Experiments on Channel Evolution due to Dam Removal in Taiwan

Due to safety concerns and habitat restoration for landlocked salmon,a 13-m high check dam on Chijiawan Creek was removed in late May 2011 in Taiwan.We conducted experiments to understand channel evolution of different scenarios.We further compared our experimental results of riverbed elevation changes with the analytical solutions derived from the diffusion equation and field dynamics as well after the creek experienced the first flood event.The results indicated that magnitude of discharges and notch size are dominant factors in resulting channel evolution.While the largest differences between grain size distribution are associated with discharge,the largest differences in net change in upstream volume are associated with notch size.While the theoretical equation could help understand the channel change after dam removal,it only explained the evolution closer to the dam.The physical experiments,on the other hand,provided insights especially with regard to comparing alternative proposed management actions.The discrepancies between predicted and actual outcome highlight more needed inputs for future dam-removal assessments.

Genesis, evolution and reservoir identification of a Neogene submarine channel in the southwestern Qiongdongnan Basin, South China Sea

A rarely reported middle-late Miocene-Pliocene channel(incised valley fill),the Huaguang Channel(HGC),has been found in the deep-water area of the southwestern Qiongdongnan Basin(QDNB).This channel is almost perpendicular to the orientation of another well-known,large,and nearly coeval submarine channel in this area.Based on the interpretation of high-resolution 3D seismic data,this study describes and analyzes the stratigraphy,tectonics,sedimentation,morphology,structure and evolution of HGC by means of well-seismic synthetic calibration,one-and two-dimensional forward modeling,attribute interpretation,tectonic interpretation,and gas detection.The HGC is located on the downthrown side of an earlier activated normal fault and grew northwestward along the fault strike.The channel is part of a slope that extends from the western Huaguang Sag to the eastern Beijiao Uplift.The HGC underwent four developmental stages:the(1)incubation(late Sanya Formation,20.4–15.5 Ma),(2)embryonic(Meishan Formation,15.5–10.5 Ma),(3)peak(Huangliu Formation,10.5–5.5 Ma)and(4)decline(Yinggehai Formation,5.5–1.9 Ma)stages.The channel sandstones have a provenance from the southern Yongle Uplift and filled the channel via multistage vertical amalgamation and lateral migration.The channel extended 42.5 km in an approximately straight pattern in the peak stage.At 10.5 Ma,sea level fell relative to its lowest level,and three oblique progradation turbidite sand bodies filled the channel from south to north.A channel sandstone isopach map demonstrated a narrow distribution in the early stages and a fan-shaped distribution in the late stage.The formation and evolution of the HGC were controlled mainly by background tectonics,fault strike,relative sea level change,and mass supply from the Yongle Uplift.The HGC sandstone reservoir is near the Huaguangjiao Sag,where hydrocarbons were generated.Channel-bounding faults and underlying faults link the source rock with the reservoir.A regionally extensive mudstone caprock overlies the channel sandstone.Two traps likely containing gas were recognized in a structural high upstream of the channel from seismic attenuation anomalies.The HGC will likely become an important oil and gas accumulation setting in the QDNB deep-water area.

Downstream Channel Evolution and Its Causes in the Yuan River during the Qing Dynasty

The determination of channel evolutions and the causes is important for reconstructing the evolutionary history of river landforms.This study aimed to elucidate the downstream channel evolution of the Yuan River in Hunan Province,China,during the Qing Dynasty via Landsat 8 satellite image data and relevant literature.The objective was to establish the modes of channel evolution and discuss the significance of historical climate change.The downstream paleochannel of the Yuan River was identified in the Late Ming Dynasty and Early Qing Dynasty(1600–1644 AD),the Kangxi-Qianlong periods of the Qing Dynasty(1661–1796 AD),the Late Qing Dynasty(1840–1912 AD),and the World War II(1939–1945 AD),and three main modes of river evolution were determined.Using remote sensing data and the ancient literature,the evolution characteristics of the paleochannel in the Lower Yuan River were analyzed and its distribution across historical periods was comprehensively revealed.The findings reveal a strong correlation between channel evolution,flood events,and climate change.Numerous flood events that occurred from the Late Qing Dynasty to the World War II caused a high rate of channel evolution,demonstrating the combined effects of climate change and human activities.These findings will help adopt robust and resilient hydrological management methods in the future of a changing climate.

Channel evolution under changing hydrological regimes in anabranching reaches downstream of the Three Gorges Dam

Elucidating the influence of dams on fluvial processes can benefit river protection and basin management. Based on hydrological and topographical data, we analyzed channel evolution in anabranching reaches under changing hydrological regimes influenced by the Three Gorges Dam. The main conclusions are as follows： 1） the channels of specific anabranching reaches were defined as flood trend channels or low-flow trend channels according to the distribution of their flow characteristics. The anabranching reaches were classified as T1 or T2. The former is characterized by the correspondence between the flood trend and branch channels, and the latter is characterized by the correspondence between the flood trend and main channels; 2） on the basis of the new classification, the discrepant patterns of channel evolution seen in anabranching reaches were unified into a pattem that showed flood trend channels shrinking and low-flow trend channels expanding; 3） flood abatement and the increased duration of moderate flow discharges are the main factors that affect channel adjustments in anabranching reaches after dam construction; and 4） in the next few decades, the pattern of channel evolution will remain the same as that of the Three Gorges Dam operation. That is, the morphology will fully adapt to a flow with a low coefficient of variation. Our results are of interest in the management of the Yangtze River and other rivers influenced by dams.

Triple-Polarized Multi-User Mimo-Idma System under Correlated Fading Channel

A multiple-input multiple-output interleave division multiple access (MIMO-IDMA) system with Triple Polarized Division Multiplexing (TPDM) is presented in this paper. The present methodology replaces three independent linearly polarized antennas with a single triple polarized antenna at both the transmitter and receiver. The users in the communication link are accommodated and separated using a user-specific interleaver combined with low rate spreading sequence. To eliminate the effects of multi-stream interference (MSI), minimum mean square error (MMSE) algorithm based on successive interference cancellation (SIC) Multi-user detection (MUD) technique is employed at the receiver. Furthermore, log-maximum a posteriori probability (MAPP) decoding algorithm is implemented at the mobile stations (MSs) to overcome the effects of multi-user interference (MUI) effects. The paper also evaluates the effects of coded MIMO-IDMA in the downlink communication by adopting the Stanford University Interim (SUI) and Long-term Evolution (LTE)channel model specifications. In comparison with the traditional uncoded system, the present solution considering turbo coded triple-polarized MIMO-IDMA system with iterative decoding algorithm provides better bit error rate (BER) with reduced signal to noise ratio (SNR). The simulation results also show that though the SNR requirement is higher for the proposed technique compared to the conventional uni-polarized antenna based MIMO-IDMA system, it gives the advantages of achieving higher data rate with reduced cost and space requirements in the context of a downlink (DL).

Prediction of recent bank retreat processes at typical sections in the Jingjiang Reach

The Jingjiang Reach is experiencing continuous channel degradation owing to operation of the Three Gorges Project （TGP） in 2003. Significant retreat processes at composite riverbanks have occurred at local sites of this reach, which may influence the stability of the fiver regime and the effect of existing river training works. Therefore, bank retreat plays a key role in fluvial processes of the Jingjiang Reach, and it is necessary to predict the long-term processes of bank retreat at typical sections in the reach. In this study, various factors influencing bank retreat in the Jingjiang Reach are investigated, based on bank erosion processes at four sections and the corresponding flow and sediment conditions. It is discovered that fluvial erosion intensity is a dominant factor in controlling the processes of bank retreat in the reach, although other factors, such as bank soil properties, can also influence bank retreat. The bankfull width at a section with severe bank erosion since 2002 is defined as being equal to the sum of the bankfull width in 2002 and the accumulated bank retreat distance after 2002. The magnitude of the bankfull width can be expressed as an exponential function of the previous 5-year average fluvial erosion intensity during flood seasons. The accumulated distances of bank retreat at four sections over the period 2002-2012 are predicted using the proposed empirical relationships, with the calculated bank retreat processes agreeing well with observed data.