Environmental flow calculation for the maintenance of the water reserve of the Piaxtla River, Sinaloa, Mexico | Cálculo del flujo ambiental como sustento para la reserva de agua al ambiente del río Piaxtla, Sinaloa, México

Inglés. The calculation of river flows necessary to maintain the environmental services of the diverse river basins in Mexico has been an element to be considered in complying with the Mexican Norm and in allowing an adequate administration of water resources. Several methods have been proposed for this calculation, among which a very simple one is a hydrological method that requires a data base on runoff to determine the volume of water that ecosystem functions need. Hydrological methodology proposed by the NMX cited above, provides guidelines for establishing a regime as a percentage of average annual runoff and it is assumed maintain biological attributes at certain levels of conservation. It also analyzes the regime of seasonal normal flow for wet hydrological conditions, socks, dry and very dry, and the system of avenues (considered as the sudden increase in the volume and speed of the current in a river due to runoff resulting from rain cyclical or extraordinary, it is also known as flooding), considering at least three categories of avenues (intra-annual, annual and interannual low magnitude of average size) with corresponding attributes of magnitude, duration, frequency, time of occurrence and rate exchange. For greater certainty calculation it will always be necessary to have records in the three levels of a basin. This level of analysis is to determine the final volume of ecological flow, considering the benchmark to achieve the previously defined environmental objective. For ecological calculation referred by the NMX, some fundamental aspects were considered, such as: ecology importance (which ranks among very high, high, medium and low based on the concepts of the rule itself ); use pressures (determined as the ratio percentage of the volume allocated over the concession between the annual average availability basin or aquifer, determined as high ≥ 80%, ≥ 40% high, medium and low ≥ 11% ≤ 10%) ; the environmental objective (ecological status to be achieved within the watershed to maintain the integrity of existing ecosystems or when they believe that they are degraded, contributing to the recovery or rehabilitation); and annual percentage rate recommended for environmental protection. Based on this, the purpose of this study was to quantify the river flow of the Piaxtla river, in the state of Sinaloa. The river runoff data bases for 36 and nine years were compared, showed differences mainly between the frequency of maximum runoff and its origin, and indicated that it is advisable to use a data base of more than 20 years. However, results were similar in the final calculation of the environmental or ecological river flows; that is to say, total runoff volume was 62.1% considering 36 years and 57.7% for nine years of information. We conclude that the ecological importance of Piaxtla river was very high and the use of water pressure was low (considering that database runoff only included until 1999 and did not take into account population growth and activities). To determine the final volume reserved for the environment or ecological flow, could be estimated not only with a database of 36 years, but for nine years also confirming that those rivers that have databases of 10 years can the methodology used hydrological indicated by the NMX said. Particularly in this study it was determined that for parameters more detailed as the volume of the base rate of the annual volume, according to the frequency of occurrence, both very dry years, dry, average and wet, and influence of meteorological events that determine periods separate return, it is advisable to use minimum data bases as brand NMX 20 years.

Español; castellano. El cálculo del caudal fluvial necesario para mantener los servicios ambientales de los diferentes tipos de cuenca en los ríos de México, ha sido un elemento a cumplir en la Norma Mexicana, lo que permite una adecuada administración del recurso hídrico. Para dicho cálculo se han propuesto diferentes metodologías, una de las cuales por su sencillez es la hidrológica, requiriendo para ello una base de datos de escurrimientos que permitan determinar el volumen de agua necesario para las funciones de los ecosistemas. Con base en lo anterior, el objetivo de este estudio fue estimar dicho caudal en el río Piaxtla, Sinaloa. Para ello se compararon bases de datos de escurrimientos de 36 y nueve años que mostraron diferencias fundamentalmente entre la frecuencia de las máximas avenidas y sus orígenes, lo que recomienda contar con base de datos mayores a veinte años; sin embargo, en el cálculo final del caudal ambiental los resultados fueron semejantes, es decir, reservar del volumen total del escurrimiento el 62.1% considerando un lapso de 36 años de estudio y 57.7% tomando en cuenta nueve años de información.