Heritage Cases

PROPOSED STRUWIG DAM ,NDWEDWE LOCAL MUNICIPALITY

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THE PROPOSED STRUWIG AGRICULTURAL DAM LOCATED ON PORTIONS 9 & 10 ON THE FARM STRUWIG 15375, WARD 1, NDWEDWE LOCAL MUNICIPALITY (KZN 293), ILEMBE DISTRICT MUNICIPALITY

Expanded_Motivation: 

The proposed site is located in ward 1 of the Ndwedwe Local Municipality on portions 9 and 10 of 15375 of the Farm Langeboskop. The town of KwaDukuza is located 17 km to the south, and approximately 7km from the R74 main road from Stanger to Kranskop. The site is located within the U50A quaternary catchment, within the Little Nonoti Stream, a tributary of the Nonoti River. Water will primarily be sourced from the upstream catchment of approximately 17.6 km2. The average slope of the catchment is 15.7%. The site is located within an existing sugar cane agricultural farm. A portion of the farm will be transitioned t macadamia plantation which is also dependent on a steady supply of water in order to ensure viability. The dam site is located is at 29°13'23.49"S 31°13'42.47"E. The farm is surrounded by open sugar cane plantations and incised drainage valleys vegetated with indigenous forest. The farm is accessed by existing all weather and gravel roads. It is proposed that the dam wall will comprise material from deposits from the historic dam, as well as from commercial sources. Re-shaping and excavation within the dam inundation area will be required. The Struwig Groep (Pty) Ltd is submitting an environmental authorisation application for their proposal to construct a dam on their Farm portions 9 and 10 of the farm Langeboskop, to provide water for agricultural irrigation requirements. The proposed dam will acquire the same specifications as the pre-existing dam, thereby covering the same footprint. Water will be sourced from the Little Nonoti River that is collected by the dam wall. The dam will allow for environmental flows to continue throughout the construction an operational phases of the dam. Water from the dam will be used as supplementary supply to irrigate 100 hectares of macadamia plantation. Irrigation infrastructure will be installed from the dam. Drip irrigation will be utilised for the supplementary irrigation of macadamia plantations. The proposed dam is described as follows: • Dam Wall Height – 11.68m • Maximum full supply level depth – 11.10m • Surface Area – 2.8 Ha • Capacity – 113,000 m3 • Dam Wall Length – 80m • Dam Wall Width at foot of the dam – 60m • Dam Classification – Category 1 The proposed dam will comprise an earth embankment with a primary concrete side-channel spillway on the left flank of the dam wall. An emergency grassed by-wash spillway will be located on the right flank of the dam wall to discharge water during large flood events. The concrete spillway will measure 38.7m long and will have an available freeboard of 2.62m. The discharge at the available freeboard is 353m3/s. The emergency spillway will have a Safety Evaluation Discharge (SED) of 145m3/s. The emergency spillway on the right flank has a width of 54m. Earth material for the dam wall and emergency spillway will be sourced from within the floodplain of the Proposed Struwig Dam. Additional materials will be obtained from commercial sources. Excess soil material from the decommissioning of the historic dam wall and construction earthworks will be spoiled on the farm portions 9 and 10 Langeboskop. The spoils site is expected to cover an area of 1000m2. The anticipated construction sequence is as follows: • Construct earth canal to divert river past outlet pipe position • Clear foundation for outlet pipe and chambers • Construction of outlet pipe and inlet and outlet chambers • Divert the river via the outlet pipes by channelling it towards a coffer dam at the inlet chamber • Simultaneously to the above start with the extensions to the concrete spillway channel construction of spillway and tongue wall • Excavate to natural ground level • Commence construction of core trench and embankment • Commence emergency by wash spillway construction • Construct rip-rap • Topsoil and grass.

ApplicationDate: 

Friday, March 24, 2017 - 09:02

CaseID: 

10838

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