Natural disasters such as floods, drought, hurricanes, winter storms, and earthquakes can disrupt access to clean drinking water. These events can result in any number of types of water service disruptions including pipe breaks and leaks; power outages; infrastructure failure; reduced water quality; loss of access to facilities and supplies; as well as financial, social, environmental and health consequences.
Being able to quickly respond and reduce loss of service is an important characteristic of a community’s resiliency and the goal of water utilities across the country. To improve their resilience, communities, and the utilities that provide drinking water to these communities, are building their capacity to recover and return to service as quickly as possible, planning for and understanding any potential vulnerabilities in their system, and practicing response to adverse events in real-time as they happen.
To help communities and their drinking water utilities, researchers from EPA and the Sandia National Laboratories developed the Water Network Tool for Resilience (WNTR), a comprehensive scientific software package to help assess a drinking water systems’ resilience to natural disasters. The software improves upon already available capabilities by fully integrating hydraulic and water quality simulation, damage estimates and response actions, and resilience metrics into a single platform. The software is available as an open source software package and can be applied to a wide range of disruptive incidents and repair strategies.
“The WNTR software package can help drinking water utilities estimate potential damages from a disaster, understand how the damage to infrastructure might occur over time, evaluate preparedness strategies, prioritize response actions, and identify worse case scenarios and efficient repair strategies,” explains EPA researcher, Terra Haxton. “WNTR includes a variety of models, it has flexible controls, hydraulic simulations, and resilience metrics and it is compatible with EPANET, EPA’s software application that is used worldwide to understand the movement and fate of drinking water within a distribution system.”
WNTR can simulate scenarios when the treatment plant is disconnected from the system. One drinking water utility working with the research team wanted to investigate how long their system could continue to supply water to their customers if they were unable to pull and treat water from the river due to water quality issues. These issues included salt water intrusion from drought conditions, chemical spill from tanker accidents, or freezing of the intake itself. WNTR was able to help the utility understand which customers would be affected first and what steps could be taken to reduce any downtime for customers.
Drinking water utilities often want to identify which pipes are most critical to their system operations by identifying vulnerabilities throughout the system. WNTR can assist with this analysis because it includes a feature that simulates the movement of water under low pressure conditions as it travels from the utility to businesses and residences throughout the system. This analysis highlights which specific pipe breaks would cause problematic low pressure, thereby reducing the amount of water delivered to the customer. This feature also helps to discover which areas of the system might have low pressure during a firefighting incident. This information helps utilities determine which pipes are most critical to maintain, rehabilitate or repair to be better prepared for disasters.
The impact of a power outage on a drinking water system is important to drinking water utilities. WNTR can help determine the effects of a power outage by simulating the removal of pumps and tanks from the system operations and can simulate the impact to customers, and help identify where to invest in back up power.
The primary modeling components of WNTR include:
- Disaster models, for example, attenuation models that predict ground movement after an earthquake
- Fragility curves used to assign the probability of damage to network components
- Flexible controls to change the status and operation of network components
- Models to estimate leaks in the system
- Pressure Dependent Demands (PDD) hydraulic simulation to model a network during low pressure conditions
- Resilience metrics to evaluate the effect of disruption and repair strategies
- The ability to perform Monte Carlo simulations, to understand the impact of risk and uncertainty of the simulation parameters
WNTR can also assist utilities with requirements of the America’s Water Infrastructure Act of 2018 (AWIA). AWIA requires community (drinking) water systems serving more than 3,300 people to develop or update risk assessments and emergency response plans (ERPs). The law specifies the components that the risk assessments and ERPs must address and establishes deadlines by which water systems must certify to EPA completion of the risk assessment and ERP.
For more information about WNTR, please visit: https://github.com/USEPA/WNTR
Klise, K.A., Bynum, M., Moriarty, D., Murray, R. (2017). A software framework for assessing the resilience of drinking water systems to disasters with an example earthquake case study, Environmental Modelling and Software, 95, 420-431, doi: 10.1016/j.envsoft.2017.06.022