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
Corridor: 12
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 system

The well has a depth of 5.00 m and a clear width of 2.00 m and was constructed by lowering concrete rings. The well head lies at 134.4 m above sea level and is closed by a round cast-iron shaft cover with a diameter of 60 cm. The normal water depth is 3.00 m and drops to 1.00 m during heavy abstraction, which corresponds to a water level of 2 m below the well head and a lowering to 4 m below the well head. A pump house in corrugated sheet metal construction with a transparent plastic roof on a concrete foundation (135.6 m above sea level) has been erected 5 m away from the well for water extraction. It houses a stationary pump unit, consisting of a three-stage (Halberg Maschinenbau GmbH) high-pressure centrifugal pump with 2,900 rpm and a delivery rate of up to 40^m3 / hour, flexibly coupled with a splash-proof AEG three-phase motor with an output of 18.9 kW for an operating voltage of 380 V. Originally, it was also possible to pump water using a windmill-driven rotating gear pump. The pump had a delivery head of 8.20 m from the middle of the well to the collection tank. Water with a maximum volume of 3-4 m³ per hour was pumped into the collection tank through a 5/4 inch pipe laid 1 m deep into the ground.

The water is pumped into a collection tank via a distribution shaft directly next to the pump house. A water meter is installed in the pressure line in the distribution shaft. A slatted level with centimeter graduations is installed in the collection tank, which can be used to check the water inflow and outflow. The clear width of the suction pipe (steel) is 90 mm. The suction height varies between 3.60 and 5.60 m. The irrigation water is pumped through a plastic pipe with a diameter of 80 mm and a length of 160 m into a collection tank measuring 570 cm * 630 cm * 150 cm (width * length * depth) with a capacity of approx. 50^m3. The collection tank is located at the southern edge on the highest elevation of the irrigation area. The delivery head is 8.20 m from the average water level in the well (132.4 m.a.s.l.) to the maximum level in the tank (140.60 m.a.s.l.). There are 2 underground hydrants in the pressure line for connecting the irrigation pipes.

Inspection chamber with counter and measuring device

The irrigation water is fed from the collection tank through a clay pipe with a diameter of 15 cm, which is laid 80 to 100 cm deep, to 8 terraced irrigation areas. The water reaches the irrigation areas through riser shafts 60 cm wide and 100 cm high. The inflow to the areas is regulated via a gate valve with a 150 mm passage and spindle guide on the collection tank. The area that can theoretically be irrigated by the system is 5,384^m2 in total.

Irrigation areas 7 and 8 have not been in operation since the 1980s and will no longer be irrigated in the future, as other experimental facilities and a machine shed have been built here. The current irrigation area of the site therefore amounts to a total of 3,709^m2 (0.37 ha) in the sum of terraces 1 - 6.

The 8 irrigation areas have the following sizes:

Area	1	2	3	4	5	6	7	8
Area in^m2	550	575	610	640	650	684	825	850

Information on determining the available water supply

Older records (Schumacher 1966) on the design of the water extraction system show that the existing well allows a withdrawal of 40^m3 per hour and that the water level in the well shaft drops by 2 m in the process. As part of the irrigation technology exercises with students, the water supply of the well is also regularly determined. The following facts can be determined from these observations and handwritten notes: the water level in the well fluctuates by 3 m depending on the water level of the Werra. With the existing pump, the well is pumped empty in approx. 20 minutes and then takes approx. 40 minutes to return to the original water level in the well shaft. There are holes in the lower concrete rings through which the water can flow. During a pumping test on 17.05.2013, the initial level in the well shaft was 277 cm (223 cm below the well head). After 25 minutes of pumping, the water level dropped to 85 cm (415 cm below the well head). A water level of 44 cm was reached in the collection tank. This corresponds to a flow rate of 15.80^m3 plus the amount of water in the pipe (3.1415926 * 0.042 * 160 = 0.80^m3), i.e. a total of 16.60^m3. This corresponds to a pump output of 39.84^m3/hour. Water then flowed into the well and the water level in the shaft rose by 100 cm in 17 minutes. This corresponds to a run-on of 3.14^m3 (3.1415926 * 12) or 0.18^m3 / minute. Hosch and his colleagues carried out a study on the hydrology in 1994. The climatic water balance of the site is clearly positive, November to April is a pronounced drainage period. Most of the irrigation areas are outside the flood zone, only the lowest terrace is part of the recent floodplain. The flood of 1909 reached 135.5 m above sea level. Profiles investigated by Hosch are approx. 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 around 150 - 200 years. Nevertheless, it is probable that the groundwater level still occasionally rises into the subsoil when Werra floods and lateral slope water inflow occur simultaneously. During the study period (April-October), the groundwater table was deeper than 2 m, so that capillary replenishment from the groundwater during the vegetation period cannot be assumed for the root zone of annual crops and grassland. However, after summer precipitation, the position of the lower slope allows the lateral inflow of weakly stressed soil water (interflow) in waterlogged horizons (HOSCH et al. 1994).