Sediment formation, transport and sedimentation, including sediment-water interactions
H. Boernick (TUD), B. Steiniger (TUD), M. R. Bilich (UnB), H. L. Roig (UnB), P. Junker (UnB), C. Lorz (TUD), F. Makeschin (TUD), T. P. Trindade (Caesb), G. Abbt-Braun (KIT), E. Worch (TUD), N. M. de Souza (UnB) [from left to right]
Silting of reservoirs is a major problem for reservoir management and might be a threat for water supply in Brasilia DF, because (i) sediments reduce volumes of reservoirs and (ii) sediments might be sources for nutrients and pollutants (remobilization).
Sediments have two principal sources (fig. 1), first slope systems and second alluvial flood plains. Slope systems (soil-regolith-relief) react mainly to climatic conditions (intensity and duration of rainfall) and land use. While sheet and rill erosion (laminar erosion) are mainly induced by farming activities, gully erosion is mostly a product of ill maintained infrastructures (road drainage, sewers etc.). In alluvial plains remobilization of sediments might occur, that is mainly driven by lateral erosion during storm events. Peaks of sediment transport are reached before hydrological peaks. Reservoirs are final sinks for sediments. Within reservoirs only sedimentation rates and sediment properties are of interest.
Figure 1: Sediment cascade
Our research within working group 4 aims firstly at sediment budgets and sediment management. Sediment budgets will identify major sources and sinks in the slope and alluvial plain system. From these facts measures to minimize sediment generation and transport into reservoirs should be obtained.
Another main task consists of the comprehensive characterization of the sediments, in particular in view of heavy metals, organic micropollutants, nutrients, and carbon content.
Based on the results of the chemical analyses a first risk assessment about the remobilization potentials will be done. In a second step, defined leaching procedures will be used to simulate changing environmental conditions and predictions will be made based on different future scenarios provided by working group 1 (climate) and 2 (land consumption and land use).
- Information of generation, transport and deposition of sediments
- Characterization of sediments regarding organic contaminants, nutrients and heavy metals
- Studying the role of internal nutrient loadings as a contribution for eutrophication processes in Lake Descorberto and Lake Paranoá
- Assessment of sediment potential to transport/mobilize pollutants (organics, heavy metals) via complex formation/sorption and release
- Sediment budget and management
Material and Methods
In the R. Torto river network we sampled sediments from alluvial floodplain soils (fig. 2), to develop an idea on sediment rates and ages of sediments.
Figure 2: Alluvial floodplain soil near R. Torto, north of Brasília
We are currently developing a planning support tool - Letsmap do Brasil – for minimizing sediment input into surface waters. The tool will be used to support stakeholders in participating at decision processes. Letsmap do Brasil is an integrative approach considering other important landscape functions.
Figure 3. Test simulation with letsmap do Brasil for a catchment with (a) scenario arable land (real land use), (b) scenario fruit plantation, (c) scenario afforestation, (d) scenario Cerrado
Figure 4: Map of the sampling points for sediments in the Lake Paranoá
In the first sampling campaign a sediment core (2.80 m) was taken in the part of Lake Paranoá with the highest anthropogenic impact. Selected slices were analyzed for TOC/TIC, heavy metals and selected organic micropollutants.
Figure 5: Picture of the sliced-open sediment core
In a further sampling campaign surface sediment samples of Lake Paranoá were taken at selected places in branches of the lake and close to the inflow of the tributaries. Based on the results of the first sampling campaign the samples will be screened for selected heavy metals and organic micropollutants.
In the next step, first predictions about the remobilization potential will be made. Furthermore, it is planned to implement defined leaching procedures which allow the simulation of changing environmental conditions (e.g. climate change).
- F. Bakker, Companhia de Saneamento Ambiental do Distrito Federal – Brasília (CAESB)
- Prof. F. Makeschin, PD. Dr. C. Lorz, Technische Universität Dresden (TUD), Department of Forest Science, Institute of Soil Science and Site Ecology
- Prof. E. Worch, Dr. Hilmar Börnick, Björn Steiniger, Technische Universität Dresden (TUD), Department of Hydrosciences, Institute of Water Chemistry
- Dr. G. Abbt-Braun, Karlsruher Institut für Technologie (KIT), Institute of Water Chemistry
- Prof. H. Roig, Universidade de Brasília (UnB), Department of Geosciences
- Prof. De Souza, Universidade de Brasília (UnB), Department of Environmental Engineering
PD Dr. Carsten Lorz | Prof. Dr. Franz Makeschin
Institute of Soil Science and Site Ecology
Dresden University of Technology
Pienner Str. 19
Phone: +49 (0) 35203 38 31 816