NECs monitoring at le Sorelle B pilot site

NECs monitoring

to Journal

Vital Team
on 10.03.22

The resilience of salt marshes in the Venice Lagoon with respect to the rise in mean sea level depends considerably on sedimentation dynamics (both organic and inorganic), erosion and compaction.

We speak of autocompaction when the compaction of recently deposited, soft sediments occurs. Claudia Zoccarato - an environmental engineer at the University of Padua and part of the Vital team - has recently shown that to compensate for the rise in sea level expected over the next hundred years, sedimentation will need to occur at twice the current rate. This shows us how important it is to monitor sedimentation dynamics in natural environments. For the same reason, it is important to study these processes in controlled environments such as reconstructed salt marshes. Vital has recently installed one Nourishment Elevation Change (NEC) monitoring system on an artificial salt marsh in the Lagoon.

View from the pilot site Sorelle B. Foto Claudia Zoccarato.

'Sorelle B' is the pilot site of the artificial salt marsh project conducted by Vital.

Ten NEC stations have been installed at the end of September 2021 to measure both the autocompaction of sediments and the subsidence of the underlying layers. The elevation of each NEC station is monitored to millimeter accuracy with a topographic intersection technique using a total station, with two stable benchmarks positioned in a nearby artificial salt marsh used as reference. The change over time of the NEC elevation allows to measure subsidence of underlying strata. Topographic intersection surveys have been conducted every fortnight since restoration began in October 2021. During the first month of new sediment input, a maximum subsidence of approximately 7 cm was detected from the NEC station closest to the input pipe. Moreover, the NECs are monitored using aerial drone photogrammetry to quantify autocompaction of the newly deposited sediments. The NEC monitoring system looks promising and will provide quantitative data on the elevation dynamics of the newly created artificial marshes.