When using numerical models for hydraulic simulations of rivers, calibration is key to be able to reflect accurately the interaction of water flow in the channel and to make it resemble what is observed. In this study, a calibrated two-dimensional hydraulic model was created for two control paths located in the Ahogados and Tempisquito rivers. Paths were analyzed morphologically from a grain-size analysis and the different roughness coefficients were calculated through a numerical model using the empirical equations known as “Strickler-type” as a first approximation and later adjustment by a factor obtained from comparing the observed and simulated data. It was identified that both paths are mountain rivers with beds of coarse material, mostly boulders (cobble gravel) and pebble gravel. Calibrated roughness coefficients were determined with an error percentage between the area of the pattern formed by the simulated and observed of less than 10%, and new empirical equations adjusted to the characteristics of the riverbeds were formulated.

The study of environmental flow has garnered significant scientific interest due to the considerable degradation caused by human activities on aquatic ecosystem dynamics. Environmental flow is defined as the quantity, timing, and quality of water flow required to sustain freshwater and estuarine ecosystems while meeting human demands. Research in riverine ecosystems can generate the critical scientific knowledge needed to determine an adequate environmental flow that balances the requirements of both aquatic organisms and human populations. This study is part of a series of investigations aimed at field-testing different methodologies to determine appropriate environmental flow levels for rivers with specific characteristics. In particular, we adapted and validated a holistic methodology for calculating the environmental flow regime in the Tempisque River basin in Costa Rica. This research involved analyzing hydrological parameters, hydraulic conditions, the presence of flow bioindicators, and various anthropogenic uses of the river (such as human consumption, productive, recreational, and cultural activities) to estimate environmental flow requirements throughout the year. The findings indicate that the lower and upper limits of the environmental flow for the studied section of the Tempisque River correspond to the monthly excesses of 95.00% and 64.00%, respectively. These results provide a reliable annual flow regime that can inform decision-making by authorities in water resource management, particularly in regions where there is a high demand for water across different human activities.

The consequences of climate change have challenged researchers to generate models and projections to understand climate behavior under different scenarios. In Costa Rica, as in other countries, climate-change (CC) models and projections are essential to make decisions about the management of natural resources, mainly water. To understand climate change’s impact on hydraulic parameters such as velocity, depth, and river surface area, we studied the Pejibaye river basin, located in Jiménez in Cartago, Costa Rica. This watershed is characterized by having more than 90% of its surface area covered by forest. We used the precipitation and temperature data from meteorological stations (2000 to 2009) and climate-change scenarios (2000–2099) to predict the response of the basin in different periods. First, we calibrated (NSE = 0.77) and validated (NSE = 0.81) the HBV hydrological model using ten years of daily data from 2000 to 2009. The climate-change data (2000–2099) were incorporated into the calibrated HBV model. This allowed us to determine the impact of CC on the basin water regime for the periods 2040–2059 (CCS1) and 2080–2099 (CCS2). The IBER mathematical model was used to determine the changes in the hydraulic variables of the river flow. For the CCS1, we determined a 10.9% decrease in mean velocity and a 0.1-meter decrease in depth, while for CCS2, the effect will be an 11.3% reduction in mean velocity and a 0.14-meter decrease in depth. The largest decreases in river surface area per kilometer will occur in May (1710 m²) for CCS1 and April (2250 m²) for CCS2.

The environmental flow, in Costa Rica, is calculated as 10% of the average flow of the river. This percentage has lacked scientific basis in relation to the river conditions suitable for preserving the ecosystems present in the rivers. The water concessions for the different uses have caused an environmental impact that is reflected in the conditions of availability of the water resource in some vulnerable points of the country, as well as in the physicochemical and ecological conditions of the channels. The proposed project responds to the research route that seeks the selection and field validation of different methodologies to obtain the required environmental flow in a surface water source. In this particular case, the project is focused on the adaptation and validation of a hydrobiological methodology for calculating the environmental flow regime in Pejibaye river basin, Jimenez de Cartago. Historical hydrological data variables were used to analyze the current and projected future condition, the species of macroinvertebrates and fish that allowed evaluating the quality of the associated ecosystems were selected, finally, the hydraulic parameters of habitat preference were established to define the current environmental flow regime, whose results reveal a seasonality behavior, which is accentuated in the future projection. The insect genus Anacroneuria and the fish species G. nudus were determined to be the best for determining environmental flows.

La proximidad de las áreas urbanas y de agricultura extensiva a los ríos de la vertientes del Atlántico en Costa Rica, contrasta con su morfología inestable. Adicionalmente, los cambios en el régimen de lluvias han incrementado la frecuencia de desastres naturales afectando regularmente a las población cercanas y la economía del país. Se necesitan estudios detallados que demuestren el impacto de los ríos en áreas urbanas y alta actividad agrícola para establecer medidas adecuadas de mitigación y control de inundaciones. El presente estudio muestra un caso del impacto de un evento de inundación de 25 años en la planicie de inundación del Río Matina en Costa Rica, mediante una modelación hidaúlica bidimensional con el objetivo de contribuir a un adecuado manejo del uso del suelo y establecer medidas de protección en la zona de estudio. Un modelo de elevación digital, de la topografía del área de estudio, obtenido con un dispositivo LIDAR, y la estimación del caudal pico instantáneo se obtuvo con la distribución estadística de Weibull para un periodo de retorno de 25 años, permitiendo brindar información satisfactoria para para el análisis de inundaciones de combinaciones complejas para la gestión del drenaje superficial. Se analizaron dos escenarios para el manejo de inundaciones: 1) aumento de la altura del dique y 2) apertura anticipada de una desembocadura adicional en la desembocadura del río durante los eventos de inundación. El estudio demostró que ninguna de las opciones era técnicamente factible y que los tomadores de decisiones deberían explorar otras alternativas de mitigación de inundaciones.

En Costa Rica el caudal ambiental se calcula como un 10% del aforo caudal medio del río. Este porcentaje ha carecido de fundamento científico en relación con las condiciones fluviales aptas para preservar los ecosistemas presentes en los cauces. Las concesiones de agua para los diferentes usos han provocado un impacto en disponibilidad de agua para algunos lugares y épocas del año y en la calidad del recurso transformando las condiciones fisicoquímicas y ecológicas de los cauces. Del sistema fluvial del río Birrís, se concesiona un 20% para uso consuntivo como producción agrícola, humano y riego, y el restante se utiliza para la generación hidroeléctrica. Debido a la baja calidad de sus aguas a la fecha no existen especies indicadoras lo que imposibilita el uso de enfoques que tomen en cuenta los ecosistemas para generar curvas de preferencia. El presente trabajo utilizó un enfoque hidrológico para determinar el caudal ambiental del río Birrís usando la metodología de curva de duración de caudales. Se basó en el análisis de series de datos de clima obtenidas por 10 años y series de caudales diarios de un periodo de tres años. Se realizaron tres aforos de biota y flujo en tres puntos distribuidos a lo largo del cauce principal distribuidos en un periodo de un año. Finalmente, se determinó el caudal ambiental para un régimen de flujo basado en valores medios mensuales.