BECOL releases additional information on operations on Macal River

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The Belize Electric Company Limited (BECOL) has released additional information on its operations on the Macal River. Due to COVID-19, BECOL has been unable to hold public consultations as it would customarily do. In a most recent information release, BECOL addresses the environmental impacts of the dam as well as its preparedness in the event of a dam breach.
Dam activity can have a direct effect on dissolved oxygen, temperature, and total suspended solids. Those parameters can, in turn, influence the behaviour of others which can affect the entire river system. There is also the potential for the accumulation of substances over time, which could be released during instances of spillage or flushing. This could include substances such as nutrients or bacteria that are non-hazardous in low concentrations but hazardous in high.
BECOL operates three dams in the Macal River Basin. The Chalillo Hydroelectric Facility is located on the Macal River in the Cayo District, in western Belize. The facility site is 12 miles (19.3km) upstream from the Mollejon Hydroelectric Facility, 30 miles (48.3km) from Cristo Rey Village, and 32 miles (51.5km) from the twin towns of San Ignacio and Santa Elena. Cristo Rey is the nearest community along the river to the facility site. The Chalillo Hydroelectric Facility is designed to generate 7.0 megawatts of power. Additionally, the Mollejon Hydroelectric Facility is 12 miles (19.3km) downstream of the Chalillo Hydroelectric Facility, 18 miles (30km) from Cristo Rey Village, and 20 miles (32.2km) from the twin towns of San Ignacio and Santa Elena. While the Vaca Hydroelectric Facility is three miles downstream from the Mollejon Hydroelectric Facility, 15 miles from Cristo Rey Village, and 17 miles from the twin towns of San Ignacio and Santa Elena.
The Belize Electric Company Limited (BECOL), as a part of its signed Environmental Compliance Plan and its wider corporate commitment to providing electrical power to its consumers in an environmentally responsible manner, conduct regular water quality and sediment monitoring along the Macal River Basin. This includes headwaters, Chalillo Dam area, Mollejon Dam area, Vaca Dam area, and downstream areas near established communities. The purpose of this monitoring is to determine the effect of the dam activities on the environment in order to inform BECOL’s decision-making process and to ensure the fulfilment of its environmental commitments. As a result, BECOL has contracted the services of the Coastal Zone Management Authority and Institute (CZMAI) to conduct Water Quality and Sediment Monitoring on their behalf. The following report focuses on the findings of the Quarter 4 (October 2020) sampling campaign.
The CZMAI Water Quality Monitoring Unit carried out a water and sediment quality monitoring campaign from September 28 to October 7, 2020. The unit collected a total of twenty-three (23) water samples and seven (7) sediment samples along the Macal River to be tested for various parameters identified by BECOL and the Department of Environment.
As we reviewed in the Guardian Newspaper last week, analysis of data for Quarter 4 (October) 2020 showed that the Macal River Basin is in an overall healthy condition. In general, all the parameters measured were well within the range of values you find in healthy rivers using the United States Environmental Protection Agency standards. There were very few outliers identified; however, their effects did not influence the water quality in the downstream areas. Therefore, from the data collected there is no risk to downstream communities as a result of the hydroelectric dam activity along the river during this sample period.
Nitrate and phosphate concentrations for Q4 were low throughout the Macal River Basin, however, when compared to values for the previous sample periods (June and August 2020). This general trend of lower levels was prevalent for most parameters measured during this sample period. Total Coliform and E. coli concentrations in October 2020 was low overall throughout the Macal River Basin. There were measurements that exceeded the upper limit thresholds of 5000 CFU/100mL and 200 CFU/100mL respectively.
The downstream areas consist of three sample sites, one in Cristo Rey and two near San Ignacio Town. These sites were strategically chosen since they are the major population centers downstream from dam activity. Therefore, it is important to determine if dam activities present a risk to the communities mentioned and other downstream areas. Important to note, however, is that the results of testing will not only represent cumulative impacts from dam activity but will also include inputs from the nearby communities mentioned. So, the individual results in these areas cannot solely be attributed to dam activity. However, by utilizing the trends of sampling results from upstream areas it is possible to determine if dam activity is influencing downstream water quality. The results of Quarter 4 data suggest that that the Macal River within the downstream area is within range of a healthy riverine ecosystem. Despite periods of intense rain, most parameters were well below the upper limit.
In terms of the potential for dam breach, in January 2019, Gannett Fleming was commissioned by the Belize Electric Company Limited (BECOL) to prepare revised inundation mapping for the failure of Chalillo Dam and the subsequent cascading failures of Mollejon and Vaca dams. Fleming used state-of-the-art two-dimensional (2D) modelling and LiDAR terrain data. The scope of services included gathering and reviewing data, developing breach parameters, completing 2D hydraulic modelling, preparing inundation mapping and a dam break analysis report, and developing GIS deliverables and dam breach videos. The study reach extends downstream approximately 110 kilometers from Chalillo Dam to the town of Belmopan, including reaches of the Macal, Mopan, and Belize rivers.
Chalillo Dam has a drainage area of 883 square kilometers. The dam is a Roller Compacted Concrete (RCC) gravity structure with a design height of 47 meters. The dam consists of a 40-meter-wide central mass concrete ogee spillway, an 80-meter-wide RCC upper main spillway, and a 150-meter-wide auxiliary spillway. The combination of these three spillways provides the dam with significant flood control capability and necessary spill capacity.
In the event of a dam breach, the potentially impacted downstream area includes multiple road crossings and several developed communities including Black Rock, Negroman, Cristo Rey, San Ignacio, Bullet Tree Falls, Unitedville, Ontario Village, Teakettle, and Belmopan.
With a release of the large storage from the three dams (Chalillo, Mollejon, and Vaca dams), high flow velocities and flow momentum changes are anticipated as the breach wave travels downstream. Further downstream along the Macal River where the river reaches the town of San Ignacio and confluences with the Mopan River (before forming into the Belize River), the terrain flattens and has significant floodplain storage. Due to the flat nature of the floodplain terrain in this area, and the anticipated high level of flooding from the dam breach, multidirectional flow spreading is anticipated to occur in the floodplain near the river confluence. The multidirectional flow spreading at the confluence will have a significant impact on the attenuation of the flood wave. Breach flows are anticipated to flow upstream into the Mopan River as a backwater, create complex flow dynamics upstream of the confluence of Macal and Mopan rivers, and flow back downstream into the Belize River.
Several residential structures in and near the communities of Black Rock, Negroman, Cristo Rey, San Ignacio, Bullet Tree Falls, Santa Familia, and Mount Hope are estimated to be impacted by the breach outflows. Due to the significantly steep nature of the stream reach along with a characteristic narrow river valley for the portion of the Macal River between Chalillo Dam and the upstream end of the town of San Ignacio, outflows from a dam breach are estimated to have fast travel times in the range of 3 to 10 meters per second. The breach flood wave is anticipated to reach the town of San Ignacio within 4 hours from a breach, allowing limited time for warning and evacuation.
Downstream of San Ignacio, the terrain flattens and has a large floodplain that attenuates and reduces the speed of the flood wave. Water levels in the downstream rivers and water bodies are estimated to reach their peak and recede back to normal levels within 48 hours from the time of breach. The flood wave from the breach, once it reaches the confluence of Macal and Mopan rivers, is anticipated to cause backwater into the Mopan River to a location approximately 3 km upstream of Bullet Tree Falls. Flooding from this backwater is estimated to impact a number of structures in the town of Bullet Tree Falls. By the time the flood wave reaches the town of Ontario Village located approximately 80 km downstream of Chalillo Dam, breach outflows from a Sunny Day breach are estimated to be channelized and contained within the banks of the Belize River.
But what are BECOL’s measures in place in the event of a dam breach? The Dam Safety Emergency Preparedness Plan (EPP) is a key component of BECOL’s Dam Safety Management System (DSMS). BECOL has developed this EPP in accordance with the requirements of the Consolidated Environmental Compliance Plan (ECP). The EPP is designed to deal with any crisis (even though highly unlikely) experienced with the Chalillo, Mollejon, or Vaca Dam structures. The plan is developed in conjunction with relevant authoritative bodies responsible for activities during natural disasters in the area, in the interest of public safety.
BECOL installed and maintains an Early Warnings System (EWS) to assist in alerting residents in vulnerable areas in the event of an extreme flash flood scenario or in the unlikely event of a dam break. The EWS consists of a primary trigger at the Mollejon Control Room and seven base stations remotely connected via VHF Radios. All stations are strategically positioned in the most vulnerable and immediately affected population centers along the Macal, Mopan, and Belize Rivers. All EWS stations can be remotely triggered simultaneously from Mollejon Control Room and/or by onsite manual trigger switches at each station location.
BECOL inspects, maintains, and tests the EWS siren network on a monthly basis in order to ensure its functionality. EWS maintenance and testing are recorded, documented, and filed by BECOL for safekeeping. Copies of these records are also disseminated to the Department of Environment and National Emergency Management Organization in a timely manner.