Spatio-Temporal Monitoring Of Floodplain Environments Using Electromagnetic Methods: A Scaled Approach To Understanding Surface Water- Groundwater Interactions On The Chowilla Floodplain, South Australia
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Geophysical methods are used in Australia to provide detailed spatial information to help predict the impact of current and future irrigation developments, the design of salt interception schemes and protection of floodplain values. RESOLVE frequency domain helicopter electromagnetic data were acquired over the Chowilla Floodplains, in the Lower Murray region of southern Australia, to provide detailed baseline data on the spatial distribution of near-surface salt stores and materials in the floodplain and their relationship with in-river salinity. Degradation across the floodplain and wetlands has resulted primarily from a significant reduction in flood events, and overgrazing. Restoration of the floodplain will involve the reduction of salinity flow from groundwater into the river and increasing H87environmental flows across the floodplain. Conductivity models predicted from HEM data help identify local recharge and discharge areas,<br>and links with river salinity. The baseline data provided by the airborne data are used with high resolution ground EM surveys including EM31 and time-domain EM, over targeted areas. Ground methods can be repeated, to monitor affects of artificial flooding designed to restore vegetation health. Similarly the combination of airborne and ground data, allows piezometers to be effectively targeted with the resulting information interpreted within the context of the baseline conductivity structure defined form airborne data.The 100-year floodplain is the traditional indicator of flood risk and the area in which specific flood mitigation requirements are required to occur in the United States. However, recent studies have indicated that there is a growing disconnect between the 100-year floodplain and the location of actual losses. As a result, there is a strong need to understand what is undermining the efficacy of the 100-year floodplain and to generate a more accurate depiction of flood risk. However, there have been few studies that examine the characteristics of insured flood claims occurring outside the 100-year floodplain and how more advanced hydrologic models may improve flood risk delineation. This study addresses this issue by cross-validating a fairly new distributed hydrologic flood inundation model and the Federal Emergency Management Association's 100-year floodplain with historical, parcel-level insured flood losses in two subbasins near Houston, Texas. Results illustrate that spatially distributed hydrologic models greatly improve floodplain delineation, provide important insights on the drivers of flood damage outside of the floodplain, and offer alternative ways to more effectively communicate flood risk.
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Numerous restoration campaigns focused on re-establishing species-rich floodplain meadows of Central Europe, whose species composition is essentially controlled by regular flooding. Climate change predictions expect strong alterations on the discharge regime of Europe's large rivers with little-known consequences on floodplain meadow plants. In this study, we aim to determine the effects of flooding on seedlings of different ages of four typical flood meadow species. To this end, we flooded seedlings of two familial pairs of flood meadow species of wetter and dryer microhabitats for 2 weeks each, starting 2, 4, 6, and 8 weeks after seedling germination, respectively. We show that a 2-week-flooding treatment had a negative effect on performance of seedlings younger than 6 weeks. Summer floods with high floodwater temperatures may have especially detrimental effects on seedlings, which is corroborated by previous findings. As expected, the plants from wet floodplain meadow microhabitats coped better with the flooding treatment than those from dryer microhabitats. In conclusion, our results suggest that restoration measures may perform more successfully if seedlings of restored species are older than the critical age of about 6 weeks before a spring flooding begins. Seasonal flow patterns may influence vegetation dynamics of floodplain meadows and should, therefore, be taken into account when timing future restoration campaigns.
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Abstract. This paper looks into flood events of the past 500 years in the SW Netherlands, addressing the issue of what kind of flooding events have occurred and which ones have mainly natural causes and which ones are predominantly human induced. The flood events are classified into two major categories: (a) flood events that were caused during storm surges and (b) flood events which happened during warfare. From both categories a selection of flood events has been made. Each flood event is discussed in terms of time, location, extent of the flooded area and specific conditions. Among these conditions, specific weather circumstances and how long they lasted, the highest water levels reached and dike maintenance are discussed as far as flood events caused during storm surges are concerned. Flood events during warfare as both offensive and defensive strategies are relevant; the paper demonstrates that although the strategic flood events obviously were man-made, the natural feature, being the use of fresh water or sea water, of these events also played a major role. Flood events caused during storm surge may have an obvious natural cause, but the extent of the flooding and damage it caused was largely determined by man.
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