# Planning MAR Schemes Using Physical Models: Comparison of Laboratory and Field Experiments
## 2 Materials and Methods  
### Physical Models  
The setup of the experiments was designed to allow for the comparison of flow processes during MAR under different model concepts, as described in [PERSON] et al. [27]. Three physical models of different size and dimensionality were constructed for this study, as follows: A 1D-column in the laboratory (H = 1 m, diameter = 0.15 m), a rectangular-shaped 3D-infiltration tank in the laboratory (L = 1.5 m, W = 1 m, H = 1 m), and a rectangular-shaped 3D-infiltration unit in the field (FIU) without confinement (L = 4.5 m, W = 3 m, H = 1 m) (Figure 1). The FIU is situated in Pirna, Germany. The laboratory scale units were placed inside of a climate-controlled glasshouse, whereas the FIU was influenced by the local temperature, humidity, and solar radiation (temperate continental climate, Table 1). A transparent roof prevented the influence of precipitation at the FIU in all scenarios, except scenario 1. The experiments in the laboratory scale units took place at a constant air temperature (17 \({}^{\circ}\)C) and humidity (70%), similar to the daily averages of the mild climate of the FIU. The laboratory models were packed with a fine sand for the first set of experiments (Soil 1: hydraulic conductivity \(K_{f}\): \(1.7\times 10^{-4}\) m/s; 94.5% sand, 4.5% silt, 1% clay) and a slightly siltier fine sand for the second set of experiments (Soil 2: \(K_{f}\): \(4.8\times 10^{-5}\) m/s; 92.3% sand, 7% silt, 0.7% clay), with a filling height of 0.85 m. In the FIU, the same soils were placed directly in an excavated basin within the local soil material, which consists of anthropogenic fillings and fine alluvial sands resulting from flood events of the Elbe river [28]. Soils were compacted manually in the laboratory and with the help of a vibrating plate in the FIU. To control stratification, soils were built in with defined interval heights (10 cm in the laboratory units, 30 cm in the field). For each height, the soil was raked at the top after compaction and before filling in new soil material in order to avoid sharp interfaces. The bulk density was determined for each interval height. Values were very similar over the depth of the profile, as follows: From 1.56-1.61 g/cm\({}^{3}\) in the tank and 1.62-1.67 g/cm\({}^{3}\) in the field (for soil 2). All units were operated with the same set of varying infiltration scenarios. River water (dissolved organic carbon \(\approx\) 5 mg/L, total suspended solids \(\approx\) 20 mg/L) was infiltrated at a hydraulic loading rate (HLR) of 300 m/a. The hydraulic loading cycles (HLC) defining wet-dry ratios and the duration of infiltration phases were varied between the infiltration scenarios (Table 1). The infiltration of water was regulated through infiltration basins installed in the center of the units (size of basin in tank: W = 0.3 m, L = 0.45 m, H = 0.06 m, in FIU: W = 0.9 m, L = 1.35 m, H = 0.06 m, in column: complete soil surface). Infiltration into the systems was conducted by flooding the entire soil surface from a small pipe above the center of the surface. Infiltration rates, based on HLR, HLC, and the infiltration area, were 2.7 L/min (scenario 1-3) and 0.9 L/min (scenario 4) for the FIU, 0.3 L/min (scenario 1-3) and 0.1 L/min (scenario 4) for the tank, and 0.04 L/min (scenario 1-3) and 0.013 L/min (scenario 4) for the column. In the FIU, the lower boundary was directly connected with the vadose zone, ensuring free drainage. The lower boundary in the laboratory consisted of a filter disc (column) and grating with gravel filter (tank) connected with a free drainage outlet. The spatial and temporal distribution of soil moisture for every setup was measured by a tensiometer (tensio160, UGT GmbH) and a water content probe (UMP-1, UGT GmbH) each in 0.3 m (upper layer--UL) and in 0.7 m depth (lower layer--LL) below the center of the infiltration basin. The water content probes have a measurement volume of 1 L and probes were not installed in the column.