Surface water connectivity dynamics of a large scale extreme flood

Abstract

During flood inundation, river water passes from the main channel into the floodplain through floodplain channels and diffusive overbank flow. This flood water is then distributed within the floodplain depending upon internal connections, barriers and storage, and finally returns back to the river through drainage connections. This surface water connectivity can be complex and is important to many aspects of floodplain functioning, including ecology, sediment movement and flood risk. However, there is currently no accepted way of quantifying this connectivity objectively. We quantify surface water connectivity geostatistically as an objectively measurable characteristic of an observed flood event using a time series of MODIS (Moderate Resolution Imaging Spectroradiometer) surface water product for an extreme large scale flood event (11,000 km 2 flooded area and 6 month duration) during 2011 in Bangkok, Thailand. We develop and apply a new gap filling method that better preserves the dynamic information of the event than simple aggregation methods. Comparison of MODIS results with the higher resolution Earth Observer 1 shows fundamental differences in the resolved connectivity with scale despite similar flooded area. The effect of the passage of the flood wave is directly observable in the river reach, as out-of-bank flooding progresses and increases connectivity along the river during rising water. Around peak flow, there is an increase in connectivity of the floodplain adjacent to the river as low lying areas fill. A step increase in connectivity is correlated with a major levee breach. During recession there is a rapid reduction in along river connectivity in the first week after the peak. This rapid reduction contrasted with a slow decrease in the floodplain connectivity as flooded depressions gradually drained reducing depth, while flood extent remained static for long periods. The connectivity analysis of the threshold in floodplain draining indicates that although spatial flood extent changes are small at this time, there is a reorganisation of the internal surface water connectivity within the flooded area. Thus through this measure of connectivity, we can see a clear structure to the event progression with new insights into flood dynamics that were not anticipated a priori.

The effects of topographic depressions on multiscale overland flow connectivity: A high‐resolution spatiotemporal pattern analysis approach based on connectivity statistics

“…We examined the flow snapshots for this period and found that overland flow is gradually drained out of the topography, but the maximum lag distance of the connected flow pathways remains at approximately half of the maximum lag distance of the watershed, that is, connected flow can still extend across half of the watershed scale (regardless of flows in stream channel or floodplain). This finding is consistent with other studies that have described how, during recession limbs, flow slowly spills out of low laying areas (depressions) but remains connected within the scale of these areas (e.g., Trigg, Michaelides, Neal, & Bates, 2013) 3.3 | Role of depressions on overland flow connectivity changes across spatial scales-direction…”

Hyporheic flow and transport processes: Mechanisms, models, and biogeochemical implications

“…There has been a recent tendency toward merging the concept of hyporheic flow, which occurs at all times [ Buffington and Tonina , ], with classical concepts of bank storage [ Pinder and Sauer , ; Sophocleous , ] and overbank flow [ Mertes , ; Tockner et al ., ; Trigg et al ., ] that are caused by fluctuating water levels during spates and floods. The effect that river flooding has on hyporheic flow through bar and riffle features has been widely investigated [ Gariglio et al ., ; Nowinski et al ., ; Shope et al ., ; Francis et al ., ; Käser et al ., ; Wondzell and Swanson , ; Harvey et al ., ].…”

Impact of climate change on floodplain inundation and hydrological connectivity between wetlands and rivers in a tropical river catchment

“…Remote sensing methods have the ability to acquire information on inundation and surface water connectivity over large areas relatively cheaply (Bates, 2004;Chen et al, 2013;Trigg et al, 2013;Dzubakova et al, 2015). However, affordable remotely sensed products have limited application for evaluating wetland connectivity.…”