Figure 1: The proposed multi-module smart drainage management approach.

In the first module, the forecasted hydro-climatological data of the study area are collected and characterized in detail. The 1-10 day forecasted rainfall and temperature data, provided by regional authorities and meteorological institutes, are used as initial input. The forecasted temperature is applied to estimate the daily reference evapotranspiration (ET₀). The crop evapotranspiration (ETc) will be calculated based on the ET₀ and crop coefficient (Kc) in the different growth stages.

Using ETc, current soil water holding, and forecasted rainfall, the daily soil moisture will be estimated for the next 10 days using the Water Balance Simulation (WBS) in the hydrological simulation module. The results of the WBS will propose tentative irrigation or drainage demand values to farmers (or system operators). This provides the basis to implement optimal irrigation or drainage management.

In the first step of the implementation module, the water level in the crop field will be optimized by using the automatic drainage control system. For instance, if currently (e.g., today) the field has enough water, but no (or deficit) rainfall is forecasted within the next 10 days, the drainage valve will automatically be closed (or partially closed) to keep soil moisture near the root zone. Conversely, if an extreme rainfall event is forecasted, a drainage valve will automatically be fully opened to facilitate drainage and avoid waterlogging. WBS simulation takes advantage of the ICT sensors by considering soil hydraulic properties (e.g. soil water retention curve) to regulate the drainage outflow.

In the final part of the implementation module, the excess drained water from heavy rainfall events can be stored in a buffer pond or portable storage tank (Fig. 1). Some parts of the drainage ditch, beside the field, can be used as a buffer pond by applying a water level controller. During a summer drought, the stored water can be used for fertigation. Care needs to be taken in assessing the water quality of the stored water, thus avoiding excess fertilization and degradation of soils (i.e. through heavy metals, salinization, etc.). The assessed irrigation water can be fed back through the existing drainage system using these as underground irrigation pipes, thus avoiding additional irrigation infrastructure and using emission-free systems (e.g. solar pumps). An elevated storage tank can also help overcome the possible uncertainty in the weather predictions. A solar pump will be applied to store drained water into a portable storage tankwhich can then be used for fertigation by gravity flow. Given the climatic conditions of the Nordic region, the tank can be filled with melted water from snow before the cropping season. Additionally, the drainage water recycling reduces nutrient loading to surface water from agriculture.