Belize's Polluted Macal River

The Macal River in Belize is a vital source of drinking water and other domestic uses for the populations living along it. However, the river has been facing several issues, primarily concerning water quality degradation due to extensive deforestation, unsustainable agricultural practices, and traditional slash-and-burn techniques. The river, which runs through the Cayo District in western Belize, is known for its ancient Mayan history and its role in connecting urban, trade, and ceremonial centres. It is a popular spot for canoeing and kayaking and wildlife encounters, with various animals and birds along its banks.

The Macal River is prone to flooding

The Macal River's susceptibility to flooding is further exacerbated by the geometry of its lower basin tributaries. These tributaries, including the Privassion, Rio On, Rio Frio, Mollejon, Chaa Creek, and Cacao Camp, are arranged radially, causing all sub-basin flow to reach the mainstem nearly simultaneously. This simultaneous peak flow creates a massive peak wave that worsens downstream flooding in the Belize River and controls the flood stage of the larger river.

The Macal River's flooding has been studied by the Caribbean Disaster Mitigation Project (CDMP) in collaboration with the Government of Belize. Their investigations have contributed to the development of a flood-hazard model for the Belize River to improve flood-hazard awareness and response. The most severe floods on the Belize River can be traced to the Macal River, particularly during wet periods when rainstorms in the Maya Mountains cause sudden flood waves. These waves are so large and abrupt that they not only flood the main channel of the Belize River but also flow upstream into other tributaries.

The Macal River's role in flooding was also recognised historically. During the early days of European arrival, the river was essential for floating logs downstream to the coast, and the early settlers relied on the Macal for transportation and survival. Even when the Western Highway was an often impassable dirt track, the Macal remained the lifeline for San Ignacio Town and the surrounding settlements and farms.

The river's steep terrain and high rainfall contribute to flooding

The Macal River in Belize is prone to flooding, and this is largely due to its steep terrain and high rainfall. The river rises in the rugged Maya Mountains, an area of high rainfall, and flows north, joining with the Mopan River to form the Belize River. The steep terrain of the headwaters region, combined with the high rainfall in the upper basin, causes the Macal River to rise rapidly, contributing to downstream flooding of the Belize River.

The Macal Rivershed is divided into two sub-catchment basins. The headwaters and upper basin, covering about 1000 square kilometers, lie in the southern Maya Mountains. The lower basin, known as the Mountain Pine Ridge catchment, has a different topography. The upper basin has shallow and rocky soils that lead to rapid runoff, while the lower basin has denser terrain that causes friction and slows down surface runoff.

During wet periods, rainstorms in the Maya Mountains can cause sudden flood waves on the Macal River. These waves are so large and rapid that they not only flood the main channel of the Belize River but also flow upstream into other tributaries. The configuration of the Mountain Pine Ridge catchment plays a crucial role in this process. The tributary streams in this area are arranged radially around the main channel, causing a rapid increase in river flow after rainfall. In contrast, the southern area of the Maya Mountains has longer channels that join at longer intervals, resulting in a more gradual flow.

The interaction between these two distinct sections of the Macal watershed contributes significantly to the downstream flooding. The rapid runoff from the Mountain Pine Ridge catchment combines with the accelerating flow from the southern Maya Mountains, forming a single massive peak wave. This effect is further enhanced by the radial geometry of the lower basin tributaries, causing all the sub-basin flow to reach the main channel simultaneously. As a result, the Macal River experiences rapid stage height rises, exacerbating downstream flooding in the Belize River.

The steep terrain and high rainfall in the Macal River's upper basin significantly influence the river's behavior and contribute to the frequent and severe flooding downstream. The unique characteristics of the two sub-catchment basins, including their topography and hydrology, play a crucial role in shaping the flooding patterns. Understanding these factors is essential for effective flood management and the protection of the surrounding areas.

The river's flow is modelled to understand and manage flooding

The Macal River in Belize is prone to flooding, which has a significant impact on the lives and livelihoods of Belizeans. The river's flow has been modelled to better understand and manage this flooding.

The Caribbean Disaster Mitigation Project (CDMP), in collaboration with the Government of Belize, has developed a flood-hazard model for the Belize River, which is fed by the Macal River. This model aims to aid flood-hazard awareness and response. The Macal River is one of the two main tributaries of the Belize River system and is responsible for the most severe floods. During wet periods, rainstorms in the Maya Mountains can cause sudden and extreme flood waves that not only flood the main channel of the Belize River but also flow upstream into other tributaries.

The model for the Belize River was developed in three phases, each providing unique insights into the nature of the Macal watershed. The first phase treated the watershed as a three-dimensional surface with uniform resistance to surface flow. This analysis revealed that the Macal watershed consists of two distinct sections: the northern area, Mountain Pine Ridge, and the southern area, the middle of the Maya Mountains. The second phase involved adding maps of friction factors, which represent rough flow overland and smoother flow in channel areas. This refinement showed how the storm flow from the southern section accelerates and merges with the runoff from Mountain Pine Ridge, resulting in a large flood wave. In the third phase, the model was tested with varied rainfall patterns, including prolonged standard rainfall and historical rain storms.

The model identified several critical factors contributing to the flooding problem:

• The configuration of the Macal watershed, with two main divisions linked in series, causes the runoff from the upper watershed to accelerate and merge with the flow from Mountain Pine Ridge, forming a single large flood wave.
• The friction resistance to fluid flow is generally high across the watershed due to dense ground cover, which acts to retard the runoff.
• The soils in the mountains are shallow and rocky, allowing water to infiltrate quickly and contributing to rapid runoff.
• The proximity of the Macal River to the mountains results in short response times, with heavy rains on unsaturated soils turning into channel flow within about a week.

To address the flooding problem, the model suggests a combination of active measures and good land management practices:

• An impoundment at the upper Macal River where it passes through the ridge above Guacamayo could help retard the second flood wave. However, this would require careful design, management, and adequate funding.
• Good land management practices, such as limiting the size of timber clear-cuts and maintaining buffer zones around channels, can help protect the friction effect that mitigates flood waves.

Fluvial modelling is a process that simulates the flow of water in a river and its floodplain using a computer program. It provides predictions about the river's behaviour under different conditions. In the context of the Macal River, fluvial modelling can be used for flood hazard mapping, river structure design, real-time flood warning, drainage design, and flood risk assessments.

The river is a source of drinking water but water quality is poor

The Macal River in Belize is a vital source of drinking water for the populations living along the river. However, the river's water quality is poor due to several factors. Firstly, extensive deforestation in the upper reaches of the Mopan River, a tributary of the Macal River, has led to increased sedimentation and nutrient loading in the water. This, combined with runoff from unsustainable agricultural practices, has resulted in higher levels of toxins, including pesticides, in the water. Traditional slash-and-burn agricultural methods have also contributed to the degradation of the river's water quality.

The construction of the Chalillo Hydroelectric Dam on the Macal River has further exacerbated the issue. Environmentalists have expressed concern over the release of toxic water from the dam, with high levels of turbidity caused by both organic and inorganic dissolved and suspended materials in the reservoir. The high turbidity protects waterborne microbes such as bacteria, viruses, and protozoa, making the water unsafe for drinking. Additionally, the materials causing turbidity can clog filtration systems used to pre-treat drinking water, further compromising its potability.

The geological makeup of the Maya Mountains, through which the Macal River flows, also contributes to the poor water quality. The mountains are composed of materials that break down into large amounts of clays, silt, sand, and pebbles during the tropical weathering process, leading to increased sedimentation in the river.

The poor water quality of the Macal River is a significant concern as it directly or indirectly supplies water to one-third of Belize's population. While the Belize Electric Company Limited (BECOL) has downplayed the issue, asserting that the water contains only harmless silt, water quality experts disagree and have warned against consuming the water.

Deforestation and unsustainable agriculture are major sources of river degradation

The leading cause of deforestation is agriculture, with poorly planned infrastructure being another significant contributor. Every year, the world loses around 5 million hectares of forest, 95% of which occurs in the tropics. At least three-quarters of this is driven by agriculture—clearing forests to grow crops, raise livestock, and produce products like paper.

The Macal River in Belize is a prime example of the impacts of deforestation and unsustainable agriculture on river health. The river flows through the Cayo District in western Belize and is prone to severe flooding. The construction of the Chalillo Hydroelectric Dam on the Macal River in 2005 generated controversy over its effect on the surrounding rainforest.

Deforestation in the Macal River Basin can have several negative consequences for the river and the surrounding ecosystem:

• Reduced Infiltration and Increased Runoff: Trees normally soak up rainwater through their roots, allowing it to infiltrate the soil. Deforestation leads to decreased infiltration and higher amounts of surface runoff, increasing the risk of flooding.
• Soil Erosion: Without trees to anchor the soil, erosion rates can increase, causing soil to wash away into rivers. This can result in higher levels of sedimentation in the river and decreased water quality.
• Altered Water Cycles: Trees play a crucial role in the water cycle by absorbing water from the soil and releasing it through transpiration. Deforestation disrupts this process, leading to reduced moisture in the air and changes in precipitation patterns, potentially impacting the river's water flow.
• Loss of Biodiversity: Deforestation can result in the loss of habitat for numerous plant and animal species, including rare and endangered species such as the jaguar and Baird's tapir, found in the Macal River Basin.
• Increased Greenhouse Gas Emissions: Forests act as carbon sinks, absorbing carbon dioxide from the atmosphere. When forests are cut down, they release stored carbon, contributing to climate change and potentially altering local weather patterns.

Unsustainable agricultural practices, such as the overuse of pesticides and fertilisers, can also have detrimental effects on river health. These practices can lead to increased chemical runoff into rivers, polluting water sources and harming aquatic life. Additionally, unsustainable agriculture can contribute to soil erosion and reduce water quality.

To mitigate the impacts of deforestation and unsustainable agriculture on the Macal River, sustainable land management practices must be implemented. This includes promoting reforestation, adopting agroforestry techniques, and implementing conservation measures to protect critical habitats. Additionally, collaboration between government, local communities, and other stakeholders is essential to address the issue effectively.

Frequently asked questions