multi-criteria decision model with eight evaluation criteria is proposed. ANP is applied to site selection and is characterized by interdependencies among decision structure components. An illustrative example in the geological field of oil and gas reservoirs in Taiwan is presented to demonstrate ways to select and rank the most appropriate site in terms of storage capability. The results obtained in this study have proven that ANP-based approach is a useful tool in pre-screening potential sites for CO2 geological storage, enabling decision-makers to facilitate CO2 storage within climate policy.

Evaluating the Compaction Quality of Backfills by Stress Wave Velocities

Abstract In engineering practices, sand-cone tests are usually performed to assess the compaction quality of backfilled materials of highway embankments or earth dams. However, performing the sand-cone test is time consuming and can only obtain the physical but not the engineering properties of backfills. The objective of this paper is to investigate the feasibility of evaluating the compaction quality of backfills using stress wave propagation velocities. To achieve this goal, a backfill material with low plasticity used in the earth dam of the Hushan Reservoir in Taiwan was collected and tested. The calibration curves for the relationship among moisture content, dry density, and stress wave velocities were obtained. In order to verify the validity of the laboratory calibration curves, field tests were also performed on a trial embankment at the site of the reservoir. Comparing with values measured in the field using the traditional sand-cone test, the proposed method underestimates the water content and overestimates the dry density of the compacted backfills. The resulting error is less than 10 %. It is thus concluded that the proposed method is a promising tool for the evaluation of the compaction quality of backfills.

Multi-tier interactive genetic algorithms for the optimization of long-term reservoir operation

Genetic algorithms (GAs) are well known optimization methods. However, complicated systems with high dimensional variables, such as long-term reservoir operation, usually prevent the methods from reaching optimal solutions. This study proposes a multi-tier interactive genetic algorithm (MIGA) which decomposes a complicated system (long series) into several small-scale sub-systems (sub-series) with GA applied to each sub-system and the multi-tier (key) information mutually interacts among individual sub-systems to find the optimal solution of long-term reservoir operation. To retain the integrity of the original system, over the multi-tier architecture, an operation strategy is designed to concatenate the primary tier and the allocation tiers by providing key information from the primary tier to the allocation tiers when initializing populations in each sub-system. The Shihmen Reservoir in Taiwan is used as a case study. For comparison, three long-term operation results of a sole GA search and a simulation based on the reservoir rule curves are compared with that of MIGA. The results demonstrate that MIGA is far more efficient than the sole GA and can successfully and efficiently increase the possibility of achieving an optimal solution. The improvement rate of fitness values increases more than 25%, and the computation time dramatically decreases 80% in a 20-year long-term operation case. The MIGA with the flexibility of decomposition strategies proposed in this study can be effectively and suitably used in long-term reservoir operation or systems with similar conditions.

FLEXURAL BEHAVIOR AND SIZE EFFECT OF FULL SCALE REINFORCED LIGHTWEIGHT CONCRETE BEAM

This article presents the results of experimental investigations on the size effect and the flexural behavior of full size reinforced concrete beams with lightweight aggregate and normal aggregate. The lightweight aggregate (LWA) was manufactured with fine sediments collected from the Shih-Men Reservoir in Taiwan. A total of 6 flexure beams with various reinforcement ratios (from 0.33% to 1.3%) and 6 size-effect beams with various dimensions were fabricated and tested. The designed compressive strength of concrete was 34 MPa. Test results indicated that the reinforced lightweight aggregate concrete (LWAC) beams had a similar load capacity and failure mode as those of normal weight concrete (NWC) beams, but demonstrated larger ultimate deflections and curvature ductility. The curvature ductility of both types of concrete beam decreased as the reinforcement ratio increased. On the other hand, an increase of the beam dimension lead to increases of the load and deflection at the yielding strength and ultimate strength, but reduced the ultimate deflection ratio for both types of concrete beams. In addition, the ultimate deflection-to-span ratio varied from 1/115 to 1/150 (23% reduction) as the effective depth increased from 300 mm to 600 mm for the NWC beams and from 1/84 to 1/188 (55% reduction) for the LWAC beams, respectively. This reveals that the decay of ultimate deflection ratio of the LWAC beams due to the increase of beam size is more significant than that of the NWC beams.

Estimation of soil erosion rates in a subtropical mountain watershed using 137Cs radionuclide

The formulation of watershed management strategies to protect water resources threatened by soil erosion and sedimentation requires a thorough understanding of sediment sources and factors that drive soil movement in the watershed. This paper describes a study of medium-term water-driven soil erosion rates in a mountainous watershed of the Shihmen Reservoir in Taiwan. A total of 60 sampling sites were selected along a hillslope. At each sampling site, the inventory 137Cs activity was determined and then calculated with the diffusion and migration model to derive soil erosion rates. The rates are one to two orders of magnitude lower than estimates using the Universal Soil Loss Equation, a soil erosion model often used in Taiwan. Results of multiple regression analysis indicate that the spatial variability of soil erosion rates is associated with the relative position of a sampling site to the nearest ridge and soil bulk densities (r 2 = 0.33, p < 0.01). Finally, the patterns of soil redistribution rates on the hillslope follow the 137Cs hillslope model as soil erosion increases in the downslope direction. No deposition site is found at footslope because soil deposition is swept away by regular flooding along the stream channel. This study is an important first step in using 137Cs as a tracer of soil redistribution in mountainous watersheds of Taiwan.

Production of synthetic lightweight aggregate using reservoir sediments for concrete and masonry

The paper reports the investigation of rotary kiln manufactured lightweight aggregates (LWA) using fine sediment deposits dredged from the Shihmen Reservoir in Taiwan. The physical and mechanical properties of the sedimentary, synthetic LWA were assessed as well as the engineering properties of the lightweight aggregate concrete (LWAC) made from the LWA. The physical properties of the concrete masonry units (CMU) made from the LWA were then measured. The investigation revealed the sediments contain all the necessary elements to enable the bloating and calcining processes within the commercial kiln. When exposed to the high heat of the kiln, the extruded sedimentary material undergoes dramatic changes, developing a hard ceramic shell and a porous core comprised of non-interconnected capillaries. The particle densities of the synthetic LWA produced from the kilning process range from 1010 to 1380 kg/m3. LWAC designs using the synthetic LWA produce compressive strengths comparable to normal density concretes and were 29–35% lighter. The test strengths and densities of the LWAC satisfied the requirements of ACI 318 code for structural lightweight concrete. Additionally, sedimentary LWA could be incorporated in automated production facilities to produce high performance CMUs complying with the requirements of the Chinese National Standards (CNS).

Characteristics of sedimentary polycyclic aromatic hydrocarbons (PAHs) in the subtropical Feitsui Reservoir, Taiwan

Polycyclic aromatic hydrocarbons (PAHs) are usually loaded through atmospheric deposition into a water body and eventually into sediments. We study the PAHs from a 22-cm sediment core collected from the subtropical Feitsui Reservoir in Taiwan, and find the PAHs deposition characteristics in the reservoir, the man-made water body, is different from those in natural water bodies. The surficial sedimentary PAH fluxes are significantly higher than those in the European high altitude mountain lakes and those in the northeastern USA urban/industrial lakes. However, the catchment-corrected PAH fluxes normalized by the ratios of the catchment area to the water surface area are comparable to those of remote lakes in Europe and USA, suggesting the sedimentary PAHs in the reservoir is fluvial dominated, i.e., the reservoir system concentrated the atmospheric PAHs from the catchment area into the sediments. PAHs distribution found in the Feitsui Reservoir indicates both biogenic and anthropogenic origins. We also find the vehicular transport upstream of the reservoir is likely one of the PAHs sources to this reservoir.

Comparison of potential water supply and demand in Taiwan

The authors estimated the potential water supply in Taiwan based on hydrologic and water resource data sets pertaining to 233 rainfall stations, 145 stage stations and 109 reservoirs. The comparison between potential water supply estimates and predicted water demand indicated a slight water shortage, even though Taiwan normally receives a large amount of rainfall. This predicted water shortage likely occurred due to the uneven distribution of rainfall in Taiwan. Taken together, the results of this study demonstrate the importance of conservation of forests and paddy fields for the maintenance of base flow and effective management of reservoirs in Taiwan.

Shear Behavior of Reinforced Concrete Beams Made with Sedimentary Lightweight Aggregate without Shear Reinforcement

In this study an experimental investigation on shear behaviors of longitudinally reinforced lightweight aggregate concrete (LWC) beams made with sedimentary lightweight aggregate (LWA) without shear reinforcement was carried out and compared with companion normal-weight concrete (NWC) beams. The sedimentary LWA was a product of fine sediments excavated from the bottom of the Shih-Men Reservoir in Taiwan through proper air drying and sintering processes. A total of 24 simply supported beams were designed for shear failure with a two-point bending system. The primary variables of the investigation include concrete compressive strengths of 23, 43, and 53 MPa and ratios of shear span (a) to effective depth (d), a/d, of 1.5, 2.0, 2.5, and 3.0. The measured shear strengths at failures for all tested beams were recorded and carefully compared against each other. In addition, to assess the validity of the obtained test data, the test results were also compared with those obtained using the present ACI 318 Code equations and Rebeiz's equations for shear strength. The comparisons demonstrate that the obtained shear strengths of LWC and NWC beams are within an acceptable range of the ACI Code. This investigation concludes that sedimentary LWA is recommendable for structural concrete applications.

Identification of physical parameters controlling the dominance of algal species in a subtropical reservoir

Eutrophication is a serious problem of water resource management in Taiwan. The occurrence of annoying algal species as well as abnormally abundant algal mass threatens the quality of water supply. The growth and decline of a specific phytoplankton species are affected by environmental factors, including light, nutrients, temperature, etc. There have been many investigations on the effects of individual factors on the abundance and composition of algal populations. However, many analyses on the effects of environmental factors, especially the concentration of nutrients, on phytoplankton failed to identify the controlling factors on the dynamic change of the phytoplankton species. This study used statistical methods to isolate the effect of seasons on the phytoplankton growth and searched for the relationships between the nutrient concentrations and the abundance of different algal species in Feitsui Reservoir based on the data obtained from 1995 to 2003. We found that the dynamic change of dominance of some species of phytoplankton was strongly related to the seasonal factors. The controlling factors of the survival of an algal species were the settling and mobility of the phytoplankton, the mixing depth and the vertical mixing strength of the water bodies. According to our preliminary findings, the influence of physical factors, varying seasonally, outweighs the influence of nutrients on the algal species composition in Feitsui Reservoir in Taiwan.