Calculation of suspended sediment deposition intensity in grass-covered floodplains

Abstract

 bstract Flooded river valley meadows are ve^ important for river ecology, as they entrap sediments and ŝ ediment-bound nitrogen or heavy metals. Nevertheless, the grass-covered fioodplains, particularly in river j deltas, are often separated from the rivers by dykes. Wtien such systems are designed, it is necessary to model sediment deposition in these separated areas. However, the existing calculation methods and models are g adapted for flow over the sandy bottom. In the meadow flows there are other boundary conditions more > favourable for sediment deposition. £The focus of our studies was the processes of suspended sediment deposition in the flooded delta ot the fP River Nemunas. Calibration results of the mathematical model with common sediment deposition formulae for r iverbed flows did not correspond to the data of measurements. The differences were obvious. Consequently, it S was necessary to study the peculiarities of How and sediment motion under these conditions, as well as to work *« out formulae suitable for calculations.

Mathematical Modeling of the Suspended Sediment Dynamics in the Riverbeds and Valleys of Lithuanian Rivers and Their Deltas

“…Thus, the volume of sediments deposited in the floodplain is quite large. Such amounts of sediments per unit floodplain area have been found in our field investigations (Rimkus & Vaikasas, 2010;Rimkus et al, 2007;Lamsodis & Vaikasas, 2005;Vaikasas & Rimkus, 2003). In periodically flooded meadows, the grasses actually entrap the sediments and favour self-cleaning of the rivers.…”

“…Sediment deposition in the Nemunas valley was calculated applying our own hydraulicmathematical model "DELTA" created for the study of the Nemunas delta ( Fig. 2) (Rimkus et al, 2004(Rimkus et al, , 2007. The known mathematical models (MIKE 21 1995) were not applicable for our purpose because they are not adapted for sediment deposition calculations in the flooded meadows, for which the special formulae are to be applied.…”

“…However the sedimentation process in grassed food plains was yet not investigated properly. Method for calculation of sediment deposition in the grass-covered floodplain, proposed by Rimkus, was created with estimation of grass ability to entrap the sediments (Rimkus et al, 2007). Because of the low flow velocity between the grasses, the sediment deposition in them becomes similar to the deposition in still water.…”

“…For fine clay sediments, it is received F=1. This sediment deposition calculation method is described in detail in the published articles (Rimkus et al, 2007;Rimkus & Vaikasas, 1999). Sediment deposition calculations were performed according these formulae.…”

Possible ways to improve sediment deposition in the Nemunas delta

“…Sediment deposition in the Nemunas valley was calculated by applying our own hydraulic mathematical model DELTA, created for the study of the Nemunas delta (Rimkus et al 2004(Rimkus et al , 2007. The model was supplemented for these investigations to enable better estimation of any peculiarities of the variants under study.…”