Long-term control of the effectiveness of the surface sealing system on the sarbor sediment disposal site Hamburg-Francop
Type:
Presented during:
WODCON XVII: "Dredging in a Sensitive Environment" - 2004, Hamburg, Germany
Authors:
A. Gröngröft, K. Tresselt, K. Berger, C. Harms&B. Maass
Abstract: Sediment dredged from the port of Hamburg is treated and stored upland in a storage facility. The site is covered by a system of topsoil above a sand drainage layer and a barrier layer made of processed harbor sludge in order to minimize the input of water. For the long-term monitoring of the water balance of the cover system two test fields of 500 m2 each have been constructed. The layer structure of these fields permits a) to quantify the water balance of the surface cover system being realized on the Francop site as a standard and b) to investigate the meaning of a considerably smaller root area on feared desiccation of the barrier layer. Both fields are equipped with an automatic measurement data recording device for the determination of the discharges as well as of selected meteorological and soil-hydrologic parameters. On the basis of measured data of the first 8 years the test field with the standard layer design showed only small annual discharges through the barrier (mean 17 mm/a). Therefore the function of the cover system is continuously fulfilled. Substantial meaning comes thereby in particular to the material properties of the drainage layer and the harbor sludge barrier. In contrast, the test field which was constructed to force the desiccation behavior, showed effects of desiccation after the 4th summer. The development of an aggregate structure led to a failure of the barrier after the 5th summer. A visual control of the soil profile and accompanying laboratory tests indicated, that the change was caused by intruding roots into the barrier layer.
Keywords: upland sediment disposal, surface sealing, barrier performance