• 대한토목학회논문집
• /
• 제40권6호
• /
• pp.555-561
• /
• 2020

본 연구에서는 상, 하부 2개의 대수층이 연결된 누수대수층에 대해 상부 1층 지하수 양수로 인한 하천수 감소량을 산정하기 위해 개발된 Hunt 해석해의 적용성을 평가하였다. 두 대수층의 투수량계수 및 저류계수, 층간 누수계수, 하천-관정 이격거리, 하상의 수리전도도, 하폭 등 다양한 수리특성치 크기 조합에 따라 양수 후 5년 평균 하천수 감소량을 해석해로 산정하고, 범용적으로 사용되고 있는 MODFLOW 지하수유동모형으로 정교하게 모의된 수치해와의 비교를 통해 하폭을 점으로 간주하여 유도한 해석해 적용 결과가 정확한지를 평가하였다. 그 결과 하천-관정 이격거리가 하폭 이상되거나, 하천고갈인자(Stream Depletion Factor)가 약 3,000일 이어야 해석해로 산정한 하천수 감소비의 오차를 0.05 아래로 줄일 수 있는 것으로 분석되었다. 또한 하상수리전도성이 1 m/d 보다 작거나, 하부대수층의 수리확산계수가 100 ㎡/d 보다 작거나, 상부와 하부대수층의 수리확산계수비가 5 이상, 층간 누수계수가 0.0004 m/d 보다 작을 때 해석해가 수치해에 비해 전반적으로 과다하게 산정되는 것으로 분석되었다.

• 한국산림과학회지
• /
• 제112권3호
• /
• pp.374-381
• /
• 2023

산지하천에서 발생하는 돌발홍수는 특정 지점의 점(Point) 유속보다는 전체 구간의 평균 유속에 따라 이동속도가 결정되며, 구간 평균유속은 하천경사, 하상재료, 수리적 거칠기에 많은 영향을 받는다. 이 연구에서는 하천경사 및 거칠기 높이를 이용하여 산지하천의 구간 평균유속 추정방법을 개발하였다. 염료추적자법(Dye Tracing)을 이용하여 특정 구간의 평균유속을 측정하고, LiDAR 영상으로부터 하천 지형 및 형상을 추출하였다. 거칠기 높이를 산정하기 위해 표면 거칠기 변수(R_a, R_max, R_z )와 하상재료의 크기(D₅₀, D₈₄)를 이용하였다. 현장 계측자료로부터 무차원 접근법을 이용하여 구간 평균유속과 유량과의 관계식 v = 0.5499Q^0.6165 을 도출하였으며, R² =0.77의 설명력을 나타냈다. 이 연구에 이용된 5개의 거칠기 높이 중 평균 거칠기 높이(R_a)의 RMSE가 0.45로서 다른 거칠기 높이의 범위(0.47-1.04)보다 낮게 나타나 평균 거칠기 높이(R_a)가 구간 평균유속 산정을 위한 거칠기 높이 인자로 가장 적합하다고 판단되었다.

• Journal of Ecology and Environment
• /
• 제47권4호
• /
• pp.200-210
• /
• 2023

Background: Cambaroides similis is an endangered candidate species living in the stream of South Korea. Freshwater crayfish is known to decline rapidly not only domestically, but also internationally. Its decline is projected to be further exacerbated due to climate change. Understanding physical characteristics of the habitat is crucial for the conservation of an organism. However, comprehensive data regarding the distribution and physical habitat characteristics of C. similis are currently unavailable in South Korea. Thus, the objective of this study was to ascertain preferred ranges for water depth, current velocity, and streambed substrate of C. similis using Weibull model. Results: In this study, C. similis was found at 59 sites across 12 regions in South Korea. Its optimal water depth preferences ranged from 11.9 cm to 30.1 cm. Its current velocity preferences ranged from 9.8 cm s^-1 to 29.1 cm s^-1. Its substrate preferences ranged from -5.1 𝜱_m to -2.5 𝜱_m. Median values of central tendency were determined as follows: water depth of 21.4 cm, current velocity of 21.2 cm s^-1, and substrate of -4.1 𝜱_m. Mean values of central tendency were determined as follows: water depth of 21.8 cm, current velocity of 22.0 cm s^-1, and substrate of -4.4 𝜱_m. Mode values of central tendency were determined as follows: water depth of 21.7 cm, current velocity of 20.1 cm s^-1, and substrate of -3.7 𝜱_m. Conclusions: Based on habitat suitability analysis, physical microhabitat characteristics of C. similis within a stream were identified as Run section with coarse particle substrate, low water depth, and slow current velocity. Due to high sensitivity of these habitats to environmental changes, prioritized selection and assessment of threats should be carried out as a primary step.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2004년도 춘계학술발표회
• /
• pp.517-524
• /
• 2004

The leading cause of bridge failures is scouring bed material from around bridge foundations. Many advanced countries such as U.S.A., U.K., the Netherlands and New Zealand have developed and revised their own bridge scour manuals fit for their field conditions. In Korea, researches for reducing bridge failures during floods have concentrated on analysis, laboratory test and countermeasure of bridge scour during the last ten years. however no comprehensive manual for evaluating bridge scour and for identifying the conditions of bridge foundations has been provided yet. In this study, a new bridge scour manual is developed for the accurate evaluation of bridge scour, which reflects domestic field conditions with various streambed materials. The SRICOS method and the Erodibility Index Method are suggested for fine-grained soils and weathered rocks, respectively. In addition, bridge scour analysis algorithms are developed for field engineers to estimate bridge scour depth and to evaluate the susceptibility of bridge scour with ease.

• 생태와환경
• /
• 제41권2호
• /
• pp.137-143
• /
• 2008

The abundance and community structure of epilithic diatoms grown on different substrata were investigated in two first-order streams located in a limestone and granite area, north of the Suzuka Mountains in Central Japan. Experiments were conducted as follows: limestone and granite without algae were submerged in their own streambed or another stream station and incubated for seven weeks, while limestone and granite with algae were transferred to another stream station and incubated at the same time. The diatom biomass was consistently high in the lime-stone station experiments compared to those at the granite station. In addition, there was more diatom biomass on granite substrata than on the limestone substrata at both stations. The present results suggested that the difference in water chemistry including the major nutrient concentrations was the limiting factor for algal growth in these two streams; however, when the water chemistry was the same in each stream, the difference in substratum characteristics became the important factor affecting the diatom abundance. The diatom community grown on the transferred substrata with and without algae became similar to those grown on the original substrata in each stream during the incubation period. It was suggested that the effect of the substrata characteristics on the diatom community structure was rather small.

• 한국지반공학회논문집
• /
• 제20권3호
• /
• pp.67-74
• /
• 2004

사례 연구를 통해서 실제 세립토 교량현장에 대해 기존 교량세굴 해석모델들의 적용성을 분석하였다. 하상이 실트질 점토로 구성된 강화 초지대교를 대상교량으로 선정하여 현장조사를 실시하였다. 초음파 센서장비를 이용하여 교각주변의 세굴심을 직접 측정하였으며, 불교란시료를 채취하여 지반공학적 특성을 결정하고, 또한 세굴률 실험을 통해 대상 지반의 유속별 세굴률을 분석하였다. 그 결과를 바탕으로 기존에 제안된 대표적인 교량세굴 해석모델들을 이용하여 주요 교각의 세굴심을 예측하여 실측 세굴심과 비교하였다. 지반의 침식특성을 고려하지 않는 기존의 교량세굴 해석모델들은 모두 3.6∼6.5의 비율로 세굴심을 과대평가하는 경향을 보였으며, SRICOS 방법은 실측세굴심에 비해 1.7배의 합리적인 결과를 보여주었다.

• 한국환경과학회지
• /
• 제14권8호
• /
• pp.739-748
• /
• 2005

The purpose of this study is to analyze seasonal changes in structure and landscape of Gongji stream corridor in Chuncheon, and to suggest some guidelines to contribute to creating a desirable close-to- nature stream. The study seasonally surveyed floodplain and revetment conditions, channel micro-topography, streamflow level and velocity, and vegetational cover. Flooding, water level, and vegetation were major factors of affecting seasonal changes in streambed structure and stream landscape. Small sand bars and islands were considerably disturbed by flooding and water level change. However, large islands and sand bars in the upper and middle section of the study stream remained or reappeared even after flooding. Flooding also tended to repeat channel sedimentation at the same spot. Controlling water volume of the Euiam Lake, which is adjacent to the study stream, caused higher water level downstream in the dry seasons. The majority of vegetation in sand bars and islands was washed away by the floods. Vehicle passing, crop cultivation, and ball game were other elements which disturbed vegetation in the floodplain. Creating a close-to-nature stream should reflect micro-topographical changes of channel by flooding, prevent improper vehicle entry and human use, and remove concrete material in the revetment and floodplain.

• 한국수자원학회:학술대회논문집
• /
• 한국수자원학회 2018년도 학술발표회
• /
• pp.295-295
• /
• 2018

본 연구는 보 상류 하상경사 변화에 따른 보 하류부의 세굴 문제점 개선을 위해 하상경사에 대한 세굴영향을 분석하기 위한 실험연구이다. 세굴실험은 상류 하상경사 변화에 대해 보 하류부의 세굴변화를 중심으로 세굴영향을 검토하였다. 본 실험은 상류 하상경사 변화에 대한 세굴영향을 분석하기 위한 것으로 총 6개 하상경사에 대해 국부세굴 및 퇴적경향을 비교분석하였다. 보의 높이 및 물받이 길이는 0.3 m로 설치하였고, 실험 단위폭당 유량은 $0.117m^3/s/m$로 모든 케이스에 동일하게 적용하여 수행하였다. 보를 통과하는 고속사류로 인한 국부세굴의 영향분석을 위해 광대역 레이저 스캐너(RIEGL LMS-Z390)를 이용하여 세 퇴적량을 측정 및 분석하였다. 연구결과, 상류 하상경사 변화에 따른 보 하류부 세굴 특성 분석 결과 상류부의 하상경사가 급해질수록 세굴길이 및 세굴심도의 값은 크게 변화하는 것을 확인하였다. 이는 하상경사 변화에 따라 수류의 총에너지 경사가 급하게 변화하게 되고 따라서 보 하류부의 소류력 증가에 기인한 것으로 판단된다.

• Structural Monitoring and Maintenance
• /
• 제2권2호
• /
• pp.145-164
• /
• 2015

Bridge scour is the predominant cause of overwater bridge failures in North America and around the world. Several sensing systems have been developed over the years to detect the extent of scour so that preventative actions can be performed in a timely manner. These sensing systems have drawbacks, such as signal inaccuracy and discontinuity, installation difficulty, and high cost. Therefore, attempts to develop more efficient monitoring schemes continue. In this study, the viability of using optical dissolved oxygen (DO) probes for monitoring scour depths was explored. DO levels are very low in streambed sediments, as compared to the standard level of oxygen in flowing water. Therefore, scour depths can be determined by installing sensors to monitor DO levels at various depths along the buried length of a bridge pier or abutment. The measured DO is negligible when a sensor is buried but would increase significantly once scour occurs and exposes the sensor to flowing water. A set of experiments was conducted in which four dissolved oxygen probes were embedded at different soil depths in the vicinity of a mock bridge pier inside a laboratory flume simulating scour conditions. The results confirmed that DO levels jumped drastically when sensors became exposed during scour hole evolution, thereby providing discrete measurements of the maximum scour depth. Moreover, the DO probes could detect any subsequent refilling of the scour hole through the deposition of sediments. The effect of soil permeability on the sensing response time was also investigated.

• Structural Monitoring and Maintenance
• /
• 제1권2호
• /
• pp.183-195
• /
• 2014

Scour is one of the leading causes of overwater bridge failures worldwide. While monitoring systems have already been implemented or are still being developed, they suffer from limitations such as high costs, inaccuracies, and low reliability, among others. Also, most sensors only measure scour depth at one location and near the pier. Thus, the objective is to design a simple, low cost, scour hole topography monitoring system that could better characterize the entire depth, shape, and size of bridge scour holes. The design is based on burying a robust, waterproofed, piezoelectric sensor strip in the streambed. When scour erodes sediments to expose the sensor, flowing water excites it to cause the generation of time-varying voltage signals. An algorithm then takes the time-domain data and maps it to the frequency-domain for identifying the sensor's resonant frequency, which is used for calculating the exposed sensor length or scour depth. Here, three different sets of tests were conducted to validate this new technique. First, a single sensor was tested in ambient air, and its exposed length was varied. Upon verifying the sensing concept, a waterproofed prototype was buried in soil and tested in a tank filled with water. Sensor performance was characterized as soil was manually eroded away, which simulated various scour depths. The results confirmed that sensor resonant frequencies decreased with increasing scour depths. Finally, a network of 11 sensors was configured to form a distributed monitoring system in the lab. Their exposed lengths were adjusted to simulate scour hole formation and evolution. Results showed promise that the proposed sensing system could be scaled up and used for bridge scour topography monitoring.