Hydraulic model calibration for extreme floods in bedrock‐confined channels: case study from northern Thailand

Palaeoflood reconstructions based on stage evidence are typically conducted in data‐poor field settings. Few opportunities exist to calibrate the hydraulic models used to estimate discharge from this evidence. Consequently, an important hydraulic model parameter, the roughness coefficient (e.g. Manning's n), is typically estimated by a range of approximate techniques, such as ‘visual estimation’ and semi‐empirical equations. These techniques contribute uncertainty to resulting discharge estimates, especially where the study reach exhibits sensitivity in the discharge–Manning's n relation. We study this uncertainty within a hydraulic model for a large flood of known discharge on the Mae Chaem River, northern Thailand. Comparison of the ‘calibrated’ Manning's n with that obtained from semi‐empirical equations indicates that these underestimate roughness. Substantial roughness elements in the extra‐channel zone, inundated during large events, contribute significant additional sources of flow resistance that are captured neither by the semi‐empirical equations, nor by existing models predicting stage–roughness variations. This bedrock channel exhibits a complex discharge–Manning's n relation, and reliable estimates of the former are dependent upon realistic assignment of the latter. Our study demonstrates that a large recent flood can provide a valuable opportunity to constrain this parameter, and this is illustrated when we model a palaeoflood event in the same reach, and subsequently examine the magnitude–return period consequences of discharge uncertainty within a flood frequency analysis, which contributes its own source of uncertainty. Copyright © 2005 John Wiley & Sons, Ltd.     

WATER RESOURCES OF THE CHUNCHUCMIL MAYA*

ABSTRACT. Chunchucmil, on the Yucatán Peninsula, was densely populated in the Maya Late Classic period (ca. a.d. 550–830), even though it depends principally on groundwater. In the 1990s, hydrologic investigations were conducted to determine whether groundwater could have met domestic and agricultural needs. The region's groundwater is near the surface and is influenced by sea‐level fluctuations; however, geochemical analysis revealed that groundwater quality is not affected by mixing with seawater. The potential exists for high and spatially extensive nitrate contamination in this karstic area, yet water‐quality analyses revealed only moderate levels of nitrate in the groundwater. Agricultural limitations are imposed by chloride, total dissolved solids, and salinity, as indicated by electrical conductivity; domestic water use is limited by the presence of nitrate, sulfate, and chloride. Throughflow in the ring of cenotes (sinkholes) around the Chicxulub impact crater may explain the movement and spatial distribution of water‐quality constituents in Chunchucmil's groundwater.     

半干旱半湿润地区洪水预报模型适用性研究

针对半干旱半湿润地区的流域特性和产汇流特点,比较了河北雨洪模型和新安江模型的模型原理和模型特性,以滦河支流老牛河流域为例,开展了洪水预报适用性研究。结果表明,河北雨洪模型的预报精度较高,更适用于半干旱半湿润地区的洪水预报。     

安庆沿江湖泊湿地生态系统服务功能价值评估

安庆沿江湖泊湿地是长江中下游淡水湿地的重要组成部分,是“东亚-澳大利亚鹆鹬类保护网络”中的重要一环,湿地资源十分丰富。本文运用生态经济学中的市场价值法、碳税法、影子工程法等评价方法,依据安庆沿江湖泊湿地特点对它的经济功能价值包括水资源价值、渔业资源价值、土地资源价值等;环境功能价值包括科考旅游价值、涵养水源价值、调节气...     

Geochemistry of the volcano-hydrothermal system of El Chichón Volcano, Chiapas, Mexico

 The 1982 eruption of El Chichón volcano ejected more than 1 km³ of anhydrite-bearing trachyandesite pyroclastic material to form a new 1-km-wide and 300-m-deep crater and uncovered the upper 500 m of an active volcano-hydrothermal system. Instead of the weak boiling-point temperature fumaroles of the former lava dome, a vigorously boiling crater spring now discharges  / 20 kg/s of Cl-rich (∼15 000 mg/kg) and sulphur-poor ( / 200 mg/kg of SO₄), almost neutral (pH up to 6.7) water with an isotopic composition close to that of subduction-type magmatic water (δD=–15‰, δ¹⁸O=+6.5‰). This spring, as well as numerous Cl-free boiling springs discharging a mixture of meteoric water with fumarolic condensates, feed the crater lake, which, compared with values in 1983, is now much more diluted (∼3000 mg/kg of Cl vs 24 030 mg/kg), less acidic (pH=2.6 vs 0.56) and contains much lower amounts of S ( / 200 mg/kg of SO₄, vs 3550 mg/kg) with δ³⁴S=0.5–4.2‰ (+17‰ in 1983). Agua Caliente thermal waters, on the southeast slope of the volcano, have an outflow rate of approximately 100 kg/s of 71  °C Na–Ca–Cl water and are five times more concentrated than before the eruption (B. R. Molina, unpublished data). Relative N₂, Ar and He gas concentrations suggest extensional tectonics for the El Chichón volcanic centre. The ³He/⁴He and ⁴He/²⁰Ne ratios in gases from the crater fumaroles (7.3R_a, 2560) and Agua Caliente hot springs (5.3R_a, 44) indicate a strong magmatic contribution. However, relative concentrations of reactive species are typical of equilibrium in a two-phase boiling aquifer. Sulphur and C isotopic data indicate highly reducing conditions within the system, probably associated with the presence of buried vegetation resulting from the 1982 eruption. All Cl-rich waters at El Chichón have a common source. This water has the appearence of a "partially matured" magmatic fluid: condensed magmatic vapour neutralized by interaction with fresh volcaniclastic deposits and depleted in S due to anhydrite precipitation. Shallow ground waters emerging around the volcano from the thick cover of fresh pumice deposits (Red waters) are Ca–SO₄–rich and have a negative oxygen isotopic shift, probably due to ongoing formation of clay at low temperatures. Received: 21 July 1997 / Accepted: 4 December 1997     

Seasonal dynamics of ciliated protozoa and their potential food in an eutrophic estuary (Bay of Biscay)

Ciliate assemblages, together with phytoplankton and heterotrophic nanoflagellates (HNF) as their potential food, have been surveyed monthly along the salinity gradient of the Nervión River estuary from March 2000 to March 2002. A total of 135 taxa of ciliate have been identified corresponding to 20 orders. Scuticociliates, naked choreotrichs and oligotrichs were the most abundant groups, distributed throughout a broad range of salinity. In addition to these groups, which were the dominant taxa in the middle estuary, tintinnids were characteristic of the ciliate assemblages of the outer estuary whereas in the innermost part naked choreotrichs and oligotrichs decreased in number, being substituted by sessilids, hymenostomatids, peniculids and cyrtophorids. Total ciliate concentrations were among the highest reported in the literature for other estuaries and coastal waters, frequently reaching 10⁵ cells l⁻¹. Meanwhile, tintinnid concentrations were comparable with those of other estuarine and coastal waters. Based on a principal component analysis (PCA) three main groups were delineated, with ciliates and their potential food sources as variables. One was that constituted by freshwater ciliate such as sessilids, hymenostomatids, cyrtophorids and pleurostomatids, which appear in low numbers in the innermost part, mainly in winter. Another group contained diatoms, chlorophytes, flagellates, euplotids and scuticociliates, all of them broadly distributed along the estuary and reaching their maximum density in late spring–summer. The third group was made up of taxa mainly appearing at the seaward end such as dinoflagellates, cyanobacteria, haptorids, tintinnids, naked choreotrichs and oligotrichs, which reached the highest densities in summer and early autumn. Ciliates do not seem to be food limited in the Nervión River estuary or much controlled by metazoan grazing.     

黄河三角洲埕岛近岸海域悬浮泥沙运动

根据1998年9月8日和1999年3月19日两次对埕北海域进行的10个站位的同步海流、悬浮泥沙观测资料，进行该海区的悬浮泥沙输运趋势分析，发现该海区含沙量较大。从整个海区来看，底层含沙量大于表层含沙量，该海区泥沙含量普遍表现为东南部的泥沙含量高于西北部的泥沙含量；由单宽输沙量的计算及有关资料分析可以得出，秋季泥沙运移趋势是由东南向到西北向，而春季泥沙的运移趋势是由东北向到西南向；含沙量是随流速的加大而增加，含沙量的峰值稍滞后于流速的峰值；该海区为冲蚀海区，悬浮泥沙产生的平均年7中刷量为2cm／a，在本海区的地形塑造中占次要地位。     

A new species of the genus Paramisophria (Copepoda, Calanoida,Arietellidae) from the China Seas

ＡｎｅｗｓｐｅｃｉｅｓｏｆｔｈｅｇｅｎｕｓＰａｒａｍｉｓｏｐｈｒｉａ（Ｃｏｐｅｐｏｄａ，Ｃａｌａｎｏｉｄａ，Ａｒｉｅｔｅｌｌｉｄａｅ）ｆｒｏｍｔｈｅＣｈｉｎａＳｅａｓ￥ＬｉａｎＧｕａｎｇｓｈａｎａｎｄＱｉａｎＨｏｎｇｌｉｎ（ＲｅｃｅｉｖｅｄＦｅｂｒｕ...