Prevention and mitigation of accidents in civil engineering

Flooding is the most destructive natural threat in Pakistan, and the recent flooding has demonstrated its seriousness. Floods are common throughout the country, but their characteristics differ from region to region. This article examines the flood behavior of major basins and flood management at the national level. Monsoon rains are the main source of flooding in the Indus Basin, while Mediterranean waves and cyclones that are generated over the Arabian Sea cause flooding in the Haran Basin and the Makran coastal zone.

River floods in the Indus basin have resulted in severe economic losses.

The Pakistani government has spent enormous resources on relief operations and floods since the country’s inception in 1947. A number of provincial and federal laws, ordinances, agreements and treaties form the national flood policy. The institutional framework for flood and crisis risk management has evolved over the years. However, the data does not show a significant decrease in the flood-to-damage ratio. The relationship between structural and non-structural measures and their combined effectiveness must be analyzed and optimized for more effective flood management.

Introduction

In August 2010, Pakistan suffered one of the worst floods in its history. Floods are the most frequent and destructive natural disasters in the country. Of the total population affected by natural disasters, 90% are affected by floods (Haider, 2006). The recent flood has killed nearly 1,800 people and cost tens of billions of dollars in financial losses. According to available official statistics, from independence in 1947 to the 2010 floods, according to available official statistics, about 8,000 people lost their lives and economic losses amounted to about $ 10 billion.

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River floods in the Indus basin

The total catchment area of ​​the Indus is 944,000, 60% of which is in Pakistan (MoE, 2003). The average annual flow of the Indus, with its main tributaries, the Jelum, Chenab, Sutlej and Ravi, is 175 per year. Table 1 provides an overview of the main rivers of the Indus Basin. Fluxes from time to time range from 3000 to 34000 / s (FFC, 2009). The annual river runoff at the marginal stations (the first gauging station after the river flows into Pakistan) ranges from 120 to 230 km3 / year (MoWP, 2002b). Rainfall in the Indus Basin occurs during the rainy and cold seasons, but severe floods only occur during the rainy season.

Flood reasons

Flooding in rivers is usually caused by heavy, concentrated rainfall in catchments during the rainy season, sometimes exacerbated by snow melt streams. Monsoon currents originating in the Bay of Bengal and resulting from depression often cause heavy rainfall in the foothills of the Himalayas. They are further influenced by weather systems from the Arabian Sea (due to seasonal lows) and from the Mediterranean Sea (via westerly waves), which sometimes cause devastating flooding in one or more of them. the main rivers of the Indus system.

However, extremely severe floods have sometimes been caused by the formation of temporary natural dams by landslides or glacier movements and their subsequent collapse. These are large seasonal fluctuations in almost all river flows, which further worsen the flow and morphology of the river.

Prevention

Mitigation and prevention are often used synonymously and can be defined as structural or non-structural measures taken to limit or reduce the adverse effects of natural disasters such as floods, earthquakes, etc.

Plan

The following structural and non-structural measures can be taken to ensure flood mitigation in Pakistan over the next 15 years.

Structural measures:

1. Dam construction: Dams are structures built on a river to store water and, in an emergency, can accumulate excess water so that discharge downstream of the dam can be controlled. The water level in the tanks can be lowered before it rains by opening the weir so that more water can be stored in the tanks and drained later. Pakistan currently has 150 larger dams that are over 15 meters high. Some of these dams are not operational. A national consensus is needed to ensure that all dams are operational so that in the event of rain, excess water can be stored in the dams.
2. Building codes: In Pakistan, building codes are rarely used for construction in certain areas. One of the generally accepted building codes that can be used is ASCE 24-05 – Flood Resistant Design and Construction. In addition, the ground floor fence must be higher than the base flood level. The use of porous coatings and vegetable buffers should be encouraged.
3. Settling ponds and outfalls: Settling ponds can also be built in flood-prone areas so that water can be stored and discharged later.
4. Stormwater Sewers: The drainage system for collecting stormwater in Pakistan is ineffective. Although there is a drainage system in large cities, in small towns and villages it is either in poor condition or completely absent. Light rain can cause overflow and flooding. Stormwater drainage should be modified as it can allow stormwater or stormwater runoff to be quickly transferred to the main drain, thus preventing local flooding.
5. Maintenance work: The most important step is to ensure the maintenance of existing or newly built structures. The construction of a structure on a river or canal is very common in the country, but no maintenance work is carried out to ensure smooth operation. As a result, the structure becomes non-functional long before its useful life, and the desired goal cannot be achieved.

Non-structural measures:

1. Flood Forecasting System: The first step that can be taken to mitigate the effects of floods is the implementation of an effective and efficient flood forecasting system in Pakistan. Floods can be mapped and modeled to determine the extent of possible flooding. Mostly floods are caused by heavy rainfall, snowfall, etc., and research into these two factors can help mitigate or circumvent the impact of floods.
2. Floodplain population: Population density and development in floodplains should be limited. This can be done by providing incentives or other benefits.
3. Channeling: In Pakistan, there is a trend towards channel modification, which is commonly known as channeling. Farmers and wealthy people often pay money to change the canal to suit their needs, namely the watering of their crops. Usually canals are built taking into account the flow of the river. An organizational unit should be created within the already operational Pakistan Irrigation Department to manage these canal modifications. Keep in mind that the concrete lining should be done on the canals, as friction will be reduced, allowing the discharge to pass easily through the canals and the channel cross-section should not be reduced as this will reduce the flow through the river.
4. Flood management plan: To mitigate the effects of floods, a flood management plan for urban and rural areas needs to be developed. The committee can be formed from government officials and local residents. The aim should be to raise awareness of the necessary preventive measures, for example, if there is a need to build a storm drain or any other structure, the local population should inform the official who, in turn, will take steps to comply with the requirement.
5. Funds management: In Pakistan, departmental management is a major issue. There are many agencies, such as the Federal Flood Commission (FFC), to ensure safety. This institute had a lot of funds available to design structures that can control flooding, but the practical work is practically nil. Only if this corruption or audit of such institutions can be carried out, disasters such as floods can be significantly reduced.
6. Floodplain population: Population density and development in floodplains should be limited. This can be done by providing incentives or other benefits.
7. Public Awareness: There should be some kind of programs that raise public awareness of the dangers of flooding. They must be trained in the protective measures necessary to protect themselves and the lives of those around them. At the school level, basic evacuation exercises should be taught, which can be very helpful during floods.

References

1. Farhan Sami and Saira Shafi, “Reviewing Critical Issues Associated with the Kalabag Dam to Analyze Positive and Negative Scenarios and Develop Country Recommendations,” MA in Environmental Sciences, Kinniard College, Lahore, September 2001.
2. Federal Flood Commission, Annual Flood Report 2001, February 2002.
3. dr. Bashir Chandio and Ms. Nuzhat Yasmin, “Proceedings of the National Workshop on Water Achievements and Challenges in the 20th Century and the Challenges of the Next Millennium,” Pakistan Water Research Council, June 1999.
4. Center of Excellence in Water Engineering, Lahore, Proceedings – Water for the 21st Century: Supply, Demand, Development and Socio-Environmental Issues, June 1997.