Progress 01/01/00 to 12/30/05
Outputs
Tropical watersheds in Puerto Rico are subjected to intense rainfall precipitation during the hurricane season from June to November each year. The energy associated with these storms generates important amounts of soil detachment and transport to streams and eventually to reservoirs and coastal valleys around the island. This project has monitored over 40 extreme runoff events in five selected sub-watersheds within the larger Rio Grande de Arecibo in north central Puerto Rico. A continuous simulation model of the erosion-sediment transport processes, using HSPF, was calibrated and validated with historical climatological data from 1995 to 2001. Consecutive bathymetry surveys of the Dos Bocas and Caonillas reservoirs provided mass loads of accumulated sediment that were used to assess model accuracy by comparing model prediction of sediment export from the watershed and mass accumulation at the reservoir bottom. The calculated sediment yield (from bathymetry studies)
at the lake was 3.34 t ac-1 yr-1, the model was able to account for 1.60 t ac-1 yr-1, or about 48% of the sediments incoming into the Dos Bocas reservoir. The remaining 52% (1.74 t ac-1 yr-1) was not accounted for but this finding it sheds light on the shortcomings embedded in typical erosion-transport process models that cannot account for stream bank and stream bed erosion. Partial finding of this study indicates that agricultural lands produced the highest total sediment losses, corresponding to 54% of total soil losses. Calculated sediment export coefficients for agricultural lands for the research period ranged from 0.12 to 0.55 t ac-1 yr-1. For barren land, sediment export coefficient ranged from 0.33 to 14 t ac-1 yr-1; for forest land, from 0.003 to 0.019 t ac-1 yr-1; for rangeland, from 0.009 to 0.022 t ac-1 yr-1, and for pasture was from 0.015 to 0.063 t ac-1 yr-1. For the simulation period between 1 October 1995 and 29 February 2000 in the Caonillas reservoir the model
accounted for 10.7 E06 tons of sediments, which represents a 9.5% difference of the sediments accumulated in the lake from that reported by a USGS study. For the simulation period for Dos Bocas reservoir between 1 October 1995 and 30 September 1999, the model accounted for 17.6 E06 tons of sediments, which represents a 20.1% difference from that of the USGS measured value. The sediment export coefficient values for agricultural lands were within the tolerance limits suggested for similar soils in Puerto Rico. The rate of soil erosion from barren lands (sand mines and domestic landfill) was 210 times greater than that from herbaceous areas.
Impacts
Tropical watersheds can be steep and have shallow soil depths, features that make them respond very quickly to typical intense precipitation events. As a result, soil detachment and transport is a severe problem that endangers life and infrastructure projects. This study area provides potable water to nearly 50% of the island's population concentrated in the metropolitan area of San Juan, Puerto Rico, through a recently installed aqueduct with maximum yield capacity of 100 million gallons per day (MGD). The sustainability of this infrastructure project relies entirely on the capacity of the watershed, herein studied to continue to supply potable water, but there are many challenges that need to be overcome, including and most importantly the design and implementation of management practices in tropical watersheds to reduce the risk of soil erosion and siltation of reservoirs. This project provided quantifiable and specific response of the soils within the watershed to
water erosion and land use practices. These results can provide a powerful tool to watershed managers to designate locations to foster urban/industrial and agricultural development and places where preservation is recommended to reduce the risk of soil erosion and sedimentation of this important water producing system.
Publications
- Perez-Alegria, L.R., D. Sotomayor, G. Martinez and G. Suarez. 2005. Hydrologic analysis for nutrient load determinations. J. Am. Water Resources Assoc. June 2005. Submitted.
- Suarez-Narvaes, G.A. 2005. Sediment export coefficients for Rio Grande de Arecibo watershed. M.Sc. Thesis. Civil Engineering Dept. University of Puerto Rico. Mayaguez, Puerto Rico.
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Progress 01/01/04 to 12/31/04
Outputs
Tropical watersheds in Puerto Rico are subject to intense rainfall precipitation during the hurricane season from June to November each year. The energy associated with these storms generates important amounts of soil detachment and transport to streams and eventually to reservoirs and coastal valleys around the island. This project has monitored over 40 extreme runoff events in five selected sub-watersheds within the larger Rio Grande de Arecibo in north central Puerto Rico. A continuous simulation model of the erosion-sediment transport processes was calibrated and validated by using historical data from 1995 to 2001. Using bathymetry data from a downstream reservoir, the calculated sediment yield at the lake was 3.34 ton ac-1 yr-1, the model was able to account for 1.60 ton ac-1 yr-1, or about 48% of the sediments coming on the reservoir. The remaining 52% (1.74 ton ac-1 yr-1) was not accounted for, but it sheds light into the shortcomings embedded in typical
erosion-transport process models that cannot account for stream bank and stream bed erosion. Partial findings of this study indicate that agricultural lands produced the highest total sediment losses, corresponding to 54% of total soil losses. The rate of soil erosion from barren lands (sand mines and domestic landfill) was 210 times greater than that from herbaceous areas. Soil loss per land use type in the study area was 0.03 for forest lands, 0.31 for herbaceous lands, 4.49 for agricultural lands, 1.59 for urban areas, 70.14 for barren areas and 0.31 ton ac-1 yr-1 for pasture lands.
Impacts
Tropical watersheds can be steep and have shallow soil depths, features that make them respond very quickly to typical intense precipitation events. As a result, soil detachment and transport is a severe problem that endangers life and infrastructure projects. The area studied provides potable water to nearly 50% of the island population concentrated in the metropolitan area of San Juan, Puerto Rico, through a recently installed aqueduct with maximum yield capacity of 100 million gallons per day (MGD). The sustainability of this infrastructure project relies entirely on the capacity of the watershed study to continue to supply potable water. There are many challenges that need to be overcome, including, and most importantly, the design and implementation of management practices in tropical watersheds to reduce the risk of soil erosion and siltation of reservoirs. This project will provide quantifiable and specific recommendations for watershed management to foster
urban/industrial and agricultural development and recommendations for places where preservation is recommended to reduce the risk of soil erosion and sedimentation of this important water producing system.
Publications
- Diaz-Ramirez, J.N. 2004. Modeling Sediment Export Potential of the Rio Caonillas Watershed. M.Sc. Thesis. University of Puerto Rico. Mayaguez, Puerto Rico.
- Perez-Alegria, L.R., G. Suarez, D. Sotomayor and G. Martinez. 2004. Hydrologic analysis of nutrient and sediment loading determinations in tropical watersheds. 2004 Western Pacific Geophysics Meeting. 16-20 August 2004. Honolulu, Hawaii.
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Progress 01/01/03 to 12/31/03
Outputs
Objective 1 has been reached for this project: The databases for the entire Rio Grande de Arecibo (RGA) have been completed, including satellite imagery and aerial photography for detail land use mapping of the area. Work on Objective 2 (Develop a watershed management plant for soil erosion prevention and sedimentation) was initiated in 2003. Continuous runoff and sediment export predictions started at the higher elevations. Work will continue towards the outlet of the watershed at the dam site of Lake Dos Bocas. Work towards objective 3 (To train students in the use of advance technology for the appropriate management of watershed resources) has continued and will continue throughout the duration of the project. Specifically the following tasks were performed: Objective 1: 1. The GIS of the RGA w/s is 95 percent completed. Land use coverage of the w/s was obtained from several sources, including satellite imagery, aerial photography and interviews and site visits
with agricultural extension agents of neighboring towns. 2. All coverages required for the simulation were prepared and assembled into the HSPF model. 3. Water and sediment samples for individual storm events are being collected at four monitoring stations installed at four subwatersheds of the RGA catchment area. Objective 2: 1. Four water and sediment sampling stations were set up at four sub-watersheds within the RGA catchment area (Rio Caonillas, Rio Saliente, Rio Limon and Rio Grande de Arecibo). These sampling stations are located next to USGS gauging stations. 2. Time series analyses of flow and suspended sediments are being conducted and compared with continuous simulation runs performed for the period 1998-2003. Simulations are performed using Hydrologic Simulation Program-Fortan (HSPF) in the BASINS interface. 3. An additional effort is underway to assemble the model in SWAT to compare performance of the two models in tropical watersheds. Objective 3: 1. In addition to two
continuing graduate students who work in the project, two new graduate students were incorporated into the project. Edwin Martinez and Dewell Paez began graduate school in August 2003. Graduate students = 4
Impacts
This project will positively impact water resources in the northern corridor of Puerto Rico from Arecibo to the metropolitan San Juan area. The RGA watershed supplies potable water to over 1.5 million people in the service area. Findings from this project will provide much required physical information of land use management and planning for the continuous production of water and the reduction of soil erosion and siltation of lakes and reservoirs.
Publications
- Perez-Alegria, L.R. and J. Diaz. 2003. Modeling Sediment transport with HSPF. 2nd Conference on TMDL. Albuquerque, NM. December 8-12, 2003.
- Diaz, J. and L.R. Perez-Alegria. 2003. Sediment modeling and transport in a tropical watershed. 39th International Meeting of the American Society of Agricultural Engineers. Paper number: 03. July 21-27, 2003. Las Vegas, NV.
- Perez Alegria, L.R., and J. Diaz. 2003. Sediment modeling and transport in a tropical watershed. Annual meeting of the Caribbean Food Crops Society. July 16-19, 2003. St. Georges, Grenada.
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Progress 01/01/02 to 12/31/02
Outputs
Work continues on objectives one and three of the project. Objective 1: to compile the database necessary to predict soil erosion in the Rio Grande de Arecibo (RGA) watershed (w/s). Objective 3: to train students in the use of advanced technology for the appropriate management of w/s resources. Specifically the following tasks were performed: Objective 1: 1) The GIS of the RGA w/s is 80 percent completed. The databases obtained from the PR Planning Board and the US Geological Survey were assembled to conform to the RGA watershed. 2) Sediment and water quality sampling stations in the RGA are shown in Figure 2. These sampling stations, managed by the Environmental Quality Board (EQB) of Puerto Rico, were selected to develop the hydrology of each sub-basin. 3) Digital Elevation Models (DEM) for the same quad sheets were obtained from the USGS web site and transformed to ArcView GIS. 4) The USDA-NRCS and other local agencies run an interagency group that is currently
working with the RGA w/s. 5) The PI participated in the 32nd Conference of the International Erosion Control Association and took two professional development courses at the meeting. 6) Images from Landsat 7 are being processed, for land use classification. A recent Ikonos image taken in 2002 is also used to develop up to date land use maps. 7) Georeferencing of land uses within the watershed is underway. 8) The watershed modeling system (WMS v6) is being used to build the modeling system for sediments and flow in the two build sub-watersheds of Rio Caonillas and Rio Saliente. 9) The Rio Limon watershed (22,428 Ac) was included in the analysis. Land use maps and hydrologic analysis are underway. A monitoring and sampling station will be installed next. Objective 3: Two graduate students are currently working on this project, Jairo Diaz and Gustavo A. Suarez. A third graduate student started working on this project but stopped shortly after the first year of work. 1) Graduate student
Jairo Diaz attended a one-week training workshop on BASINS 3.0 at Utah State University, Logan, Utah during the period of May 5-11, 2002. 2) Graduate student Jairo Diaz spent a month (June 3 to July 3, 2002) at Cornell University with the modeling group of Dr. Tammo Steenhuis, getting acquainted with the Soil Moisture Routine model (SMR) developed by this group. 3) Undergraduate student Alex Rivera, a former student from the College of Agricultural Sciences (CAS), spent ten weeks at the Stennis Space Center, Stennis Mississippi, getting exposed to and receiving training on the use of remote sensing tools for analysis and interpretation of Landsat images of Puerto Rico.
Impacts
This project has the potential of positively impacting water resources in the RGA and the northern corridor from Arecibo to San Juan. The project will provide guidelines to recover degraded lands by utilizing vegetative covers in specific areas to: 1) maintain or augment vegetative land cover and forest resources within the RGA watershed; 2) augment water resources within the RGA and the northern corridor from Arecibo to San Juan, and 3) reduce soil loss and siltation of the Dos Bocas reservoir.
Publications
- Perez-Alegria, L.R.; Sotomayor, D.; Rivera, L.; and Martinez, G., 2002. Development of TMDL for a Tropical Watershed in Puerto Rico. Poster presented at the Watershed Management to Meet Emerging TMDL Environmental Regulations conference and exhibition on March 11-13, 2002, Fort Worth, Texas.
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Progress 01/01/01 to 12/31/01
Outputs
Work continues on objectives one and three of the project. Objective 1: to compile the database necessary to predict soil erosion in the Rio Grande de Arecibo (RGA) watershed (w/s). Objective 3: to train students in the use of advance technology for the appropriate management of w/s resources. Specifically the following tasks were performed: Objective 1: A 1999 SPOT satellite image of the w/s was obtained from the Puerto Rico Department of Natural Resources and Environment (DNRE). This image will help to develop current land use in the w/s. The entire w/s has been visited to correctly classify land use. This procedure is known as ground truthing. The software Watershed Modeling Systems (WMS) has been used to develop the model for the RGA w/s. This model is being implemented in three sub-basins within the w/s to study soil erosion and impact of land use on sediment export. Objective 3: Two graduate and three undergraduate students participated in this project. They
will continue to participate. Part of the funding to support students comes from other projects in the same watershed. A graduate student attended an intensive course on image classification in Washington, D.C., in October 2001. A second graduate student will be attending a watershed modeling course in May 2002. Two undergraduates will participate in related work at NASA and the University of Illinois summer 2002. GSY=2
Impacts
This project will provide guidelines to recover degraded land by utilizing vegetative covers in specific areas to: 1) maintain or augment vegetative land cover and forest resources within the RGA watershed; 2) augment water resources within the RGA; and 3) reduce soil loss and improve water quality in the RGA river.
Publications
- Perez-Alegria, L., Sotomayor, D., Martinez, G., and Rivera A., 2002. Developing TMDL's in a Tropical Watershed. Watershed Management to Meet Emerging TMDL Environmental Regulations Conference. March 11-13, 2002. Fort Worth, TX.
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Progress 01/01/00 to 12/31/00
Outputs
A geographic information system for the Rio Grande de Arecibo (RGA) watershed is 50 percent complete. The soil database has been digitized. The relational database and the polygon attribute table for the soil coverage is 50 percent complete. A digital elevation model for the watershed has been ordered. Satellite imagery for years 1985 and 2000 have been procured to begin the classification process and study of land use change trends.
Impacts
This project will positively contribute to the sustainability of the watershed as an important water resource watershed. The work addressed by the project relates to the best utilization of sustainable watershed practices for maintaining the soil in place and reducing soil erosion, thus reducing siltation of water supply reservoirs in the RGA watershed.
Publications
- No publications reported this period
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