River or lake bed sediment clogging strongly affects the proportion and volume of bank filtrate. It occurs due to the entrapment of the pore space through biological, chemical, mechanical and physical processes. Physical clogging is especially important in warm climates such as in tropical areas due to the considerable weathering, which causes decomposition of rocks and the enrichment of water bodies with fine particles. Field experiments in the Peri Lake (Brazil), using seepage meters showed a mean infiltration rate of 1.4E-6 m s-1 in the lake shore, and no significant difference was observed between vegetable (V) and nonvegetable (NV) zones. Using the same measuring method, the Lake Tegel presented infiltration rates of around 1.2E-6 m s-1 in winter and summer in NV areas. In V areas slightly lower infiltration rates were measured in winter (9.2E-7 m s-1) than in summer (1.7E-6 m s-1). Both Peri and Lake Tegel have a low potential of physical sediment clogging. Groundwater flow modeling of the potential BF site at Peri Lake showed that high abstraction rates deteriorate infiltration distribution, and cause a strong decrease in groundwater levels and higher drawdown in the production wells. Column experiments to study the effect of the grain form, showed that at an infiltration rate of 2.0E-5 m s-1fine sand presented 0.2 logs more reduction in K-values than fine glass beads. Coarse sand presented a K-value reduction 6.6 times higher than coarse glass beads at similar infiltration rates. Using channel experiments with kaolinite as suspended sediment and fine sand in the columns of the channel, a K-value reduction of 1.6 logs was observed at high and low flow condition in the channel. Turbidity values of 300 NTU and a mean infiltration rate of 2.1E-4 m s-1 were applied in the columns. Similar results were observed by using 900 NTU of turbidity. By using coarse sand a reduction of 0.8 and 1.4 orders of magnitude of K-values was observed, under the same hydraulic conditions cited above and suspended sediment concentration of 300 and 900 NTU, respectively. By using well graded sediment in the channel experiments, K-values of the upper 10 cm of sediment were reduced by almost 2 orders of magnitude within 24 hours. In a long term low flow condition simulation of the Elbe River associated with high infiltration rates K-values dropped by more than 2 orders of magnitude within 84 days. An external clogging of 4 cm depth was observed with 65.5 % of the grains being smaller than 60 µm, and an increase of total organic matter (TOC) to 45,940 mg kg-1. A channel experiment under transient conditions at the Ping River in Thailand demonstrated a K-value reduction of one order of magnitude in 48 hours for the upper 3 cm of sediment. Sediment clogging was related to high turbidity values as well as high infiltration rates applied in the system. The well design and abstraction rates have to be adapted to the periods of low flow condition of the river in order to avoid strong sediment clogging. A maximum infiltration rate of 0.32 m3 m-2 d-1 should avoid sediment clogging caused by infiltration force actions and might be taken as maximum reference for rivers with high turbidity values.
|Advisor:||Gunkel, GünterGrischek, Thomas|
|School:||Technische Universitaet Berlin (Germany)|
|Source:||DAI-C 81/1(E), Dissertation Abstracts International|
|Subjects:||Geological engineering, Environmental engineering, Environmental Geology|
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