Quantifying the Impact of Flooding on Faecal Indicator Organisms in the Betna river basin of Southwest Bangladesh

Due to climate change, Bangladesh has been experiencing more frequent and intense flooding. Flooding cause epidemics of diarrheal diseases: every year more than one hundred thousand children die due to diarrhoea related diseases. Outbreaks of diarrhoea are related to the concentration of waterborne pathogens in surface waters. Sanitation and sewage treatment facilities are insufficient in Bangladesh. After heavy rainfall sewage and manure enter surface waters directly. In Bangladesh, increased concentrations of faecal indicators have been observed after flooding events. Qualitative relationships between flooding and water pathogens are established. Pathogen concentrations in surface waters can increase due to increased flooding. Increased flooding also dilutes pollutants and pathogens, and increased temperatures could inactivate pathogens. However, the relative contribution of climate variables (temperature and precipitations) to changes in pathogen concentrations remains unclear. To better understand the role of climate, the relative contribution of major climatic variables must be studied quantitatively. Such studies have not been performed yet.

Therefore, we aim to quantify the impact of flooding on waterborne pathogens. As an indicator, faecal enterococci and E. coli concentration will be measured in several locations of Betna river of Bangladesh in flooding and non-flooding periods. A coupled hydrodynamic-microbial model (e.g. MIKE 21 FM) will be applied to project microbial concentrations in these surface waters. The latest IPCC and SSP scenarios will provide climate change projections. The outcomes of this study can provide valuable information and understanding of spatial and temporal concentrations of faecal indicators and the subsequent waterborne disease risks.

Research objectives

The objective of this study is to quantify the impact of flooding on faecal indicators (enterococci and E. coli) in the Betna river basin of southwest Bangladesh. The specific objectives are:

• To measure the concentrations of faecal indicators in surface water in flooding and non-flooding periods.
• To model the current and future concentrations of faecal indicators in surface water by using a coupled hydrodynamic-microbial model (e.g. MIKE 21 FM).
• To develop a comprehensive future scenarios including for instance possible increased future flood risk, human and animal population growth, change in agriculture and aquaculture pattern.
• To assess the future impact of increased flooding due to climate change on faecal indicators by scenario analysis.

Research questions

The objectives will be achieved by answering the following questions:

1. What are the concentration levels, sources and pathways of enterococci and E. coli in the surface water of Betna river of Bangladesh in flooding and non-flooding periods?
2. How do modelled and observed current concentrations of enterococci in the surface water of the river compare?
3. What are the future projected faecal indicator concentrations in the river’s surface water with more flooding events, as expected in the context of climate change?

Methods

The study will be carried out in three steps to answer the above mentioned research questions:

Step 1. Sources and concentrations of surface water microbial contamination

To answer the first question, as a first step we will collect water sample from different locations of Betna river at different season and then perform analysis to measure enterococci and E. coli concentration. Water samples will be collected from five locations of Betna river. The locations are selected on the basis of point and non-point sources of sewage and manure discharge into the river. Surface water samples will be collected on daily basis during flooding times and once in a month during non-flooding periods. We will measure two consecutive years February 2014 to January 2016.

The water samples will be analysed at the laboratory of Khulna University. We will use membrane filtration method for determination of enterococci and E. coli concentrations from water samples.

Step 2. Model the concentrations of faecal indicators (enterococci and E. coli) in the surface water of the selected river basin

We will use a coupled hydrodynamic-microbial model (e.g. MIKE 21 FM) to forecast microbial concentrations in river water. The MIKE 21 is a two dimensional hydrodynamic model which includes a water quality module (ECO Lab) is very effective tool to project concentrations of faecal indicators in the surface water and to analyse the scenarios for future impact of flood. The model will be validated using the observational data from step 1. These data will be compared to the model output data. If the model output does not correspond with the measured data, we will go back to improve the model setup. A sensitivity analysis will be done to identify the most responsive parameters. The analysis will be done in changing some model inputs like amount of river bed roughness, wind speed, direct stream deposition from livestock, bacteria die-off rate etc.

Step 3. Scenario analysis

To understand how the microbial water quality may change in the future when flooding is expected to occur more often, a scenario analysis will be done. For this, first of all we need to develop scenarios, run the model with changed input variables and analyse the differences between the current and future concentrations of faecal indicators. We will use a similar approach with the latest IPCC and SSP scenarios to develop comprehensive storylines comprising all input variables for our model. After scenario development, the model applied in step 2 will be run with the newly developed scenarios for scenario analysis. We will try to answer the research question, what will be the impact on concentrations of faecal indicators if flooding events will occur more often and intense in the future.

The results will help to understand the current and future impacts of flooding on microbial water pollution. The result will contribute to the government initiative in developing flood risk management strategies.