Dams are like loaded guns

Dams are like

loaded guns

Water flowing over concrete spillway at Spioenkop Dam on the Tugela River

The Dam Safety Office (DSO), a division of the Department of Water and Sanitation (DWS), is responsible for safeguarding the people, properties and infrastructure downstream of dams. By Kirsten Kelly

Wally Ramokopa, director: Dam Safety Regulation, Department of Water and Sanitation

Like a loaded gun, a dam has the potential to cause serious harm. A loaded gun must never be left unattended, and must be owned by someone with a licence. Dams also require licences and only qualified people can design, build and assess them. One cannot own a dam without conducting regular assessments and maintenance,” explains Wally Ramokopa, director: Dam Safety Regulation, DWS.

Classification of dams A dam with a safety risk contains, or can store more than, 50 000 m³ of water and has a wall with a vertical height of more than 5 m. All dams with a safety risk, regardless of who owns them (public or private), must be registered with the DSO and comply with legislation.

Any structure capable of diverting or storing water is classified as a dam, and so the dam safety register also includes, for example, mine tailings dumps, pollution control dams, and potable water reservoirs that fit the classification. In exceptional cases, the Minister of the DWS may also declare a dam as having a safety risk even if it falls outside the

TABLE 1 Size classification of dams with a safety risk

Size

Small Medium Large

Maximum wall height

<12 m but <30 m 30 m

conventional registration parameters. Once the registration information of the dam is received, the DSO then classifies the dam into one of three categories that determine the required level of control at that particular dam. The classification is based on the size and hazard potential rating of a dam.

The hazard potential of a dam is based on an assessment of the potential loss of life, potential economic loss with respect to downstream development, as well as the potential adverse impact on resource quality that may result from the failure of a dam. Geographic information system (GIS) technology is used so that the DSO can see the position of any dam on a computer screen or on a 1:50 000 map and on satellite images in different years. Google Earth is also used. This helps the DSO assess a dam’s hazard potential by evaluating the households, property and infrastructure downstream that could be impacted should the dam fail.

The size of the dam and its hazard potential rating is used in allocating a category classification to the dam. “There are many instances where

TABLE 2 Hazard potential of dams with a safety risk

Hazard potential rating Potential loss of life

Low

None Significant ≤10 High >10

Potential economic loss

Minimal Significant Great

Potential adverse impact on resource quality

Low Significant Severe

The Gariep Dam has the highest storage capacity (5 343 m3) in South Africa

TABLE 3 Category classification of dams with a safety risk

Size Class Low Hazard potential rating

Significant High

Small Medium Large Category 1 Category 2 Category 2 Category 2 Category 2 Category 3 Category 3 Category 3 Category 3

these dams need to be reclassified. A dam that was built 70 years ago, for example, may not have had any people living or businesses operating downstream at the time, but this may have drastically changed over the years,” states Ramokopa.

Over 5 600 dams with a safety risk are registered with the DSO. They are owned by the DWS, other government departments (such as Agriculture and Correctional Services), farmers, mines, municipalities, water boards and individuals in their private capacity.

“The agricultural industry owns the most dams with a safety risk, while the DWS owns only 323 such dams (i.e. 6%); however, 87% of the storage capacity is in DWS-owned dams,” adds Ramokopa.

Approved professional persons Only approved professional persons (APPs) can perform certain dam safety tasks. These are professional engineers, technologists or technicians who are registered in terms of the Engineering Profession Act (No. 46 of 2000), and approved by the Minister of Water and Sanitation after consultation with the Engineering Council of South Africa and the DSO.

“APPs are people who are experienced and skilled in dam engineering. For Category 2 dams, all tasks must be carried out under supervision of an APP, whereas an APP must be assisted by a professional team of experts (such as mechanical engineers, hydrologists and geologists) for Category 3 dams. For Category 1 dams, the involvement of an APP is not required but the dam owner must fulfil the requirements of the dam safety regulations, which includes completing an official application form, submitting design reports and engineering drawings, and an evaluation of the safety of the existing development,” explains Ramokopa.

There is a register of APPs on the DWS website, which makes it easier for dam owners to find people with the necessary qualifications.

Ramokopa cautions that there is only a small list of APPs. “Currently, there are fewer than 100 APPs in South Africa (approximately 1 qualified person for every 50 dams on the Dam Safety register). More than 62% of these are older than 60 years of age.”

Licensing To perform any task at a safety risk dam (including construction, enlargement, alteration, repair or decommissioning), the owner needs to obtain a licence for construction from the DSO. This normally includes the completion of an application form accompanied by the required design reports and engineering drawings, as well as the

INTERESTING FACTS ON SA’s DAMS

• Oldest dam: Upper Mpate built near Dundee in 1880. It is an earthfill embankment with a height of 18 m and crest length of 293 m. • The big five dams are as follows:

Dam

Gariep Pongolapoort Sterkfontein

Height

88 89 93

Wall volume (million m3)

1.4 0.6 19.8

Storage capacity (million m3)

5 343 2 267 2 617

Water surface area (km2)

352 132 67

Vaal Vanderkloof 63 108 1.4 1.3 2 610 3 187 323 133

Over 5 600 dams with a safety risk are registered with the DSO. They are owned by the DWS, other government departments (like Agriculture and Correctional Services), farmers, mines, municipalities, water boards and individuals in their private capacity

TABLE 4 Dam safety evaluation scores

Symbol/score Analysis of condition from the recommendations and findings of a dam safety evaluation report by an APP

A

B

C

D

E

F Dam in good condition and routine maintenance acceptably up to date. An evaluation interval of longer than five years can be recommended (if the owner requests it or for farmers/smaller municipalities) Dam in reasonable condition but not complying to modern standards. Only routine maintenance and routine inspections recommended. An evaluation interval of longer than five years cannot be recommended Significant outstanding maintenance by normal operation and maintenance staff recommended, restoring dam to a functional state. Elementary monitoring systems like settlement beacons and flow monitoring included here Significant rehabilitation recommended to restore dam components to original state – e.g. repair major erosion or cavitations, repair slope protection, reinstate crest level, refurbish outlet works or gates. Work is considered significant rehabilitation if it is outside the capacity of the normal operation and maintenance staff, the appointment of a contractor is necessary, and the work should be done under guidance of an APP. Drafting of an operation and maintenance manual and/or emergency preparedness plan and install sophisticated monitoring instruments under guidance of an APP also included here Upgrading recommended – e.g. increase spillway capacity, increase freeboard, provide buttress/thicken dam to improve stability or install stress cables, install slope protection, install additional drainage or grouting or water seals to reduce leakage. A licence to alter and the services of an APP will be required Dam unsafe. Restrictions on operation recommended – e.g. water level may not exceed a specified level

evaluation of the safety of the existing development.

All new dams also require a wateruse licence for the water-use activity to store water, as well as an environmental authorisation.

“The licensing system has resulted in a significant improvement in the documentation of dam designs, as well as a significant improvement in the quality of professional persons involved in the process. As a result, the general safety of South African dams has also improved,” states Ramokopa. During the construction of a dam, quarterly reports must be submitted to the DSO and may be subjected to an in-person inspection. Once construction is completed (and before the dam is fully impounded), the owner of the dam must apply for a licence to impound. This involves the submission of an operation and maintenance manual and emergencypreparedness plan.

To reduce the risk of a dam failure, an APP is appointed to conduct a dam safety evaluation (DSE) on Category 2 and Category 3 dams every five to ten years.

The outcomes of DSEs determine the type of intervention/mechanism required to address any safety risks. These interventions/mechanisms could either be maintenance-related or capital-intensive where dam rehabilitation is required. Dams are then given a condition rating.

“The DSO then ensures that these directives are implemented within certain timeframes; however, it must be remembered that the owner has

The agricultural industry owns the most dams with a safety risk