Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hessd-11-9759-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
19 Aug 2014
Review status
This discussion paper is a preprint. A revision of the manuscript for further review has not been submitted.
Investigation of seasonal river–aquifer interactions in a tropical coastal area controlled by tidal sand ridges
H. Calderon1,2 and S. Uhlenbrook1,3 1UNESCO-IHE, Department of Water Science and Engineering, P.O. Box 3015, 2601 DA Delft, the Netherlands
2Nicaraguan Aquatic Resources Research Center at the National Autonomous University of Nicaragua (CIRA-UNAN), P.O. Box 4598, Managua, Nicaragua
3Delft University of Technology, Section of Water Resources, P.O. Box 5048, 2600 GA Delft, the Netherlands
Abstract. Water exchanges between streams and aquifers influence the quantity and quality of water in both domains. Seasonal river–aquifer interactions were investigated in a tropical coastal area where tidal sand ridges control river discharge to the sea. The study site is located in southwestern Nicaragua, dominated by humid tropical hydro-climatic conditions. The aquifer provides water to the rural town of Ostional. Connectivity between the river and the aquifer influences water quality and water availability for humans and for the downstream estuarine ecosystem. The effect of stream stage fluctuations on river–aquifer flows and pressure propagation in the adjacent aquifer was investigated analyzing high temporal resolution hydraulic head data and applying a numerical model (HYDRUS 2-D). Tidal sand ridges at the river outlet control the flow direction between the river and the aquifer. Surface water accumulation caused by these features induces aquifer recharge from the river. Simulations show groundwater recharge up to 0.2 m3 h−1 per unit length of river cross section. Rupture of the sand ridges due to overtopping river flows causes a sudden shift in the direction of flow between the river and the aquifer. Groundwater exfiltration reached 0.08 m3 h−1 immediately after the rupture of the sand ridges. Simulated bank storage flows are between 0.004–0.06 m3 h−1. These estimates are also supported by the narrow hysteresis loops between hydraulic heads and river stage. The aquifer behaves as confined, rapidly transmitting pressure changes caused by the river stage fluctuations. However, the pressure wave is attenuated with increasing distance from the river. Therefore, we concluded that a dynamic pressure wave is the mechanism responsible for the observed aquifer responses. Pressure variation observations and numerical groundwater modeling are useful to examine river–aquifer interactions and should be coupled in the future with chemical data to improve process understanding.

Citation: Calderon, H. and Uhlenbrook, S.: Investigation of seasonal river–aquifer interactions in a tropical coastal area controlled by tidal sand ridges, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hessd-11-9759-2014, in review, 2014.
H. Calderon and S. Uhlenbrook
Interactive discussionStatus: closed (peer review stopped)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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RC C6324: 'Review of the Manuscript „Investigation of seasonal river-aquifer interaction in a tropical coastal area controlled by tidal sand ridges“ by Calderon and Uhlenbrook', Anonymous Referee #1, 04 Feb 2015 Printer-friendly Version 
 
RC C6839: 'Review', Anonymous Referee #2, 20 Apr 2015 Printer-friendly Version 
H. Calderon and S. Uhlenbrook
H. Calderon and S. Uhlenbrook

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