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United States Department of Agriculture

Agricultural Research Service

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1 - Wetland Reservoir Subirrigation System (WRSIS)
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3 - Page 3
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13 - Page 13


Van Wert County WRSIS site schematic

Local contractors completed Van Wert County WRSIS site construction in fall 1996 at a total capital cost of $86,300 U.S. This site has Hoytville clay (mesic Mollic Ochraqualfs) covering three 6.1 ha (15 acre) fields, two that are subirrigated, and one with buried pipe used for subsurface drainage only (fig. 5). From particle size analysis of samples taken at the surface, percent sand was 2% to 36%, silt ranged from 18% to 41%, and the amount of clay was between 47% and 56%. Saturated horizontal hydraulic conductivity values measured with a velocity permeameter ranged from 4 x 10-4 cm/s (0.6 in./hour) near the surface to 2 x 10-4 cm/s (0.3 in./hour) through the rest of the soil profile down to a depth of 1 m (3.3 ft).

As with all the WRSIS sites, subsurface drain pipes were installed at a nominal depth of 0.76 to 0.91 m (2.5 to 3 ft) beneath the surface. Drain lines within the two subirrigated fields have a spacing distance of 5.3 m (17.5 ft), and older 10 cm (4 in.) diameter clay tile pipe alternates with newer 10 cm (4 in.) diameter corrugated plastic tubing. The control plot has only the clay tile drain lines which are spaced 10.7 m (35 ft) apart. At the start, two hydraulic control structures, one for each subirrigated field, were installed to regulate shallow ground water levels. However, much like the Defiance County WRSIS site, a wet area in the north end of the east subirrigated field necessitated placement of an additional hydraulic control structure in June 1999. Consequently, the east subirrigated field is now partitioned into north and south zones for water table management purposes (fig. 5).

Initially, surface and subsurface drainage from all 18.2 ha (45 acres) of corn and soybean cropland were routed, via two 1.11 kW (1.5 hp) submersible pumps contained in a concrete sump, to a 0.79 ha (1.95 acre), 8710 m3 (2.3 million gal) capacity wetland and then a 1.21 ha (3.0 acre), 12870 m3 (3.4 million gal) capacity pond. In the summer of 2003, the wetland was converted to a wetland/reservoir complex comprised of a 0.36 ha (0.9 acre) wetland and a 0.85 ha (2.1 acre) reservoir. Within this complex, the wetland has a storage capacity of 3680 m3 (1 million gal), and the total reservoir storage capacity is 28330 m3 (7.5 million gal), of which 13550 m3 (3.6 million gal) can be drained by gravity. The wetland and reservoir are connected via a 30 cm (12 in.) diameter pipe with water flow regulated by a hydraulic control structure. A shallow earth embankment extending out into the wetland from its southeast corner increases the residence time of water flowing from the inlet to the outlet. By doing this, wetland effectiveness for water treatment is improved. The sump is located directly south between the wetland/reservoir complex and the pond. A 0.75 kW (1 hp) submersible pump, also located in the concrete sump, is used for subirrigation. Besides the wetland/reservoir complex and the pond, a ground water well located at the site can also supply water for subirrigation.

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Last Modified: 8/13/2016
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