March 17, 2017 Aigars Ievins

Renovation works on Hardombäcken drainage channel

Holistic drainage management means actions to fields, drainage and watersheds. Essential part of holistic drainage management are flow control constructions, which are wetlands, sedimentation ponds, bottom dams, regulation dams and flood plains. Ponds and flood plains can increase volume of a channel, reclaim nutrients and soil particles, decrease maintenance demand of the channel and increase biodiversity. Prior to the beginning of the channel renovation, in October 2016, two large sedimentation ponds, two bottom dams and 100 m of flood plain was constructed.

The bottom dams were built to stair shape, to ensure access of migrating fish.

The bottom dams were built to stair shape, to ensure access of migrating fish.

All to gether 400 m of flood plain was built. This increases the volume of the channel and prevents floods. This decreases out flow of nutrients and solids, and improves farming circumstances. The soil mass from the excavations is used for lifting the lowest parts of the fields. A flood plain is suitable only on territories, where the height difference between field level and ditch bottom is small.

Flood plain of the upstream section. The territory has been suffered on severe floods due to insufficient volume of the channel. Prior to approval of the construction, several discussions took place with the farmer.

Flood plain of the upstream section. The territory has been suffered on severe floods due to insufficient volume of the channel. Prior to approval of the construction, several discussions took place with the farmer.

Finally the farmer agreed, for prevention of floods and lifting the lowest field sections with excavated soils. By agreement the 300 m long flood plain could take 3 m of the cultivated field.

Finally the farmer agreed, for prevention of floods and lifting the lowest field sections with excavated soils. By agreement the 300 m long flood plain could take 3 m of the cultivated field.

Regulated dams can reserve water during dry, low flow period of summertime. This maintains water pressure on the channel, preventing erosion of the ditch slopes and excessive drying of soil. The photo of regulation dam construction, mounted to culvert of field pathway. In wintertime and during overflows the dam is open.

The bottom dam was mounted downstream from the territory suffering of ditch slope collapse.

The bottom dam was mounted downstream from the territory suffering of ditch slope collapse.

Culverts on wrong mounting level and with incorrect sizing cause floods. Clogged and damaged constructions also cause problems.

Culvert structure before and after the renovation. Photo on the right, initial situation: tree culverts of which the lowest is under water, the upper part of the middle culvert is visible and overflow culvert is totally dry.

Culvert structure before and after the renovation. Photo on the right, initial situation: tree culverts of which the lowest is under water, the upper part of the middle culvert is visible and overflow culvert is totally dry.

Cleaning of the channel dropped water levels up to 1,2 m. Renovation of the drainage network decreases floods, improves soil structure and fertility, decreases outflow of nutrients and solids. Holistic drainage management of a drainage catchment area gives benefits both to the agricultural production and to the environment.

A territory suffering of rust accumulation before and after maintenance.

A territory suffering of rust accumulation before and after maintenance.

Renovation was executed as one side excavation. The slopes were maintained untouched as much as possible.

Floods cause damages not only to soil structure and harvest, but also to roads and buildings. The culvert under road to Lapinjärvi was so clogged, that during the spring 2016 water almost got to the road. Renovation of the channel dropped water level 1,2 m. The culvert was washed and silt removed after the excavations.

Before and after the renovation.

Before and after the renovation.

Mikko Ortamala,
Drainage planner