Fuzzy Optimization Neural Network Approach for Ice Forecast in the Inner Mongolia Reach of the Yellow River/Approche d'Optimisation Floue de Réseau de Neurones pour la Prévision de la Glace Dans le Tronçon de Mongolie Intérieure du Fleuve Jaune

Abstract

In ice forecasting, a key problem is the forecast of freeze-up and break-up dates. Ice-water mechanics and the principle of heat-exchange were mainly adopted in previous research. However, the mathematical models in these studies are complex and many parameters are required in relation to upstream and/or downstream gauging stations. Moreover, too many assumptions or simplifications for these parameters and constraints directly lead to low accuracy of the models and limitations as to their practical applications. This paper develops a fuzzy optimization neural network approach for the forecast of freeze-up date and break-up date. The Inner Mongolia reach lies in the top north of the Yellow River, China. Almost every year ice floods occur because of its special geographical location, hydrometeorological conditions and river course characteristics. Therefore, it is of particular importance for ice flood prevention to forecast freeze-up date and break-up date accurately. A case study in this region shows that the proposed methodology may allow obtaining useful results.     

海勃湾水库用于黄河内蒙古河段防凌作用的研究

黄河内蒙古河段冰期一般在冬季封河期和春季开河期０容易出现严重凌情,造成灾害。故良好的封河形势和开河形势是避免凌灾发生的重要条件,自１９６８年刘家峡水库运用以来,黄河内下河段凌情已大有缓解。但是,由于有峡水库距黄河内下河段较远。对河道凌情变化反应不够灵敏。因此,一些年份仍有较为严重的凌灾发生。在分析黄河内蒙古河段封、开河形势特点的基础上,深入研究了海勃湾水库用于该段春季防凌调度的作用和能力,为黄河内     

Evolution of cutoffs across meander necks in Powder River,Montana, USA

Over a period of several decades, gullies have been observed in various stages of forming, growing and completing the cutoff of meander necks in Powder River. During one episode of overbank flow, water flowing over the down-stream bank of the neck forms a headcut. The headcut migrates up-valley, forming a gully in its wake, until it has traversed the entire neck, cutting off the meander. The river then follows the course of the gully, which is subsequently enlarged as the river develops its new channel. The complete process usually requires several episodes of high water: in only one of the five cases described herein was a meander cutoff initiated and completed during a single large flood. © 1998 John Wiley & Sons, Ltd.     

Climatic effects on ice phenology and ice-jam flooding of the Athabasca River in western Canada

ABSTRACT

In cold region environments, any alteration in the hydro-climatic regime can have profound impacts on river ice processes. This paper studies the implications of hydro-climatic trends on river ice processes, particularly on the freeze-up and ice-cover breakup along the Athabasca River in Fort McMurray in western Canada, which is an area very prone to ice-jam flooding. Using a stochastic approach in a one-dimensional hydrodynamic river ice model, a relationship between overbank flow and breakup discharge is established. Furthermore, the likelihood of ice-jam flooding in the future (2041–2070 period) is assessed by forcing a hydrological model with meteorological inputs from the Canadian regional climate model driven by two atmospheric–ocean general circulation climate models. Our results show that the probability of ice-jam flooding for the town of Fort McMurray in the future will be lower, but extreme ice-jam flood events are still probable.     

Naturalizing the freezeup regimes of regulated rivers and exploring implications to spring ice-jam flooding

Naturalization of the flow hydrograph and ice regime is a key step in assessment of ecological and socioeconomic impacts of regulation across large portions of Europe, Asia and North America, where many rivers are dammed for hydropower generation. Building on previous naturalization of early-freshet flows that influence the nature of breakup and jamming events, novel methodology is developed to estimate natural freezeup flows and thence determine associated water levels, also known to influence subsequent breakup events. Using reservoir inflows, the new methodology is applied to the lower portion of the regulated Peace River, Canada, which forms the northern boundary of the Peace-Athabasca Delta (PAD), a Ramsar wetland of international importance that partially depends on spring ice-jam flooding for recharge of its high-elevation, or “perched” basins. The PAD provides habitat for numerous aquatic, terrestrial and avian species and is vital to the maintenance of indigenous culture and lifeways. Naturalized freezeup levels in the lower Peace River are shown to be nearly always lower than corresponding regulated values, with the difference averaging ~1.6 m. Consistent with known physics of river ice breakup processes, the present results suggest that ice-jam flood frequency would likely have been greater under natural conditions. Though potentially adverse from the ecological standpoint, reduction of spring ice-jam flooding can benefit riverside communities. Implications of the present results to and comparison with, other Canadian and international rivers are discussed.     

Impacts of future climate on the hydrology of a northern headwaters basin and its implications for a downstream deltaic ecosystem

Anthropogenic and climatic-induced changes to flow regimes pose significant risks to river systems. Northern rivers and their deltas are particularly vulnerable due to the disproportionate warming of the Northern Hemisphere compared with the Southern Hemisphere. Of special interest is the Peace–Athabasca Delta (PAD) in western Canada, a productive deltaic lake and wetland ecosystem, which has been recognized as a Ramsar site. Both climate- and regulation-induced changes to the hydrological regime of the Peace River have raised concerns over the delta's ecological health. With the damming of the headwaters, the role of downstream unregulated tributaries has become more important in maintaining, to a certain degree, a natural flow regime, particularly during open-water conditions. However, their flow contributions to the mainstem river under future climatic conditions remain largely uncertain. In this study, we first evaluated the ability of a land-surface hydrological model to simulate hydro-ecological relevant indicators, highlighting the model's strengths and weaknesses. Then, we investigated the streamflow conditions in the Smoky River, the largest unregulated tributary of the Peace River, in the 2071–2100 versus the 1981–2010 periods. Our modelling results revealed significant changes in the hydrological regime of the Smoky River, such as increased discharge in winter (+190%) and spring (+130%) but reduced summer flows (−33%) in the 2071–2100 period compared with the baseline period, which will have implications for the sustainability of the downstream PAD. In particular, the projected reductions in 30-day and 90-day maximum flows in the Smoky River will affect open-water flooding, which is important in maintaining lake levels and connectivity to perimeter delta wetlands in the Peace sector of the PAD. The evaluation of breakup and freeze-up flows for the 2071–2100 period showed mixed implications for the ice-jam flooding, which is essential for recharging high-elevation deltaic basins. Thus, despite projected increase in annual and spring runoff in the 2071–2100 period from the Smoky sub-basin, the sustainability of the PAD still remains uncertain.     

我国江河工程凌汛计算研究进展综述

冬季,我国北纬30°以北和青藏高原的江河上都存在不同程度冰情,有些江河还会发生较严重凌汛。在这些地区兴建水利水电工程及跨河建筑物,因改变了部分河道热力、动力及边界条件,不仅影响到河道防凌安全,而且往往对工程本身安全构成威胁。50年来,我国的工程凌汛研究工作,在吸取了国外凌汛研究经验基础上,结合工程设计、施工和管理实践,进行了大量资料测验、科学试验及分析研究。通过总结以上研究成果,对工程影响下的3类冰凌洪水形成条件及主要特征量提出了较完整、科学且实用的分析计算方法,以期为兴建同类工程时的凌汛计算提供有益借鉴。