borehole
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Place of groundwater extraction
The groundwater is extracted by means of a deep well at the following location:
District: Witzenhausen
Land parcel: 12
Land parcel: 20/5
borehole:
easting value: 09° 51‘ 47.93“
northing value: 51° 20‘ 48.80“
above sea level: 134,4m
pumping station:
easting value: 09° 51‘ 47.98“
northing value: 51° 20‘ 48.48“
above sea level: 135,6m
storage tank:
easting value: 09° 51‘ 53.65“
northing value: 51° 20‘ 46.12“
above sea level: 140,6m
Description of the extraction plant
The well has a depth of 5.00 m and a clear width of 2.00 m and was made by lowering concrete rings. The well head is located at 134.4 m.a.s.l. and is closed by a cast-iron round shaft cover of 60 cm diameter. The normal water depth is 3.00 m and drops to 1.00 m during heavy abstraction, corresponding to a water level of 2 m below the well head and a drawdown to 4 m below the well head. For water extraction, a pump house of corrugated metal construction with a transparent plastic roof is built on a concrete foundation (135.6 m.a.s.l.) at a distance of 5 m from the well. This houses a stationary pump unit consisting of a three-stage (Halberg Maschinenbau GmbH) high-pressure centrifugal pump with 2,900 rpm and a pumping capacity of up to 40m3 / hour, elastically coupled to a splash-proof AEG three-phase motor with an output of 18.9 kW for an operating voltage of 380 V. The pumping unit is of the same type as the pump house. Originally, there was the possibility of also pumping water through a windmill-driven rotating gear pump. The pump had a delivery head from the well's center water to the collection tank of 8.20 meters. Water was pumped to the collection tank at a maximum volume of 3-4 m³ per hour through a 5/4-inch pipe laid 1 m deep in the ground.
The water is pumped into a collection tank through a distribution shaft immediately adjacent to the pump house. In the distribution shaft, a water meter is installed in the pressure pipe. A lath gauge with centimeter divisions is installed in the collection tank where the water inflow and outflow can be checked. The clear width of the suction pipe (steel) is 90 mm. The suction height varies between 3.60 and 5.60m. Through a plastic pipe with a diameter of 80 mm and a length of 160 m, the irrigation water is pumped into a collection tank of dimensions 570 cm * 630 cm * 150cm (width * length * depth) with a capacity of about 50m3. The collection tank is located at the southern edge on the highest elevation of the irrigation area. The pumping height is 8.20 m from the average water level in the well (132.4 m.a.s.l.) to the highest level in the tank (140.60 m.a.s.l.). There are 2 underground hydrants in the pressure line to connect the irrigation lines.
From the collection tank, the irrigation water is fed to 8 terraced irrigation areas through a clay pipe with a diameter of 15 cm, which is laid 80 to 100 cm deep. The water reaches the irrigation areas through riser shafts of 60 cm clear width and 100 cm height. The flow to the areas is controlled by a gate valve with 150 mm passage and spindle guide on the collector tank. The size of the area that can be irrigated by the system is theoretically 5,384m2 in total.
Irrigation areas 7 and 8 have not been in operation since the 1980s and will not be irrigated in the future, as other experimental facilities and a machine shed have been built here. Therefore, the current irrigated area of the site in the sum of terraces 1 - 6 totals 3,709m2 (0.37 ha).
The 8 irrigation areas have the following sizes:
| Area | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|
| Area inm2 | 550 | 575 | 610 | 640 | 650 | 684 | 825 | 850 |
Information on the determination of the available water supply
From older records (Schumacher 1966) on the design of the water extraction system it can be seen that the existing well allows a withdrawal of 40m3 per hour, and that the water level in the well shaft drops by 2 m in the process. As part of the irrigation engineering exercises with students, the water yield of the well is also regularly noted. From these observations and handwritten notes, the following facts can be established: the water level in the well fluctuates by 3 m water level in the well shaft depending on the water level of the Werra. With the existing pump, the well is pumped empty in about 20 minutes, and then requires about 40 minutes to reach the original level in the well shaft again. There are holes in the lower concrete rings through which the water can flow. During a pumping test on May 17, 2013, the initial level in the well shaft was 277 cm (223 cm below the well head). With a pumping duration of 25 minutes, the water level dropped to 85 cm (415 cm below the well head). A level of 44 cm was reached in the collection tank. This corresponds to a pumping rate of 15.80m3 plus the amount of water in the pipeline (3.1415926 * 0.042 * 160 = 0.80m3), for a total of 16.60m3. This corresponds to a pumping capacity of 39.84m3/hour. Subsequently, water flowed into the well and the water level in the well rose by 100 cm in 17 minutes. This corresponds to an overflow of 3.14m3 (3.1415926 * 12) or 0.18m3 / minute. Regarding the hydrology, Hosch and co-workers made a study in 1994. The climatic water balance of the site is clearly positive; November through April is a distinct drainage period. Most of the irrigated land is outside the floodplain; only the lowest terrace is within the recent floodplain. The flood of 1909 reached 135.5 m above sea level. Profiles investigated by Hosch are about 0.8m (profile PG3) to 2.2m (profile PG 1) higher. Due to the accelerated deepening of the Werra after straightening measures in the 19th century, it can be assumed that the investigated profiles have not been flooded for about 150 - 200 years. Nevertheless, it is probable that the groundwater level still rises occasionally into the subsoil during simultaneous occurrence of Werra floods and lateral slope water inflow. During the study period (April-October) the groundwater level was lower than 2m, so that for the root zone of annual crops and grassland a capillary resupply from the groundwater during the vegetation period cannot be assumed. However, after summer precipitation, the underslope position allows lateral inflow of weakly stressed soil water (interflow) in backwater-conducting horizons (HOSCH et al. 1994).