Bathymetric Study of Loiza Reservoir, Puerto Rico

Client: Puerto Rico Aqueduct and Sewer Authorithy (PRASA)

Contract Period: 2019 (Project Duration: 4 months)

The Puerto Rico Aqueduct and Sewer Authority (PRASA) owns and operates the Loíza dam and reservoir. This system is one of the most important sources of water for the Puerto Rico metropolitan area, supplying raw water to the Sergio Cuevas filtration plant. Sedimentation has been the principal threat to this system, and now almost 46% of storage capacity has been lost due to sediment accumulation. This situation has led to a continuous reduction in firm yield. In 1997 the reservoir was dredged recovering 6 Mm3 part of the lost storage volume, returning capacity to about 20.6 Mm3.

This study was performed to determine the current storage capacity of Lago Loíza. This new sedimentation survey was used to establish the rate of sedimentation and the volume lost since the last sedimentation survey performed in 2009. In addition, the study defined the amount of sediment deposited in the reservoir during the passage of hurricane María on September, 2017.

A 50-meter survey interval was used along the reservoir, the same interval used in the previous sedimentation survey. A total of 209 sections were surveyed. Survey work extended upstream from the dam up to the confluence of Río Grande de Loíza and Río Gurabo.

The study concluded that: 1. The inter-survey rate of volume loss appears to be reducing over the past 15 years. This behavior is also noticeable during the period of 1971 to 1994 when the reservoir had a similar storage volume. 2. The storage volume gained by dredging (1997) has been essentially lost due to new sediment accumulation.