Stormflow generation involving pipe flow in a zero‐order basin of Peninsular Malaysia

Hydrological responses in a zero‐order basin (ZOB), a portion of whose discharge emerged via preferential flow through soil pipes, were examined over a 2‐year period in Peninsular Malaysia to elucidate primary stormflow generation processes. Silicon (Si) and specific conductance (EC) in various runoff components were also measured to identify their sources. ZOB flow response was dependent on antecedent precipitation amount; runoff increased linearly with precipitation during events >20 mm in relatively wet antecedent moisture conditions. Runoff derived from direct precipitation falling onto saturated areas accounted for <0·2% of total ZOB flow volume during the study period, indicating the predominance of subsurface pathways in ZOB flow. ZOB flow (high EC and low Si) was distinct from perennial baseflow via bedrock seepage (low EC and high Si) 5 m downstream of the ZOB outlet. Pipe flow responded quickly to ZOB flow rate and was characterized by a threshold flow capacity unique to each pipe. Piezometric data and pipe flow records demonstrated that pipes located deeper in the soil initiated first, followed by those at shallower depths; initiation of pipe flow corresponded to shallow groundwater rise above the saprolite‐soil interface. Chemical signatures of pipe flow were similar to each other and to the ZOB flow, suggesting that the sources were well‐mixed soil‐derived shallow groundwater. Based upon the volume of pipe flow during storms, the combined contribution of the pipes monitored accounted for 48% of total ZOB flow during the study period. Our results suggest that shallow groundwater, possibly facilitated by preferential flow accreted above the saprolite–soil interface, provides dominant stormflow, and that soil pipes play an important role in the rapid delivery of solute‐rich water to the stream system. Copyright © 2006 John Wiley & Sons, Ltd.     

Water and sediment quality, partial mass budget and effluent N loading in coastal brackishwater shrimp farms in Bangladesh

The present study aimed to quantify the water and sediment quality and growth and production parameters and to establish nutrient budgets for an average of five selected semi-intensive shrimp ponds in Bangladesh over a growing cycle. Physico-chemical parameters of water and sediments were measured and analyzed by standard methods. Gross yield (kg ha-1) of shrimp was calculated from the stocking and harvesting data. Finally, a partial nutrient mass budget for N and P was calculated. Most of the parameters of water and sediments correlated significantly with each other suggesting a high degree of interactions between different parameters in the system. Significantly higher concentrations of all species of nitrogenous nutrients were recorded in the effluent waters than that entering into the ponds. Therefore, a high loading and net output of nitrogenous nutrients in effluent waters was documented. The study also indicated a net discharge of solids and minerals through effluent loading. However, significantly lower concentrations of phosphorus in the effluent water indicated a net retention and trapping of phosphatic nutrients in the environment. Total production ranged between 532.0 and 697.0 kg ha-1 cycle-1 and P. monodon production between 484.0 and 562.0 kg ha-1 cycle-1. Ponds gained nitrogen primarily from intake water (55%) and fertilizers (29%), and nitrogen was lost primarily from water exchange (78%) and harvested shrimp (12%). Phosphorus gain occurred mostly from intake water (52%) and fertilizers (25%), and phosphorus was lost primarily from water exchange (52%) and harvested shrimp (3.3%). About 10% of input nitrogen and 44% of phosphorus were not accounted for in measured losses, and presumably were fixed or metabolized in the system. On average, 78 g N was discharged to and 25 g P was removed from the surrounding water by the system for each kilogram of shrimp produced. Mean conversion of feed nitrogen and phosphorus to shrimp flesh averaged 74% and 40%, respectively. It was concluded that semi-intensive systems serve as net supplier of N to and net remover of P from the surrounding water.     

The design of visco‐acoustic weighted L1‐error frequency–space wavefield extrapolators

Seismic imaging is an important step for imaging the subsurface structures of the Earth. One of the attractive domains for seismic imaging is explicit frequency–space (f – x) prestack depth migration. So far, this domain focused on migrating seismic data in acoustic media, but very little work assumed visco‐acoustic media. In reality, seismic exploration data amplitudes suffer from attenuation. To tackle the problem of attenuation, new operators are required, which compensates for it. We propose the weighted L ₁ ‐error minimisation technique to design visco‐acoustic f – x wavefield extrapolators. The L ₁ ‐error wavenumber responses provide superior extrapolator designs as compared with the previously designed equiripple L ₄ ‐norm and L_∞‐norm extrapolation wavenumber responses. To verify the new compensating designs, prestack depth migration is performed on the challenging Marmousi model dataset. A reference migrated section is obtained using non‐compensating f – x extrapolators on an acoustic dataset. Then, both compensating and non‐compensating extrapolators are applied to a visco‐acoustic dataset, and both migrated sections are then compared. The final images show that the proposed weighted L ₁ ‐error method enhances the resolution and results in practically stable images.     

Porphyry Cu deposits linked to episodic growth of an underlying parental magma chamber

Saindak is one of the typical porphyry Cu deposits (PCDs) in the Chagai magmatic arc in Pakistan. Ore-forming porphyries at Saindak PCD are mainly composed of tonalite. Here, we use geochemistry of apatite enclosed in plagioclase phenocrysts from the ore-forming tonalite to constrain the releasing and recharging processes of S and Cl in the underlying parental magma chamber during PCD mineralization. Although apatite inclusions have homogeneous intra-grain S and Cl compositions, there is significant inter-grain S and Cl variations in apatite inclusions located from core to rim in the hosting plagioclase. Such inter-grain S and Cl variation in apatites are coupled with the core-to-rim trends of An, FeO and Mg contents of the hosting plagioclase phenocryst. It indicates that the Saindak PCD likely formed by episodic injection of primitive magmas during the growth of an underlying magma chamber, rather than by one major injection or by addition of mafic melt derived from different source region. Each primitive melt injection introduced essential ore-forming materials such as S and Cl, which were rapidly and effectively released to the coexisting fluids, causing mineralization. Once primitive melt injection stops, signaling the end of growth of underlying magma chamber, mineralization will cease quickly although the hydrothermal system can still survive for a long time. However, the later released fluids are relatively depleted in ore-forming materials, and thus have lower capability to generate mineralization. Accordingly, predominant porphyry-type mineralizations occurred during the growth rather than waning stage of a magmatic system.

     

结合遥感和气象数据的森林火险监测研究——以马来西亚半岛为例

结合遥感和气象数据,基于可燃物引燃能量的物理概念,利用火灾敏感性指数(FSI)进行森林火险监测和评估。计算FSI只需要两个参数,即可燃物的温度和湿度,两者均可以从遥感和气象数据获得。利用遥感数据进行可燃物类型制图,并根据可燃物易燃性对FSI的值进行调整计算。利用MODIS探测的火点数据对马来西亚半岛火灾前9天的FSI进行了比较分析,发现随着火灾发生日期的接近,FSI的值逐渐升高,这个趋势在火灾发生的前4天中表现的尤其明显。结果表明,FSI将遥感数据和气象数据两者紧密结合在一起,能够很好地对森林火险进行监测和预警,是一种性能优越的火险评价指数。FSI可用于计算可燃物的点燃概率以及在不同的生态系统中进行火险的比较,并且因其灵活性和可扩展性,有利于不同类型火险模型的集成和发展。     

The effects of variable speeds of a submarine block slide on near-field tsunami amplitudes

In this study, the motion of a submarine block slide, with variable velocities, and its effects on the near-field tsunami amplitudes are investigated. The numerical results show that the amplitudes generated by the slide are almost the same as those created by its average velocity when , where is average velocity of the slide and is the long period tsunami velocity in ocean of constant depth h. In contrast, the kinematic model of the slide must take into account time variations in the moving velocity, if , especially when .     

Cretaceous Environments of Afghanistan:A Synthesis Based on Selected Sections

The Cretaceous of Afghanistan is marked by great facies diversity. The evolution of Cretaceous basins is part of a complex accretionary history involving three distinct tectonic units namely the Asian (Russian) Block separated from the Indian plate by a rather well defined transcurrent fault (Chaman-Nuski). The southwestern component is representedby the Iran-Afghanistan plate. The Lower Cretaceous of the Asian Block is represented by the Red-Grit Series which isconformable to the underlying Upper Jurassic sequences. The transition is marked by evaporitic facies dominated by salt,gypsum and marl deposits. In south Afghanistan volcanic rocks occur at Farah, with the emplacement of plutonics inwest-central Afghanistan. The Upper Cretaceous of north Afghanistan is marked by richly fossiliferous, lime stone-dominated sequences. The Upper Cretaceous of southern Afghanistan is marked by strong ophiolitic magrmatism.     

Groundwater investigation in Kuala Selangor using vertical electrical sounding (VES) surveys

Integrated geoelectrical and hydrochemical surveys were used to investigate and delineate different types of groundwater in the Kuala Selangor alluvial aquifer. Previous hydrogeological borehole investigation showed that this aquifer contains several types of groundwater in relation to its salinity. The high salinity of the groundwater in some areas is believed to be due to either saltwater intrusion from the nearby sea or river infiltration during high tide season. The vertical electrical sounding (VES) method was employed to study and map the subsurface variation of resistivity in the area. For each sounding measurement, a total spread length of 300 m was obtained with a vertical depth penetration of about 60 to 75 m. Chemical analysis of the groundwater samples taken from both shallow and deep boreholes was carried out for the water quality determination. A total of 45 VES stations were succesfully established along three parallel roads with a direction almost perpendicular to the coastal line. The distance between stations varies from 1 to 2 km with a maximum length of about 60 km surveyed line. Results of the vertical electrical soundings as well as the hydrochemistry of the groundwater samples show that the soil and groundwater in the study area can be grouped into fresh and brackish water zones. The subsurface resisitivity sections derived from the VES study suggest that the area is dominated by brackish soil and groundwater zones, especially in the area towards the coast. This result appears to agree well with the groundwater pumped from boreholes scattered around in the area. Water drawn from boreholes near the coast showed higher salinity compared to the water pumped from inland boreholes. Chloride values greater than 250 mg/L are considered to represent the brackish zones whilst values less than 250 mg/L represents zones of fresh soil and groundwater.