Análisis hidrológico de la cuenca del río Sensunapán, como alternativa para el fortalecimiento de la gestión de riesgos y reducción de la vulnerabilidad, en el Departamento de Sonsonate, El Salvador

Abstract

This  study  was  conducted  in  Sensunapán  river  basin,  located  in  the  department  of  Sonsonate;  the  field  phase  was  implemented  in  November  2015 and was under study to analyze the hydrological behavior of the basin of river Sensunapán using tools Geographic Information System (GIS). The methodological  process  began  with  the  delimitation  of  river  watersheds  belonging to Sensunapán river from maps at 1: 25,000 National Registration Center    (CNR);    also    determined    the    corresponding    morphometric    characteristics. The biophysical and hydrological basin analysis was carried out  by  the  hydrological  classification  proposed  by  the  Soil  Conservation  Service. weighted runoff coefficient for the entire basin and the upper, back to  establish  biophysical  analysis  of  it  was  determined.  Time  concentration  was  determined  by  the  formula  Kirpich.  To  design  flows  of  the  basin,  the  average  intensity  of  the  rain  settled  through  the  historical  record  of  hydrometric stations in the municipalities of Chalchuapa, Juayúa, Apaneca, Izalco, Acajutla; which possess intensity data, duration and frequency; also they were taken as reference for the calculation of the flow, return periods of 02, 05, 10, 15 and 25, with a duration of 360 minutes for the entire basin and 150 minutes to the top of it. Hydraulic modeling was performed using software HEC - RAS 4.1.0, which allowed the calculation for different flow configurations in each of the cross sections along the two sections located in Vega del Rio and El Palmar communities; simulated levels of water depths and flow rates, among other variables values.

The  simulation  was  performed  considering  the  "tramoalto"  from  the  El  Palmar (Code: 1269.804) community to the "tramobajo" located in the Vega del Rio (Code .: 10.30199) community. The rate of flow in the cross section of the El Palmar community was critical sub character, with an increasing trend  in  the  number  of  Froude  with  values  of  0.32,  0.43,  0.48,  0.51  and  0.55, for return periods of 2, 5, 10, 15 and 25; thus indicating that the flow rates  are  lower,  but  his  elevation  hydraulic  is  greater;  ie  the  flow  travels  by  its  own  weight;  however,  the  rate  of  flow  in  the  corresponding  cross  section  to  the  Vega  del  Rio  community  was  critical,  a  Froude  number  of  1.13,  which  was  the  same  for  all  periods  above  mentioned  return,  in  this  way,  it  is  in  a  situation  where  conditions  are  generated  to  flow  turbulence  occurs and thus an increase in flow velocity resulting in increased channel erosion  and  undermining  of  the  inhabited  areas.  From  the  hydrological  point of view, the upper part of the basin has good hydrological condition, consisting of areas of coffee crops and forests, and soil type whose physical properties  with  moderate  infiltration  rates  and  water  transmission  define  a  condition moderate runoff potential; however, the design flows under these biophysical  characteristics  indicate  a  threat,  due  to  the  characteristics  of  human settlements in the lower part of the basin. The characteristics of the flow  channel  of  Sensunapán  river  up  to  the  Vega  del  Rio  community,  has  a high degree of erosive capacity, meaning susceptibility to undercuts due to  the  speed  that  the  flow  has  on  that  site,  represented  this  in  an  increase  community vulnerability.