Water management manual – a guide to managing a water damming facility

In the face of natural disasters such as flooding or drought, water retention facilities focus our attention. We expect their effective use in minimizing the negative effects of these phenomena. Water management instructions provide a scenario for dealing with various hydrological circumstances, including extreme ones.

Water damming facilities

Water damming facilities that require water management instructions may include those listed and briefly described below:

• Storage reservoirs are tanks that permanently store water for flood control, energy, supply or environmental purposes.
• Artificial water reservoirs are all reservoirs used to store water, such as for industrial, energy, irrigation or recreational purposes.
• Dry flood reservoirs are hydraulic structures that are usually empty and their main function is to retain excess water during flood periods to reduce the risk of flooding in downstream areas, once the flood wave recedes the reservoir gradually empties.
• Polders are low-lying areas surrounded by dikes that can be inundated in a controlled manner to reduce the flood tide on a river, and the water is gradually discharged once the danger has passed.
• Weirs are hydraulic structures that are used to dam up water in rivers or other watercourses, especially in the context of flow regulation and flood protection.
• Water stages are complexes of facilities consisting of a weir and one or more navigation locks. These facilities are used to provide transit depths on navigable rivers and enable watercraft to overcome the difference in the upper and lower water tables.
• Other flood control facilities – other hydraulic structures that are relevant to flood risk management, such as flood gates, embankment locks, etc.

Water management manual – scope

Any facility damming water, including, most notably, a flood control reservoir (wet or dry), polder, water stage or weir, must have a water management instruction (IGW). The scope and content of the instruction is defined in detail in the Regulation of the Minister of Maritime Affairs and Inland Navigation dated August 21, 2019. on the scope of water management instructions ( OJ. 2019 pos. 1725 ).

A reservoir water management manual is a document that defines the rules for managing water resources at a hydroelectric facility. Its purpose is to optimize water management in a way that ensures both flood protection and the fulfillment of other tasks, such as water supply, energy production, environmental protection, water transportation or recreation. In the case of a cascade of reservoirs or water stages, there is a single, common instruction that covers all damming facilities and those of relevance to a particular section of the river.

Main elements of the manual:

• Rules for filling and emptying the facility – determine the optimal water levels in the reservoir depending on the season, hydrological situation and weather forecasts.
• Emergency management – includes procedures in case of flood, drought or other extraordinary circumstances, with the aim of minimizing the risk of danger to life and damage to property and the environment.
• Water flow management – specifies how to regulate the flow of water in the river downstream of the reservoir to maintain adequate water levels both during periods of heavy rainfall and in times of drought.

When it applies:

• Under normal hydrological conditions – to ensure optimal management of water resources at the site, adapted to its function (e.g., retention, power generation, water supply);
• In extreme situations – such as floods or droughts, the instruction provides for measures to minimize losses and protect infrastructure and residents.

The regulation very precisely defines the terminology and all the required data and information that should be included in the descriptive part, graphic part or annexes. It is worth emphasizing that these are not only technical data, such as the volumes of discharges at specific states (including for warning and alarm states), but also precise information about those responsible for specific tasks, interacting entities and communication assumptions.

The manual is a kind of guide to what can be developed/changed under what conditions and on what basis within the framework of facility management. There is no arbitrariness or discretion in decision-making here. In the case of emergency events, the key is the forecasts of water inflow to the facility, on the basis of which all decisions are made. The more accurate and reliable the forecasts, the better.

In the case of large damming facilities, information about the safety of the structure is also important and can influence the course of action. Awareness of the consequences of decisions and the impact on the area below or the facility itself (e.g., environmental considerations) is also important. These variables are indeed many. However, this is not surprising, since in most cases we are talking about their importance for human safety, whether it is flooding or securing drinking water needs.

Significantly, the water management instruction shall be approved in the water permit for water use and served on all affected plants and the water owner.

Water management instructions – deviations

Under standard conditions, water management at the facility is carried out on the basis of and in accordance with the water management manual, which specifies the rules for maintaining the water level, the amount of discharge, damming, as well as specifying the procedures for action in emergency situations. However, it happens that:

• extraordinary weather or hydrological conditions (e.g., unusually heavy rainfall, rapidly melting snow, drought) may require actions that are not provided for in the standard instructions;
• water management instructions do not take into account the latest meteorological or hydrological forecasts, which may lead to decisions to discharge additional water earlier to avoid overflowing the reservoir.

The decision to discharge ahead of time, contrary to the water management manual, is made in emergency situations when:

• Meteorological forecasts point to an impending flood wave, the scale of which may exceed the reservoir’s retention capacity;
• there is a risk that standard reservoir management procedures will not be sufficient to protect areas below the reservoir from flooding;
• response time is limited, and water management authorities choose to empty the reservoir earlier to increase its retention capacity.

These decisions are made by the facility administrator. However, each time, due to their extraordinary nature, they are analyzed in detail by the control authorities. It is verified whether the decision taken is correct, especially if it will negatively affect downstream areas. In the event that actions are taken that are not in accordance with the instructions, they must be reckoned with after the threat to which they relate has disappeared.

Water management instructions – essential elements

The manual is a key tool in the management of hydrotechnical facilities and is used by reservoir administrators, primarily Wody Polskie, but also by other entities responsible for water management at damming facilities (e.g., power companies, water and sewage companies or cities). It is worth highlighting several important conditions that can affect the quality of facility management.

Timeliness of instructions

The timeliness of the instructions and the reference to the most current state of a given damming facility are of utmost importance. Implemented upgrades or condition assessments may require changes to the instructions. Changing hydro-meteo conditions and activities being implemented in the country (e.g., in the upper section of a watercourse, which will affect the flow of water at a given facility) should also be subject to regular review and update if necessary. Unfortunately, the procedure for updating instructions is so lengthy that it often discourages efforts in this direction. Perhaps here is room for a change in approach and simplification.

Forecast

Data on water inflow forecasts for most large hydrotechnical facilities are provided by IMGW-PIB. This is key information on the basis of which – in a flood emergency – certain decisions are made and action scenarios are selected. Unfortunately, not all facilities have a chance for a good or any forecast due to the lack of measurement data at the entrance to the facility (especially on smaller watercourses).

Monitoring and measurement

An element of the manual is a list of measuring devices and a description of the measurement and observation network. It is very important to have up-to-date information about the technical condition of the facility, which can be provided by monitoring, but also by the metering of its interior, allowing to accurately track, for example, the stability of the facility. Not all facilities, due to their age and period of construction, have such information. The technologies used and available now were not used several decades ago, and aging infrastructure is a problem not only for Poland, but for the whole of Europe.

Maps and scenarios

What is not written directly into the instruction regulation, but appears in many, are maps showing the extent of the facility’s impact for various scenarios, primarily flood scenarios. Not all instructions include maps of emergency risks. In 2022. PGW WP has prepared and published flood risk mapping extents for 26 damming structures – the studies were only for “wet” reservoirs. It may be worthwhile to direct attention also to dry reservoirs and polders, which can cause catastrophic consequences in case of failure.

Summary

The facility’s water management manual is created at the time of commissioning and serves as a guide for the administrator on how to proceed in order to maintain optimal conditions for the facility itself and the surrounding ecosystem. However, there are situations that are certainly not easy and that require emergency action and decision-making against the rules of the manual.