When it rains in the desert of Patagonia: heavy rains, sediment laden flash floods and hazard management challenges.

Ephemeral streams in dry environments can produce high intensity sediment-laden flash floods. The research of these events is quite difficult due to far locations with limited accessibility, unexpected events, and rough weather conditions. Hence combined data of rainfall, flood hydrograph and sediment transport is rather scarce in the world. Recent extreme events (RI > 550 years) in arroyos (ephemeral streams) of the central Patagonia (Argentina) has called the attention of public and scientific community. The Sagmata basin (total drained area of 129 km2), located in the Lower Valley of the Chubut River (Province of Chubut, Argentina) has been equipped with 4 raingauges, a weather station, four cameras and sediment sampler in four reaches of the arroyos. Data from a two-year monitoring provides valuable insights about the hydrological response of basins in Patagonia, such as the time of response, the shape of hydrographs and its relations with the hyetographs and duration curves. The arroyos are wetted a short period of the time (8 to 21 hours a year). Single-peak, multi-peak and flat top hydrographs have been observed. The lag-time decreases with the increase of the rainfall intensity and the maximum water stage. Moreover, the bore front moves with mean speed which value is between 0.8 to 1.6 m s-1. The wash load in the arroyos depends on geological settings and vegetation cover of the basin. Mean values are between 23 – 46 gr l-1. The complex hydrograph shape produced by the basin has been linked to the rainfall features (duration, mean intensity and patchiness) and the basin physiography of the basin. Findings from the present study provide valuable information both for the comprehension of arroyos in drylands and hazard management as well.

Bedload transport measurements on the Maros river, Hungary

Sediment transport is a vital component in hydrological and fluvial geomorphological studies, however, the temporal and spatial changes in sediment fluxes, and the efficiency of bedload samplers are rarely analysed, as bedload measurements are quite difficult. The aim of the present study is to measure the bedload transport of the sand-bedded Maros River (Hungary) at low stages using the Helley-Smith bedload sampler. In order to understand the variability in the bedload transport, the water stage and discharge across the channel section were also measured. The variability of the bedload was caused by an active in-channel bar and translational sediment pulses. The created bedload transport rating curve could be applied just below 300 m3/s water discharge thus further measurements are needed to evaluate the bedload transport of higher discharges.

Assessment of an Ultrasonic Water Stage Monitoring Sensor Operating in an Urban Stream

The monitoring of the water stage in streams and rivers is essential for the sustainable management of water resources, particularly for the estimation of river discharges, the protection against floods and the design of hydraulic works. The Institute of Marine Biological Resources and Inland Waters of the Hellenic Centre for Marine Research (HCMR) has developed and operates automatic stations in rivers of Greece, which, apart from their monitoring role, offer opportunities for testing new monitoring equipment. This paper compares the performance of a new ultrasonic sensor, a non-contact water stage monitoring instrument, against a pressure transducer, both installed at the same location in an urban stream of the metropolitan area of Athens. The statistical and graph analysis of the almost one-year concurrent measurements from the two sensors revealed that stage differences never exceeded 7%, while the ultrasonic measurements were most of the time higher than the respective pressure transducer ones during the low flow conditions of the dry period and lower during the wet period of the year, when high flow events occurred. It is also remarkable that diurnal air temperature variations under stable hydrologic conditions had an impact on the measured stage from the ultrasonic sensor, which varied its stage measurements within a small but non-negligible range, while the pressure transducer did not practically fluctuate. Despite a slightly increased sensitivity of the ultrasonic sensor to meteorological conditions, the paper concludes that non-contact sensors for the monitoring of the water stage in rivers can be useful, especially where danger for possible damage of submersible instruments is increased.

Chemical and microbial evaluation of water samples obtained from itinerant water vendors in Idi – Araba, Lagos State, Nigeria

This study was carried out to investigate the potability of vendor waters mostly used by the urban dwellers in Idi-Araba, Lagos State, Nigeria. Sixteen water samples were analyzed, eleven from water vendors and four from source (Pumped Wells). One water sample from Nigerian bottling company was used as a control standard. Chemical analysis of the various water samples showed that they contained little and insignificant amount of toxic metals such as cadmium, nickel, lead and silver. Microbiological studies showed that vendor water was more contaminated than the source water and the contamination involved indicator and pathogenic organisms. All the organisms found in source water and more were found in vendor water. Susceptibility studies showed that of all the antibiotics used, the quinolones (Ofloxacin and Ciprofloxacin) and also aminoglycoside (Gentamycin) were the most effective antibiotics against the isolated microorganisms while Cloxacillin was the least active. The results of this investigation therefore suggests that the use of vendor and source waters in Idi-Araba appear unsafe for human consumption and domestic use. There is therefore the need for government and relevant authorities/organizations to provide potable water, stage awareness campaign and mass education on hygienic principles amongst the inhabitants of Surulere and the water vendors in particular.

The Use of Dam Environmental Vulnerability Index (DEVI) for Assessing Vulnerability of Bengawan Solo Watershed, Indonesia

Bengawan Solo is the longest river in Java, but current conditions show that its watershed is in a critical condition. Deforestation was very intensive in the last three decades that contributed to degradation of the watershed. Other factor contributing to the degradation is dam construction. However, our knowledge on the impact of dam construction on the environment and its vulnerability is poorly understood. Here, we assessed vulnerability of the watershed based on physical properties such as existing dams, morpho-dynamic activities, and deforested area. The study aims to identify the vulnerability of the Bengawan Solo watershed based on dam environmental vulnerability index (DEVI) approach, and to analyse the dominant variable contributing to DEVI. For calculating DEVI, several data were needed including land cover, rainfall, stream water stage, soil type, stream network, and dams. The results showed that Bengawan Solo watershed had moderate to high vulnerability (60%). Moderate level was identified for Madiun and Wonogiri sub-watershed, while high level was in Cepu and Babat sub-watershed. Our findings revealed that morpho-dynamic activities as represented by sediment rate and stream water stage had contributed to the high DEVI value as in Cepu and Babat sub-watershed. Further, influence of dams in this research was not dominant implying that any improvement to the DEVI approach remains research challenges. The improvement of the approach is expected to better identify the impact of dam construction on environment, situated in other regions than Amazon, where it was firstly developed.

Precipitation and water stage variability under rapid developments of urbanization in Taihu Basin

As one of the most developed regions in China, hydrological process of Taihu basin was influenced under rapid development of urbanization. Based on original gauge data and water stage correction data from Bureau of Hydrology, variability in precipitation and water stage was investigated by Mann–Kendall test. The results demonstrated that: (1) The highest water stage (HWS), lowest water stage (LWS), average water stage (AWS) of all months had increasing trends, especially significantly in non-flood season. The LWS also increased significantly in May, July, September, and November, while the AWS increased significantly in September and November. (2) Water diversion from Yangtze River to Taihu Basin and supplying to the downstream, had strong effects on water stage increase of Taihu Lake. Finally, recommendations based on the correlation between precipitation and water stage was proposed to protect effective utilization of water resources from the impacts of rapid urbanization.