Drainage of an ice-dammed lake through a supraglacial stream: hydraulics and thermodynamics

The glacier-dammed Lac des Faverges, located on Glacier de la Plaine Morte (Swiss Alps), has drained annually as a glacier lake outburst flood since 2011. In 2018, the lake volume reached more than 2 × 106 m3, and the resulting flood caused damage to the infrastructure downstream. In 2019, a supraglacial channel was dug to artificially initiate a surface lake drainage, thus limiting the lake water volume and the corresponding hazard. The peak in lake discharge was successfully reduced by over 90 % compared to 2018. We conducted extensive field measurements of the lake-channel system during the 48 d drainage event of 2019 to characterize its hydraulics and thermodynamics. The derived Darcy–Weisbach friction factor, which characterizes the water flow resistance in the channel, ranges from 0.17 to 0.48. This broad range emphasizes the factor's variability and questions the choice of a constant friction factor in glacio-hydrological models. For the Nusselt number, which relates the channel-wall melt to the water temperature, we show that the classic, empirical Dittus–Boelter equation with the standard coefficients does not adequately represent our measurements, and we propose a suitable pair of coefficients to fit our observations. This hints at the need to continue research into how heat transfer at the ice–water interface is described in the context of glacial hydraulics.

Drainage of an ice-dammed lake through a supraglacial stream: hydraulics and thermodynamics

The glacier-dammed Lac des Faverges, located on Glacier de la Plaine Morte (Swiss Alps), drained annually as a glacier lake outburst flood since 2011. In 2018, the lake volume reached more than 2 × 106 m3 and the resulting flood caused damages to the infrastructure downstream. In 2019, a supraglacial channel was dug to artificially initiate a surface lake drainage, thus limiting the lake water volume and the corresponding hazard. The peak in lake discharge was successfully reduced by over 90 % compared to 2018. We conducted extensive field measurements of the lake-channel system during the 48-days drainage event of 2019 to characterize its hydraulics and thermodynamics. The derived Darcy-Weisbach friction factor, which characterizes the water flow resistance in the channel, ranges from 0.17 to 0.48. This broad range emphasizes the factor’s variability, and questions the choice of a constant friction factor in glacio-hydrological models. For the Nusselt number, which relates the channel-wall melt to the water temperature, we show that the classic, empirical Dittus-Boelter equation with the standard coefficients is not adequately representing our measurements, and we propose a suitable pair of coefficients to fit our observations. This hints at the need to continue the research into how heat transfer at the ice/water interface is described in the context of glacial hydraulics.

Approaches for assessing riverine scour

Calculating scour potential in a stream or river is as much a geomorphological art as it is an exact science. The complexity of stream hydraulics and heterogeneity of river-bed materials makes scour predictions in natural channels uncertain. Uncertain scour depths near high-hazard flood-risk zones and flood-risk management structures lead to over-designed projects and difficult flood-risk management decisions. This Regional Sediment Management technical report presents an approach for estimating scour by providing a decision framework that future practitioners can use to compute scour potential within a riverine environment. This methodology was developed through a partnership with the US Army Engineer Research and Development Center, Hydrologic Engineering Center, and St. Paul District in support of the Lower American River Contract 3 project in Sacramento, CA.

Purifikasi Alami Sungai Bedadung Hilir Menggunakan Pemodelan Streeter-Phelps

Latar Belakang: Sungai Bedadung hilir berada di Kabupaten Jember dan merupakan bagian sungai utama di DAS Bedadung. Sungai ini berperan penting bagi kehidupan masyarakat Jember. Kegiatan pengunaan lahan mengubah fungsi sungai menjadi saluran pembuang limbah. Limbah organik masuk ke badan air Sungai Bedadung dan menurunkan oksigen terlarut di perairan.Metode: Penelitian ini merupakan penelitian deskriptif. Data primer diperoleh dengan melakukan pengukuran debit dan kualitas air (Temperatur, DO dan BOD) sungai di lima titik pantau. Data tersebut kemudian diolah dan digunakan sebagai input variabel persamaan Streeter-Phelps.Hasil: Berdasarkan penelitian yang dilakukan laju deoksigenasi dan reoksigenasi Sungai Bedadung hilir tertinggi berada pada BDG02 masing-masing 7.997 mg/L.hari dan 19.168 mg/L/hari. Purifikasi alami yang dimodelkan dengan persamaan Streeter-Phelps, pada BDG02 tidak menunjukkan tren penurunan oksigen terlarut, sedangkan empat titik yang lain cenderung turun, mencapai kondisi kritis dan saturai di waktu yang berbeda. Hasil pembuktian model menunjukkan terjadi perbedaan nilai DO model terhadap kondisi lapangan (DO aktual).Simpulan: Aplikasi pemodelan Streeter-Phelps untuk menganalisis purifikasi alami Sungai Bedadung tidak dapat menunjukkan kesesuaian dengan kondisi lapang, karena proses deoksigenasi dan reoksigenasi di sepanjang sungai selalu berbeda dengan model bergantung pada tambahan pencemar dan hidraulik sungai. ABSTRACTTitle :Background: Bedadung Downstream, at Jember Region, is the primary river of Bedadung basin. The river has its meaningful advantages to public activities. Change of land uses the stream functions to a big drainage channel. Organic pollutants entrance to the water body and decrease the concentration of dissolved oxygen.Methods: This research was descriptive. The primary data was obtained by measuring stream flows and water quality (Temperature, DO, and BOD) at five observed stations. The data were processed and used as variable inputs to the Streeter-Phelps equation.Results: Based on the research conducted, BDG02 had the highest values of deoxygenation and reoxygenation rates, which were 7.997 mg/L.day and 19.168 mg/L.day respectively. DOmod at BDG02 tends to line up, whereas DOmod at four stations had a tendency to declined to critical conditions and rise to the saturation condition at different times. DO sag model was different from actual DO, which measured directly in the water body.Conclusions: The use of the Streeter-Phelps equation to analyze the self-purification of Bedadung downstream wasn’t appropriate with the field conditions. Deoxygenation and reoxygenation process in the river body was typically difference with the model applied, which were affected by organic pollutants and stream hydraulics.