• Korean Journal of Ecology and Environment
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• 제42권4호
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• pp.441-451
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• 2009

The major objectives of this study were to evaluate trophic state of reservoirs using major water quality variables and its relations in terms of trophic guilds and tolerance guilds with dominant lentic fishes. For this study, we selected 6 artificial reservoirs such as Namyang Reservoir ($N_yR$), Youngsan Reservoir ($Y_sR$), Daechung Reservoir ($D_cR$), Chungju Reservoir ($Cj_R$), Chungpyung Reservoir ($C_pR$), and Paldang Reservoir ($P_dR$), and collected fish during 2000~2007 along with data analysis of water quality monitored by the ministry of environment, Korea. Biological oxygen demand (BOD) and chemical oxygen demand (COD), indicators of organic matter pollution, varied depending on types of the reservoirs and the spatial patterns in terms of trophic gradients were similar to patterns of nutrients, Secchi depth and chlorophyll-a. Analysis of trophic state index (TSI) showed that reservoirs of $D_cR$ and $C_jR$ were mesotrophy and other 4 reservoirs were eutrophic state. The relations of trophic relations showedthat TSI (Chl-a) had a positive linear function [TSI (CHL)=0.407 TSI (TP)+28.2, n=138, p<0.05] with TSI (TP) but had a weak relation with TSI (TN). Also, TSI (TP) were negatively correlated ($R^2=0.703$, p<0.05) with TSI (SD), whereas TSI (TN) was not significant (p>0.05) relations with TSI (SD). Tolerance guilds of lentic fishes, based on three types of the reservoirs, reflected the exactly water quality in the TN, TP, BOD, and COD, and similar trends were shown in the fish feeding/trophic guilds.

• Journal of The Korean Society of Agricultural Engineers
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• 제61권5호
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• pp.33-47
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• 2019

The environmental ecological flow (EEF) of stream or river will be designated according to the enforcement of the Water Environment Preservation Act. Previous researches by Ministry of Environment have proposed agricultural reservoirs as alternative resources to secure river flow where multi-purpose dam does not exist. However, agricultural reservoirs are constructed for the supply of agricultural water, and in fact, there is not a sufficient amount of water to be supplied to rivers as EEF. Therefore, this study examines the economic feasibility of securing EEF through the remodeling or construction of agricultural reservoirs. We investigated water balance of reservoir through simulation of three types of water supply demands such as agricultural water, agricultural water and river maintenance flow, and agricultural water and environmental ecology flow. The economics analysis was conducted on water supply demands and corresponding remodeling or construction of reservoirs. As a result, it was found that the method of securing through heightening existing reservoir enhancement is economically feasible. However, it was not possible to secure all the amount of the EEF due to the size limitation of existing reservoirs or constrain of the watershed for newly built reservoir. Therefore, in order to secure all of the EEF, the utilization of other alternatives as well as agricultural reservoirs should be considered. This study demonstrated the method of economical feasibility study of securing river maintenace flow and EEF using agricultural reservoirs and other considerations.

• Journal of Korean Society on Water Environment
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• 제23권4호
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• pp.512-517
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• 2007

The limiting nutrient of eutrophication in freshwater bodies in Korea was examined and the phosphorus concentration standard for sewage treatment effluent was discussed. The weight ratio of N/P in 13 major reservoirs showed the range of 18 to 163, which implies phosphorus is more limited than nitrogen for algal growth. In the correlation analysis phosphorus showed higher correlation with chlorophyll-a concentration than with nitrogen. In the algal bioassay phosphorus spike test enhanced algal growth in all 25 samples of five reservoirs, while nitrogen was found to co-limit only in four samples. It confirms that phosphorus is the only limiting nutrient for eutrophication in Korean reservoirs. As many reservoirs are eutrophic in Korea, phosphorus control is critical for the management of water quality. The phosphorus standard of sewage treatment effluent in Korea was compared with other countries, and it can be concluded that phosphorus standard is too high to be effective in eutrophication control and a lower phosphorus standard is essential for the water quality improvement.

• The Korean Journal of Petroleum Geology
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• 제14권1호
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• pp.36-44
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• 2008

Natural gas in tight reservoirs, one of unconventional hydrocarbon resources, has become a significant exploration and exploitation targets. Tight gas reservoirs are the gas-bearing rocks that commonly have a permeability of less than 0.1 millidarcy (mD). Tight gas reservoirs are characterized by extensive and deep locations as well as abnormal pressure such as over- or under-pressure. The tight gas reservoirs are independent of structural or stratigraphic traps, whereas conventional gases normally occur at these traps. Tight gas reservoirs can be productive when stimulated by hydraulic fracturing. Better production areas within the tight reservoir beds are referred to as sweet spots that are commonly caused by natural fractures, which should be understood and identified to enhance the recovery of the gas from tight reservoirs. The exploration and production techniques allow the commercial production of tight gas, one of environmentally friendly resources. Slant and horizontal wells have best production when they intersect the fractures. Gas production from the tight reservoirs has rapidly grown in U.S. and Canada. Indeed, the U.S. gas production of tight sandstones increases from 11.1% in 1990 to 24.1% in 2005. The presence of tight gas reservoirs has been suggested on the Korean offshore block 6-1. Paradigm shift from conventional to unconventional tight reservoir is required to develop the tight gas from the block.

• Fisheries and Aquatic Sciences
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• 제26권5호
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• pp.305-317
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• 2023

Ethiopia is branded as the Water Tower of Africa because of its abundant inland water bodies that may be used sustainably to boost the economy. This review article's goal is to examine the current status and future potential of Ethiopia's fisheries, with a special focus on reservoirs. There are 200 known fish species (194 native, 40 endemic, and 11 exotic) in in Ethiopia's inland water. Ethiopia's fish production has increased by a factor of more than five in the past three decades (3,500 tons in 1983 to 15,681 tons in 2000 and 18,058 tons in 2010). However, fish produced in reservoirs is too low (8,059 t/year). The current fish harvests from reservoirs are significantly below the predicted potential yield, accounting for only 35% of the calculated fish production capacity. In this review, 14 potential reserves were revealed. A total of 48 fish species have been reported in these, of which 26 species (or around 54%) are present in Alwero reservoir. 19 of the 48 species that have been officially recognized belong to the Cyprinidae family and made up nearly 40% of the fish population in Ethiopian reservoirs. There has been, however, a decline in the productivity of Ethiopia's reservoir fish. Hence, actively start fishing in the numerous reservoirs that have been neglected yet, link the potential of fisheries and the benefits of the fish farming supply chain, let's begin building several other reservoirs similar to the Grand Ethiopian Renaissance Dam and beginning mechanized-based fish harvesting.

• Magazine of the Korean Society of Agricultural Engineers
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• 제30권3호
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• pp.95-105
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• 1988

This study refers to the development of a hydrologic model simulating daily inflow and release rates for irrigation reservoirs. A daily - based model is needed for adequate operation of an irrigation reservoir sufficing the water demand for paddy fields which is closely related to meteorological conditions. And the objective or this study is to develop a Daily Irrigation Reservoir Operation Model(DIROM) combining the inflow and the release models which depicts the daily water level fluctuations of an irrigation reservoir, and to evaluate the applicability of the model. DIROM was applied to four reservoirs and daily water levels were simulated and compared to the observed data. The model behaviour was also compared with that of a ten - day based model, Reservoir Operation Study(ROS) which has been applied for determining the design capacity of reservoirs. Various combinations of measured and simulated inflow and release rates for tested reservoirs were used to define the daily water level fluctuations. Simulated release rates and measured inflow data resulted in larger errors, and simulated inflow and release rates produced the smallest errors in water level comparison. Two resevoir operation models, DIROM and ROS were applied to the same reservoir and the simulation results compared. The computational errors of DIROM ware smaller than those of ROS, and DIROM was more sensitive to meteorological conditions. DIROM demonstrated its potenial applicability in water management and operation.

• Journal of Korean Society on Water Environment
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• 제30권1호
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• pp.31-43
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• 2014

Recently, Andong Reservoir and Imha Reservoir located in Nakdong River basin (Korea) are being connected by a tunnel (length 2km, diameter 5.5m) for a conjunctive use. The objectives of this study were to construct a two dimensional(2D) laterally-averaged model for two reservoirs, and examine the effects of connection on the water transportation and temperature stratification in the reservoirs. The 2D models for each reservoir were calibrated using field data obtained in 2006, and applied to the linked system for the year of 2002 when a severe flood intruded into Imha Reservoir during the typhoon Rusa. Simulation results showed that 364 million $m^3$ of water can be conveyed from Imha to Andong, while 291 million $m^3$ of water from Andong to Imha after connection. It resulted in 1.38 m increase of annual averaged water level in Andong Reservoir, whereas 3.75 m decrease in Imha Reservoir. The structures of thermal stratification in both reservoirs were influenced in line with the flow exchanges. In Andong Reservoir, the location of thermocline moved upward about 10 m compared to an independent operation. The results imply that the persistent turbidity issue of Imha Reservoir might be shifted to Andong Reservoir during a severe flood event after connection.

• Journal of The Korean Society of Agricultural Engineers
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• 제55권3호
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• pp.13-24
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• 2013

Agriculture is affected directly by climate conditions and changes, and it is necessary to understand the impact of climate change on agricultural reservoirs which are the main water resources for paddy fields in Korea. This study aimed to evaluate the impact of climate change on the anti-drought capacity including water supply capability (WSC) and drought response ability (DRA) of agricultural reservoirs based on RCP (Representative Concentration Pathway) 4.5 and 8.5 scenarios of CanESM2 (The Second Generation Earth System Model) provided by CCCma (Canadian Center for Climate Modeling and Analysis). The WSC and DRA were estimated using frequency analysis and runs theory. The six reservoirs (Yooshin, Nogok, Kumsung, Songgok, Gapyung, Seoma) were selected considering geographical characteristics and design criteria of reservoir capacity. In case of Seoma reservoir, more than 10 year drought return period (DRP), the variation of the WSC was estimated larger than the others. In case of Yooshin reservior (2~5 DRP) DRC was decreased in 2025s under RCP8.5. These results could be utilized for agricultural reservoirs management and future design criteria considering climate change impacts on paddy irrigation.

• Korean Journal of Ecology and Environment
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• 제42권4호
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• pp.432-440
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• 2009

During the period of past fifteen years (1992~2006), variations of chlorophyll a in relation with water quality in freshwater reservoirs were investigated. This study compared total nitrogen (TN), total phosphorus (TP), chlorophyll a, Secchi depth (SD) and total suspended solids (TSS) between terrestrial freshwater reservoir and coastal freshwater reservoir systems based on their location. Regression analyses (linear and non-linear regressions) were applied for all study sites to examine relationship and interaction of these factors in the freshwater systems from in-land to coasts. The results demonstrated that chlorophyll a was significantly correlated to total phosphorus ($R^2=0.94$, P<0.0001) and was remarkably related to TSS increase ($R^2=0.63$, P<0.0001) in the selected reservoirs. The TN : TP ratio in the reservoir systems was higher than Redfield ratio (16 : 1) indicating that the reservoirs are potentially experiencing P limitation. Water quality of coastal freshwater reservoir system was more significantly decreased than the reservoirs located in in-land during the past fifteen years. The strict management of nutrient discharge into freshwater systems should implemented in the coastal reservoirs since the freshwater is introduced into coastal estuarine systems.

• Magazine of the Korean Society of Agricultural Engineers
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• 제35권2호
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• pp.65-72
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• 1993

When a drought occurs in an area irrigated by multi-reservoirs, onerating a single reservoir separately to control the reservoir' storage is not a desirable solution. In order to reduce damages effectively for the areal drought, the storage of the reservoirs within the areal boundary should be managed as a group. Storage management procedures are as follows : 1. Collecting and checking the present storages of all reservoirs 2. Computing the drought frequency and depth; and finally, establishing a suitable storage saving strategy based on the estimated drought depth. For the purpose of this storage management, the RESTOMS(Reservoirs Storage Management System) was developed and the system was composed of the PRIME computer and the ORACLE as a distributed database management system, which was the host computer of Rural Development Corporation and would be on-lined with the regional offices throughout the country. Reservoirs operated by Farm Land Improvment Association were comprised in the DB system. Using the RESTOMS, the drought frequencies and drought depths were calculated with respect to the reservoir storage records(1967 to 1992). It was obvious that the results were closely corresponding to the real drought records.