Black River Impoundment - Project 176



Project Location

The Black River Impoundment project (RLWD Project 176) is located in section 3 and 4 of Polk Centre Township in Pennington County. It is approximately 9 miles west of the City of St. Hilaire and resides on the southerly property immediately adjacent to Pennington County State Aid Highway 3, just east of the Black River.

Design Considerations

The primary purpose for the project is to reduce flood damages within the Black River sub-watershed. An off-channel flood control impoundment will be constructed to store floodwaters from the approximate 16.9 square mile drainage area and strategically release the floodwater when downstream channel conditions can accommodate them. The impoundment will be maintained in a dry condition when flooding is not occurring. The impoundment will have a total capacity of approximately 4,064 acre-feet (4.51 inches), of which 3,162 acre-feet will be gated providing detention time of approximately 33 days if needed.

Looking North From South West Corner of Embankment

Project Components

The diking system will consist of the main impoundment around the north, south, and west sides of thesite, tying into natural ground on the east end. The main dike will consist of approximately 3.0 miles of dike around the impoundment. The dike along the west side will be the highest approaching a maximum of 14 feet with an average of 8 to 12 feet above natural ground. The dikes along the north and south sides will be highest at the west end, about 10 to 12 feet. A typical section having a 12-foot top and 4:1 exterior side slope and 5:1 interior side slope will be used for the diking system. To maximize the drainage area and direct runoff into the site, the project proposes 3 diversion ditches to be constructed. A 2.5-mile diversion ditch will be constructed in a north-south direction along CR 68. The proposed diversion ditch will begin at the half mile line in Section 24, T153N, R45W and flow in a southerly direction along the east side of CR 68 for approximately 1.5 miles, then crossing over to the west side of CR 68 in the northeast corner of Section 35, T153N, R45W until intersecting with Judicial Ditch (JD) 25-3 and flowing west 0.4 miles, crossing CR 3 to the impoundment site. The second 5.5-mile diversion ditch will be constructed beginning at the upstream end along the east side of CSAH 12 in the northeast corner of Section 18, T153N, R44W and flowing in a southerly direction along the east side of CSAH 12 for approximately 3.8 miles, then crossing over to the west side of CSAH 12 into Section 36 T153N, R45W, then proceeding south approximately 0.2 miles until intersecting with JD 25-3, then flowing west 1.0 miles along the north side of CSAH 3 in JD 25-3 to the location where the 2.5 mile diversion ditch along CR 68 enters into JD 25-3. The third 3.7-mile diversion ditch will begin at the upstream end 0.3 miles west of the southeast corner of Section 5, T152N, R44W, and flow in a westerly direction up to the Black River Church property in the southwest quarter of the southwest quarter, Section 2, T152N, R45W and flows north then west along the church property line before crossing CR 67 and entering the impoundment site in Section 3, T152N, R45W.

STA 63+00 Looking North

The water from the diversion ditches will navigate through the impoundment site by constructing inlet channels along the interior of the dikes in Section 3 and 4, T152N, R45W to the outlet in the southwest corner of the storage facility.

The proposed outlet of the impoundment site will be a gated culvert and riser and an auxiliary spillway for extreme flows. The low flow outlet is sized so that at least 85% of the gated volume will be released in 10 days or less. The auxiliary spillway (emergency spillway) is sized to protect the embankment from overtopping and is proposed to be cut through natural ground on the east end of the south embankment.

The Black River Impoundment Project was awarded to R.J. Zavoral & Sons, Inc. and work began in the late fall of 2020.

Functional Design Data

Feature
Measurement
Storage (acre-ft.)
Top of Dam (Total Storage) 1023.5 Ft. msl 4,064 (4.51 in. runoff)
Secondary Spillway 1020.50 Ft. msl --
Ungated Storage to Emergency Spillway -- 902 (1.00 in. runoff)
Gated Storage -- 3,162 (3.51 in. runoff)
Drainage Area 16.9 Sq. Mile --