11Riverbank filtration schemes form a significant component of public water treatment processes on a 12 global level. Understanding the resilience and water quality recovery of these systems following 13 severe flooding is critical for effective water resources management under potential future climate 14 change. This paper assesses the impact of floodplain inundation on the water quality of a shallow 15 aquifer riverbank filtration system and how water quality recovers following an extreme (1 in 17 16 year, duration > 70 days, 7 day inundation) flood event. During the inundation event, riverbank 17 filtrate water quality is dominated by rapid direct recharge and floodwater infiltration (high fraction 18 of surface water, dissolved organic carbon (DOC) > 140% baseline values, > 1 log increase in micro-19 organic contaminants, microbial detects and turbidity, low specific electrical conductivity (SEC) < 20 90% baseline, high dissolved oxygen (DO) > 400% baseline). A rapid recovery is observed in water 21 quality with most floodwater impacts only observed for 2 -3 weeks after the flooding event and a 22 *Revised manuscript with no changes marked Click here to view linked References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 return to normal groundwater conditions within 6 weeks (lower fraction of surface water, higher 23 SEC, lower DOC, organic and microbial detects, DO). Recovery rates are constrained by the 24 hydrogeological site setting, the abstraction regime and the water quality trends at site boundary 25 conditions. In this case, increased abstraction rates and a high transmissivity aquifer facilitate rapid 26 water quality recoveries, with longer term trends controlled by background river and groundwater 27 qualities. Temporary reductions in abstraction rates appear to slow water quality recoveries. 28Flexible operating regimes such as the one implemented at this study site are likely to be required if 29 shallow aquifer riverbank filtration systems are to be resilient to future inundation events. 30Development of a conceptual understanding of hydrochemical boundaries and site hydrogeology 31 through monitoring is required to assess the suitability of a prospective riverbank filtration site.

We assessed the utility of online fluorescence spectroscopy for the real-time evaluation of the microbial quality of untreated drinking water. Online fluorimeters were installed on the raw water intake at four groundwater-derived UK public water supplies alongside existing turbidity sensors that are used to forewarn of the presence of microbial contamination in the water industry. The fluorimeters targeted fluorescent dissolved organic matter (DOM) peaks at excitation/emission wavelengths of 280/365 nm (tryptophan-like fluorescence, TLF) and 280/450 nm (humic-like fluorescence, HLF). Discrete samples were collected for Escherichia coli, total bacterial cell counts by flow cytometry, and laboratory-based fluorescence and absorbance. Both TLF and HLF were strongly correlated with E. coli (ρ = 0.71-0.77) and total bacterial cell concentrations (ρ = 0.73-0.76), whereas the correlations between turbidity and E. coli (ρ = 0.48) and total bacterial cell counts (ρ = 0.40) were much weaker. No clear TLF peak was observed at the sites and all apparent TLF was considered to be optical bleed-through from the neighbouring HLF peak. Therefore, a HLF fluorimeter alone would be sufficient to evaluate the microbial water quality at these sources. Fluorescent DOM was also influenced by site operations such as pump start-up and the precipitation of cations on the sensor windows. Online fluorescent DOM sensors are a better indicator of the microbial quality of untreated drinking water than turbidity and they have wide-ranging potential applications within the water industry.

Effective management of groundwater resources during drought is essential. How is groundwater currently managed during droughts, and in the face of environmental change, what should be the future priorities? Four themes are explored, from the perspective of groundwater management in England (UK): (1) integration of drought definitions; (2) enhanced fundamental monitoring; (3) integrated modelling of groundwater in the water cycle; and (4) better information sharing. Whilst these themes are considered in the context of England, globally, they are relevant wherever groundwater is affected by drought.

The Chalk aquifer is often considered as a single, homogeneous, isotropic groundwater system in regional groundwater management studies, even though it has been subdivided into several different lithostratigraphic units. Low-permeability layers, including marl bands and hardgrounds, extend on a regional scale and define different layers within the Chalk. Four case studies in different locations of the Chalk aquifer of SE England are presented: (1) a multi-level observation borehole in the Upper Colne catchment in Hertfordshire; (2) different water levels in shallow and deep boreholes in the River Ver catchment; (3) artesian conditions and rises in the groundwater level during drilling in the Chiltern Hills; and (4) groundwater level separation in a public water supply borehole in Kent. The evidence clearly shows a layered system in the Chalk and vertical hydraulic discontinuity within the studied sequences. The current conceptual model of the Chalk aquifer should be enhanced to include this new understanding and to update the existing numerical groundwater models. This will, in turn, increase confidence in the current decision support tools for environmental sustainability and the management of water resources in the Chalk aquifer.

&lt;p&gt;The Chalk is considered an important aquifer in the Southeast of the UK as it supports flows in ecologically sensitive Chalk streams, as well as significant groundwater abstractions for public water supply purposes. Based on the Water Framework Directive (EU directive) objectives, all rivers need to be in good ecological status or support good ecological potential by 2027. The environmental regulatory body (Environment Agency) have designated the area located Northwest of London as over-licensed and over-abstracted in terms of groundwater availability from the Chalk aquifer. As a result of this, a long-term management strategy has been proposed, allowing for significant groundwater abstraction reductions for implementation between now and 2050.&lt;/p&gt; &lt;p&gt;Whilst under a range of river flow conditions, the proposed abstraction reductions are expected to allow greater baseflow to enter the rivers, it is possible that under higher flow conditions there will be an elevated risk of flooding, especially in downstream locations. An alternative approach is presented in this case study near London, aiming to utilise the well-established river-aquifer interactions during a range of hydrological conditions to balance the effects of winter floods and low flows during droughts.&lt;/p&gt; &lt;p&gt;The proposal for this case study is in an unconfined Chalk aquifer setting, supporting a number of groundwater abstractions, as well as providing baseflow to a river which is also supported by an effluent discharge. A nearby surface water reservoir located on top of clay deposits, is also available but currently unused for public water supply. Groundwater abstractions in the area are known to be supported by river flows during drought conditions, via a leaky river bed. Based on river bed leakage assessments undertaken under different hydrological conditions, it was found that a certain proportion of the total river flow can recharge the unconfined chalk aquifer via the leaky river bed in a 2-3 km stretch of river.&lt;/p&gt; &lt;p&gt;Therefore, the idea of capturing high river flows above a certain trigger at a downstream location through the urban areas where the river is in a concrete channel and refilling the currently disused reservoir storage, has been explored. Instead of then having to treat this water as surface water before using it for public water supply, by releasing this water back into the river at the head of the catchment during times of low flows it could support both river flows and also the output of the groundwater sources via artificial leakage. This unconventional type of Managed Aquifer Recharge has been tested under various hydrological conditions and could also prove a cost-effective scheme due to the lack of additional treatment needed for the surface-derived water.&lt;/p&gt; &lt;p&gt;This study demonstrates that enhanced understanding of the natural processes in a river catchment can provide alternative ways of managing the effects arising from both flood and drought events, whilst creating a resilient water supply in a changing climate.&lt;/p&gt;