Quantifying intra- and inter-annual dynamics of river-floodplain
connectivity and wetland inundation with remote sensing and wavelet
analysis.
Abstract
We used imagery from remote sensing (FORCE Time Series Analysis
submodule (combining Landsat and Sentinel-2 imagery)) to derive
spatially distributed times series (8 years) of NDWI data to infer
patterns of floodplain inundation and river-floodplain connectivity in
two contrasting polders in the Lower Oder Valley National Park. The
upstream Polder A (14.4 km 2) was extensively flooded
for prolonged periods most winters. Wavelet analysis showed that this
strong seasonality was primarily driven by winter water levels in the
river Oder that could enter and leave the polder through two opened
flood gates. Subsequent drainage was slow and aided by a pumping
station. Inundation of the downstream Polder 10 (17.7km
2) was lower and had less marked seasonality. This
reflected the impact of flood attenuation by storage in Polder A
upstream, but also the greater connectivity (via 10 flood gates) to the
Oder and a functional network of channels which facilitated rapid
drainage after flood peaks. In Polder A, secondary periods of transient
inundation could also occur in response to local intense summer
rainfall. Wavelet analysis also showed that groundwater recharge in and
around Polder A is primarily induced by floodwater, whilst Polder 10
also reflects the influence of local rainfall-driven recharge. The flood
regimes of the two polders showed marked inter-annual variation, largely
dependent on flows from the upper Oder catchment. Understanding these
patterns and processes of inundation is important for both managing
flows and sustaining valuable wetland habitats within the National Park.
Given projected climate change in eastern Europe and possible management
alterations to the flow regime of the Oder, the potential implications
for these habitats needs urgent attention.