How can negative effects on water quality be mitigated?

The measures in the “Management and maintenance” cluster – intended to manage and maintain the water system – pertain to, e.g., mowing, dredging, and weed control.

• Dredging watercourses: regular removal of the layer of mud from the bottom of ditches, canals, and lakes, in order to, inter alia, create more room for water;
• Keeping birds away and/or enforcing a feeding ban;
• Environmentally friendly weed control;
• Removal of waste near trash racks, culverts or weirs;
• Leaves removal at river banks;
• Clearing away blue-green algae;
• Flushing the water after sewer overflows;
• Duckweed removal from the water;
• Intensive water plant management;
• Leaves removal from the water.

The measures in the “Water chain” cluster address the actual water chain and involve, e.g., adjustments to the sewer system of changes in flushing regimes.

• Creating a bioswale or soil passage to disconnect paved surfaces from the sewer system. Bioswales are primarily intended to slowly drain water into the soil, whereas soil passages are mainly intended to filter the water;
• Installing a storage settling basin or filters at sewer overflows, to keep dirt from ending up in surface water;
• Detecting faulty sewer connections.

The measures in the “Hydrological functioning” cluster improve water behaviour and characteristics, for example, by allowing free flow or enabling the intake of clean water.

• Modifying intake regimes: adapting the frequency or rate of water intake from another watercourse;
• Taking in water from another source;
• Dephosphating inlet water: removing phosphates from the water;
• Relocating inlet to a freshwater location;
• Expanding a culvert to optimise the connection between two watercourses;
• Raising or lowering a culvert to optimise the connection between two watercourses;
• Connecting bodies of water, for example, by constructing a culvert;
• Restoring seepage effect (fresh water): restoring freshwater seepage from the soil.

The measures in the “Structure” cluster adapt the water system profile. For example, a water system can be rendered deeper or shallower. Another example is interconnecting multiple bodies of water.

• Cancelling dog walking locations;
• Creating a buffer zone between a road and a watercourse;
• Providing collection points for emptying underwater toilets;
• Making water deeper;
• Making water shallower;
• Planting hedges on river banks;
• Planting trees on river banks;
• Fostering water circulation;
• Granting or revoking permits for cold water discharge and/or warm water collection;
• Installing a fountain or bubble screen to aerate the water, in order to boost oxygen content.

Issues resulting from a deteriorating water quality cannot always be prevented. In such cases, clear communication with water consumers is helpful. Another measure could be accepting that a particular use will not always be possible.

• Communication on hygiene regulations;
• Communication on health risks of swimming and other water leisure activities;
• Acceptance of issues such as stench or fish mortality;
• Acceptance of changing ecological quality.

The water quality may have deteriorated to such an extent as to preclude certain functions. In such cases, measures could be considered to switch to alternative functions.

• Harvesting duckweed: a new method of producing protein;
• Farmers in salinised areas may switch to saline crops, which are irrigated with saline water in addition to fresh water.

The measures in the table are categorised in three types: prevention, adaptation and acceptance. These categories are explained below.

1. Prevention: measures that prevent further deterioration of the water quality. For example, filtering water containing micro pollutants before run-off; disconnecting downspouts to prevent sewer overflows; or constructing a buffer system in areas dependent on river water.
2. Adaptation: measures that mitigate any negative effects of climate change. For example, more frequent flushing of deteriorating surface water; or providing shade around surface water.
3. Acceptance: measures to accept a change in or deterioration of the water quality. For example, by capitalising on opportunities opened up by such changes, such as switching to saline crops. Or by raising awareness of risks to encourage changes in human behaviour, such as communicating on blue-green algae at non-official swimming locations, to prevent people from going for a swim there.

Below the indicators, the table distinguishes between effect-oriented and source-oriented measures:

• The effect-oriented measures are intended to mitigate the effects of climate change. Such effects affect an indicator as a whole.
• The source-oriented measures are intended to remove the source of negative effects. These measures affect specific control variables.

For example, “Clearing away blue-green algae” targets the effect of directly improving the indicator of nutriment content and does not address any of the sources of excessive blue-green algae growth. “Leaves removal from riverbanks”, on the other hand, addresses a source of excessively high nutriment content in surface water. That is why the box indicating the Leaf Fall control variable in the table is coloured green and marked with an A, as the measure will reduce leaf fall.