A largely reactive approach to flood situations has worked well under the circumstances but the current flood management system is vulnerable and may collapse dramatically under extreme conditions, according to a report from a Dutch risk reduction team, which has urged a more proactive approach.
“Considering the economic situation of Guyana and the relatively mild character of the flooding events under normal conditions, it is not recommended to consider new large scale, expensive infrastructure. Instead, it is advised to take a large number of small steps over a period of several years that will increase the knowledge and the collective ownership of the drainage infrastructure among local experts, Guyanese governments, and the people of Guyana,” the report says.
The Dutch Risk Reduction Team had visited Guyana last year at the request of government. The Ministry of Public Infrastructure had asked the team to advise on the drainage situation, both for Georgetown and the low-lying agricultural coastlands. The report was submitted in January and among other things, identified short, medium and long term measures that can be taken to better operate and manage the drainage system of Georgetown and the low-lying coastal areas.
According to the report, the key issue overarching all topics is that the present approach in Guyana is largely reactive. “Action is generally only taken once a problem has occurred and plans are made basically on a project-by-project scale and crises-driven. This seems to have worked rather well under the given circumstances,” the report said. It cited as an example, the placement of extra mobile pumps after the discharge capacity under gravity turned out to be insufficient. It also highlighted the recent removal of solid waste, the excavation of drainage tunnels, and different agencies helping each other in case of shortage of equipment.
The report said that a proactive approach has advantages as it generally lowers flood risks and can avoid dangerous situations, which in the future may be less manageable. It said this will be the case under less favourable conditions, such as combined high precipitation and high tides.
“Due to a lack of data or statistical analysis, it is yet not possible to determine the probability of occurrence of such extreme combined events, but it is clear to the team that the current flood management system is vulnerable and may collapse dramatically under such unprecedented conditions,” the report said. It made several recommendations for ongoing support aimed at making the Guyana approach towards water management more proactive. The report pointed out that much needs to be done but also acknowledged budget constraints, and, as a result, the recommendations were made with this in mind.
The report urged that government upgrade modelling capability even as it noted that the current practice of maintaining and improving the drainage system is largely projects-based. It recommended that the authorities make a long-term project plan to gradually develop the hydraulic drainage model for Georgetown. It also urged the setting up of a simple spreadsheet type of network model for the entire drainage system of Georgetown and use it to better understand the flow of water. “Use this understanding to support project proposals (for example increasing the pumping capacity of the most northern outfall sluice along the Demerara River),” the report said. It also urged the government to start selecting two or three engineers with a passion for computers and modelling and train them on the subject of hydraulic modelling.
“A computer (hydraulic) model could be such a tool, so that project proposals can focus on those measures that have maximum contribution to the functioning of the whole drainage system. Costs for setting up and running a computer model are always significantly lower than the benefits that come with better predictions and better design of critical infrastructure. Modelling saves money and will result in considerable improvement of the current drainage,” the report said.
‘Living with water’
Another recommendation was to improve flood resiliency of people. The report urged government to develop a communication plan with the aim to increase the understanding of the people about what it means to live with water – in terms of potentials and challenges – and execute this plan. “It has to be clear that the flood risk will never be reduced to zero,” the report said.
It urged that a flood hazard map of Georgetown be made and used to explain to the people why it is important to build their properties flood-proof. The report also recommended the preparation of a simple explanation, for example a YouTube video, on how the drainage system works, why water needs space, and why it is important to keep the drainage system free from constructions and solid waste.
“Most people will be aware of flood threats when it happens and forget about it soon after. This loss of awareness influences their behaviour regarding the existing water management infrastructure such as neglecting its function,” the report observed.
Further, the report recommended that small-scale floating dredging capabilities be upgraded. It said that a good way to maintain the city’s drainage channel at locations where excavation from the landside is not possible, would be by floating mini dredgers, such as cutter suction dredgers. In the Netherlands as well as in many other countries, these mini dredgers are often used to dredge channels in highly urbanised areas or in situations where nearly fluid mud needs to be removed.
The report said that the requirements for small scale floating dredgers for Georgetown could be specified and the investment justified based on a cost/benefit calculation. Either a public or a private entity could run the “City Dredging Operations,” and after the purchase of equipment and the start of operations, the performance could be evaluated on a regular basis.
Further, the report recommended the development and application of a rational risk approach. “Improving and maintaining the drainage system is a rational and in fact ‘smart’ investment if the associated costs are lower than the reduction in flood risks. Since available budgets are always limited, it is important to select those (improvement or maintenance) measures that lower the flood risk most. Today’s practice in Guyana in proposing improvement measures seems to be primarily projects-based, without an assessment of the whole drainage system. This implies that the chosen measures may in the end not have the largest reduction of the flood risks,” the report observed.
It recommended the preparation of a first set of flood hazard maps and the setting up of the framework for analysis for the sea defence risk assessment using the Rational Risk Approach. The Rational Risk Approach is a consistent (probabilistic) method that analyses all elements of the flood defence system, it computes failure probabilities of each element under a wide variety of extreme conditions (each with their own probability of occurrence), it computes the (monetary and nonmonetary) consequences of any such failure, and it multiplies the probability of floods with all potential consequences. By doing so, valuable information is gained on the weakest parts of the defence system.
It also recommended the setting up of a ‘Living with Water’ pilot project in which all elements of an integrated long-term and holistic “Drainage System Management” are specified and made applicable to Guyanese situations. “The most logical pilot would be a new development that aims to create enough space for water from the beginning and to design attractive recreational spaces around drainage canals,” the report said.
Data management
The report also recommended the development and application of a life cycle approach for drainage assets. “Looking at the drainage system from an asset management perspective, it becomes evident that managing the drainage system is a continuous process that requires ongoing attention in order to keep it functioning (operations, maintenance), to improve it to acceptable levels (Risk Approach based), and to make it future proof (climate change, economic development),” the report said.
It also urged improved data management. The report said that data are collected by different Departments and Agencies and coordination on data collection and management – where to store it and how to use it in decision-making processes – seems to be not effective enough. It urged that all available data on the drainage system – Georgetown and elsewhere – be collected, digitised, and gap analysis applied to see what is missing. It also urged the collection of other data such as all relevant hydro-meteorological data that is required for a risk assessment of the drainage system as well as the sea defence system and use a pre-set format for such data collection and store it in a national central data base.
It said the data can be analysed in a consistent manner in order to contribute to better understanding of the flood risks. Further, Lidar data in combination with land use data can be used to prepare flood hazard maps while long-term rainfall data can be used to determine the frequency of occurrences of extreme rainfall events, which serves as input for the risk assessment.
The report also recommended technical short-term improvements, such as upgrade of sluices and the increasing of the hydraulic efficiency of the tertiary and secondary drainage system.
“The lack of a knowledge infrastructure and institutional memory may well be the largest barrier for improvement of the Guyanese water systems. A lot of knowledge is available in the heads of the people involved but it is not combined, it is not accessible to others and there are no foundations laid for further knowledge development. Maps and graphs with monitoring data, numerical models assessing the potential impact of climate change, digital databases and evaluation reports are needed,” the report said.
It said that improvements of the operation and management of the drainage system is possible and necessary. “Frequent inundation is a threat to the economic development as well as to public health. The frequency of today’s flood events in Georgetown is rightfully no longer accepted by the authorities. This implies that the drainage system needs to be upgraded and adequately managed,” the report said.
It noted that probably the most obvious running initiative to consider co-funding is the Budget Support programme from the European Union even though this focusses on the sea defence. It said that preliminary discussions on this subject with the EU representative in the preparation of the mission indicated that this could indeed be an option.