Numerical Simulation of Water Renewal Timescales in the Mahakam Delta, Indonesia
by
Chien Pham Van 1,*, Benjamin De Brye 2, Anouk De Brauwere 3, A.J.F. (Ton) Hoitink 4, Sandra Soares-Frazao 5 and 
Eric Deleersnijder 6
Chien Pham Van 1,*, Benjamin De Brye 2, Anouk De Brauwere 3, A.J.F. (Ton) Hoitink 4, Sandra Soares-Frazao 5 and Eric Deleersnijder 6
1
Department of River Engineering and Disaster Management, Thuyloi University, 175 Tay Son, Dong Da, Hanoi 100000, Vietnam
2
Free Field Technologies (FFT), 1435 Mont-Saint-Guibert, Belgium
3
Karel de Grote Hogeschool, Chemie en Biomedische Laboratoriumtechnologie, Salesianenlaan 90, 2660 Antwerp, Belgium
4
Hydrology and Quantitative Water Management Group, Department of Environmental Sciences, Wageningen University, 6708PB Wageningen, The Netherlands
5
Institute of Mechanics, Materials and Civil Engineering (IMMC), Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
6
Institute of Mechanics, Materials and Civil Engineering (IMMC) & Earth and Life Institute (ELI), Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
*
Author to whom correspondence should be addressed.
Water 2020, 12(4), 1017; https://doi.org/10.3390/w12041017
Received: 9 March 2020 / Revised: 30 March 2020 / Accepted: 30 March 2020 / Published: 2 April 2020
(This article belongs to the Special Issue Tracer and Timescale Methods for Passive and Reactive Transport in Fluid Flows)
Water renewal timescales, namely age, residence time, and exposure time, which are defined in accordance with the Constituent-oriented Age and Residence time Theory (CART), are computed by means of the unstructured-mesh, finite element model Second-generation Louvain-la-Neuve Ice-ocean Model (SLIM) in the Mahakam Delta (Borneo Island, Indonesia). Two renewing water types, i.e., water from the upstream boundary of the delta and water from both the upstream and the downstream boundaries, are considered, and their age is calculated as the time elapsed since entering the delta. The residence time of the water originally in the domain (i.e., the time needed to hit an open boundary for the first time) and the exposure time (i.e., the total time spent in the domain of interest) are then computed. Simulations are performed for both low and high flow conditions, revealing that (i) age, residence time, and exposure time are clearly related to the river volumetric flow rate, and (ii) those timescales are of the order of one spring-neap tidal cycle. In the main deltaic channels, the variation of the diagnostic timescales caused by the tide is about 35% of their averaged value. The age of renewing water from the upstream boundary of the delta monotonically increases from the river mouth to the delta front, while the age of renewing water from both the upstream and the downstream boundaries monotonically increases from the river mouth and the delta front to the middle delta. Variations of the residence and the exposure times coincide with the changes of the flow velocity, and these timescales are more sensitive to the change of flow dynamics than the age. The return coefficient, which measures the propensity of water to re-enter the domain of interest after leaving it for the first time, is of about 0.3 in the middle region of the delta.
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Keywords:
Mahakam Delta; age; residence time; exposure time; return coefficient; CART
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MDPI and ACS Style
Pham Van, C.; De Brye, B.; De Brauwere, A.; Hoitink, A.T.; Soares-Frazao, S.; Deleersnijder, E. Numerical Simulation of Water Renewal Timescales in the Mahakam Delta, Indonesia. Water 2020, 12, 1017.
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