# Reconstruction of Ancient Lake after Peat Excavation--A Case Study about Water Quality
## 2 Materials and Methods
### Shaping of the Post-Peat Reservoir  
The construction of the studied reservoir (III) was carried out in several stages and was preceded by the construction of two smaller post-peat reservoirs I and II (Figure 2). After peat exploitation in the northeastern part, both parts of the reservoir were separated by a causeway and part A was flooded with water. The remaining part (B) was then drained by pumping out water in order to exploit the dry peat. After the extraction of the peat deposit, the reclamation work began, including the appropriate shaping of the surrounding area and bottom, levelling the banks and softening the slopes of the planned water reservoir and then, filling it with water. The reservoir is filling out a depression formerly occupied by lake and its banks are not reinforced in any part. Since the excavated deposit was formed as a result of the eutrophication of the former glacial lake, the construction of the water reservoir in this place was in a sense the reconstruction of an old, natural reservoir of glacial origin and contributed to the regulation of water conditions in this area.  
Prior to the peat deposit exploitation, the groundwater level was regulated by a system of drainage ditches, and the outflow of water went in the northwestern direction, through a 30 cm diameter pipeline with a culvert at the northern boundary of the area. Additionally, the watercourse Slomowo was periodically (during months with relatively high precipitation) supplying the reservoir with water, as shown in Figure 2. Precipitation in 2015 (446 mm) was lower than average (523 mm during the period 1981-2010).  
The slopes of the reservoir were made of moraine clay and create an impermeable basin, limiting the water penetration into the surrounding land. The water level in the reservoir corresponds to the natural hydrological conditions, determined by the land char  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Peat Characteristics** & **Unit** & **Minimum** & **Maximum** & **Average** & **Standard Dev.** \\ \hline \hline Spoil thickness & (m) & 0.1 & 0.2 & 0.18 & 0.04 \\ Deposit thickness & (m) & 0.4 & 3.4 & 2.0 & 0.7 \\ Degree of decomposition & (\%) & 43 & 79 & 59.1 & 8.7 \\ Ash content & (\%) & 11 & 39 & 24.2 & 7.9 \\ \hline pH reaction & (-) & 6.1 & 7.4 & 7.0 * & 0.4 \\ \hline \hline \end{tabular}  
* Median.  
\end{table}
Table 1: Parameters of the peat deposit in Nienawiszcz.  
acteristics. The available resources of the reservoir are positively influenced by numerous natural springs occurring around the lake.  
As a result of the undertaken works, a unique water reservoir with natural lake slopes and a very extensive and picturesque coastline was formed. The post-mining land was naturally filled with water from local springs, through the existing system of drainage ditches and precipitation. There was no need for damming up the water in this case, as there is a constant inflow of groundwater in this area, supplemented by periodical surface inflow.  
After the peat deposit was excavated, a post-mining water reservoir was created (Figure 3). The average depth of post-peat lake was equal to 1.64 m and the maximum depth was 3.99 m. The length of the coastline was equal to 2425 m. The volume of reservoir was about 175,322 m\({}^{3}\) and the area equal to 11 ha (including island) (Table 2). The total area of the water surface was equal to 10.71 ha. The maximum water level was determined by the lowest edge of the culvert positioned at 87.09 m above sea level. The reservoir has a diversified shoreline, covered with forests, meadows, and arable lands; it also has an island, days of different depths and four peninsulas covered with grass.