Increase and preserve freshwater reserves

Water management always has been an expertise of the Dutch. Even their King has a master title in water management… Yet, their focus is partly shifting from keeping the seawater out and staying safe, to increasing and preserving freshwater levels.

The higher likelihood of severe droughts with (possible) bans on irrigation and salination in especially coastal areas, have led to various research projects and solutions to preserve freshwater in periods of abundance to increase the availability in periods of shortage.

Actively controlled drainage

Deltares, a Dutch research institute has trailed three different concepts in the past years in the Southwestern Delta of the Netherlands to increase the availability of freshwater and to drain brackish and salt water. Two of these involves actively controlled drainage. Actively controlled drainage is constructed in different ways:

Drain pipes no longer drain superfluous precipitation to ditches or creeks, but via vertical water collector pipes with a float to keep the level of groundwater higher, or
Drain pipes no longer drain superfluous precipitation to ditches or creeks, but to vertical water collector tanks with pumps that infiltrate the water deeper in the soil, or
The water level in ditches or creeks in which the drains drain superfluous precipitation, is controlled with a weir (stuw) to keep the level of groundwater higher

_{The video below gives an impression of how actively controlled drainage works}

3 concepts

The concepts Deltares researched in the GO-FRESH project in the Southwestern Delta of the Netherlands are: the Freshmaker concept, creek ridge Infiltration (infiltration via drainage) and Drains2Buffer (actively controlled drainage). Creek ridges are ancient or historic sandy waterways able to contain and store freshwater. Interesting is that they also calculated the cost of each of the concepts:

Freshmaker: € 4,500 to € 9,000 per hectare equalling € 815 to € 1,225 per hectare per year. This makes it only viable for high value crops such as vegetables
Creek ridge Infiltration: € 3,200 to € 4,750 per hectare equalling € 510 to € 790 per hectare per year. Per cubic metre / 1,000 litres, the cost are € 0.16 to € 0.18 which makes it viable for arable crops like potatoes and onions
Drains2Buffer: € 1,950 to € 2,900 per hectare equalling € 260 to € 380 per hectare per year which makes it viable for many arable crops

Installation of an actively controlled drainage system in the province of Limburg, the Netherlands. - Photo: Bert Jansen
The Freshmaker (left) infiltrates freshwater into creek ridges via the upper drainage pipes while the lower pipes drain brackish/saline groundwater. With creek ridge infiltration, groundwater levels are raised and controlled via actively controlled drainage. Every 10 cm of extra groundwater captured during the winter, increases the freshwater level by 10 cm. Drains2Buffer is especially suited for lower regions and uses also actively controlled drainage via deeper drainage pipes resulting in an increased fresh water volume and drainage of brackish/saline water. - Source: Go-Fresh
Directional drilling for the installation of horizontal wells/filters of the Freshmaker concept. Two filters of 70 m each were installed. - Photo: Go-Fresh
Drainage pipes being installed for the creek ridge infiltration system. - Photo: Go-Fresh
The vertical water collection pipe of the creek ridge infiltration system is the part of the actively controlled drainage system in which a float controls the water level. This indirectly also controls the water level in the drainage pipes. - Photo: Go-Fresh
A view down the vertical water collection pipe with the supply pipe from the drainage system also visible. - Photo: Go-Fresh
In another type of creek ridge infiltration system, these collector tanks are installed to collect the water from the drainage pipes. - Photo: Anton Dingemanse
Drainage specialists install a (blue, vertical) infiltration pipe via a 22 m deep and 50 cm wide hole. Only the lower 4 m of each pipe is porous for the infiltration of fresh water into sandy creek ridges. This way, a freshwater storage is built up during winter for irrigation during dry summer periods. - Photo: Anton Dingemanse
With a temporary weir installed, farmers maintain higher water levels by containing the wintery precipitation which normally results in 70 - 100 cm water levels in this particular ditch. - Photo: Peter Roek
Inflatable balloons are used to temporary block waterways to prevent the water from draining and to keep ditch water levels higher. Even skippy balls are used to do this but those cannot be deflated if the water needs to drain again. - Photo: Peter Roek