WDP4801 Assignment 01 2026 Due 10 May 2026

University of South Africa
College of Science, Engineering and Technology

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WDP4801
Water Development and Planning
Dam Feasibility, Design and Construction
Assignment 1 — 2026
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Module Code: WDP4801

Module Name: Water Development and Planning

Assignment: Assignment 1

Year: 2026

Total Marks: 100

Institution: University of South Africa (UNISA)

Department: Civil and Environmental Engineering




Submitted in partial fulfilment of the requirements for WDP4801 — UNISA, 2026

,UNISA | WDP4801 Water Development and Planning



Contents

1 Question 1 [15 marks] 4
1.1 (a) Briefly explain the primary and secondary purposes of the proposed dam in the
South African context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.1 Primary Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.2 Secondary Purposes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 (b) Justify why a dam is preferred over alternatives such as groundwater abstrac-
tion, water reuse, or desalination . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.1 Versus Groundwater Abstraction . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.2 Versus Water Reuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.3 Versus Desalination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2 Question 2 [20 marks] 8
2.1 (a) Identify and discuss five key site selection criteria for dam construction . . . . 8
2.1.1 1. Topography and Valley Shape . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.2 2. Geology and Foundation Conditions . . . . . . . . . . . . . . . . . . . . 8
2.1.3 3. Catchment Area and Hydrology . . . . . . . . . . . . . . . . . . . . . . 9
2.1.4 4. Availability of Construction Materials . . . . . . . . . . . . . . . . . . . 9
2.1.5 5. Environmental and Social Considerations . . . . . . . . . . . . . . . . . 9
2.2 (b) Explain how valley shape and topography influence storage capacity, dam type,
and construction cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.1 Conceptual Description of Valley Shapes . . . . . . . . . . . . . . . . . . . 11
2.2.2 Effect on Storage Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.3 Effect on Dam Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.4 Effect on Construction Cost . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3 Question 3 [20 marks] 13
3.1 (a) Describe the geological and geotechnical investigations required before dam con-
struction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1.1 Desk Study and Remote Sensing . . . . . . . . . . . . . . . . . . . . . . . 13
3.1.2 Engineering Geological Mapping . . . . . . . . . . . . . . . . . . . . . . . 13
3.1.3 Borehole Drilling and Sampling . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1.4 In-Situ Permeability Testing . . . . . . . . . . . . . . . . . . . . . . . . . . 14


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,UNISA | WDP4801 Water Development and Planning


3.1.5 Laboratory Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1.6 Seismic Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2 (b) Explain how foundation conditions influence the choice between earthfill dam,
rockfill dam, and concrete gravity dam . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.1 Earthfill Dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.2 Rockfill Dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.3 Concrete Gravity Dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4 Question 4 [25 marks] 17
4.1 (a) Explain the importance of Mean Annual Runoff (MAR) in reservoir sizing . . 17
4.1.1 Why MAR Is Central to Reservoir Sizing . . . . . . . . . . . . . . . . . . 17
4.1.2 The MAR-Storage-Yield Relationship . . . . . . . . . . . . . . . . . . . . 17
4.2 (b) Discuss the impact of evaporation, sedimentation, and assurance of supply on
dam capacity and yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.2.1 Evaporation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.2.2 Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.2.3 Assurance of Supply: 95% vs 99% . . . . . . . . . . . . . . . . . . . . . . 20

5 Question 5 [20 marks] 22
5.1 (a) Identify the major cost components of dam construction . . . . . . . . . . . . 22
5.2 (b) Discuss three major risks associated with dam development in South Africa and
propose mitigation measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.2.1 Risk 1: Internal Erosion and Piping Failure . . . . . . . . . . . . . . . . . 24
5.2.2 Risk 2: Inadequate Spillway Capacity and Overtopping . . . . . . . . . . 24
5.2.3 Risk 3: Cost Overrun and Funding Risk . . . . . . . . . . . . . . . . . . . 25

Reference List 26




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Question 1 [15 marks]

Your local municipality is considering the construction of a small to medium-sized earthfill dam
to augment water supply for domestic use and emerging irrigation schemes. You have been
appointed as an engineering technologist to conduct a preliminary feasibility study.


(a) Briefly explain the primary and secondary purposes of the proposed dam in the
South African context

Primary Purpose

The primary purpose of the proposed earthfill dam is water supply augmentation for do-
mestic use. In the South African context, this means providing a reliable, impounded surface
water source to supplement municipal water supply systems, particularly in semi-arid or water-
stressed areas where groundwater is insufficient or unreliable (Van der Merwe et al., 2020).

Specifically, the primary purposes include:

• Domestic water supply: The dam will store surface runoff collected during rainy seasons
to provide a continuous water source for household consumption. In many South African
municipalities, seasonal rivers and streams provide the only meaningful runoff, making stor-
age dams essential infrastructure.

• Water security: By creating a multi-year storage reserve, the dam allows the municipal-
ity to bridge periods of drought or low river flow, which are increasingly frequent in South
Africa’s variable climate (DWAF, 2013).


Secondary Purposes

Beyond the primary water supply function, the proposed dam serves several secondary pur-
poses that increase the overall value of the infrastructure investment:

• Irrigation for emerging farmers: The stored water can be released in a controlled man-
ner to support emerging irrigation schemes in the surrounding area, contributing to agricul-
tural development and food security in line with national development objectives.

• Flood attenuation: An earthfill dam with an appropriate freeboard and spillway design
attenuates downstream flood peaks by retaining excess runoff during storm events, reducing


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