Modelling Approaches to Understand Salinity Variations in a Highly Dynamic Tidal River the case of the Shatt al-Arab River Ali Dinar Abdullah MODELLING APPROACHES TO UNDERSTAND SALINITY VARIATIONS IN A HIGHLY DYNAMIC TIDAL RIVER the case of the Shatt al-Arab River MODELLING APPROACHES TO UNDERSTAND SALINITY VARIATIONS IN A HIGHLY DYNAMIC TIDAL RIVER the case of the Shatt al-Arab River DISSERTATION Submitted in fulfilment of the requirements of the Board for Doctorates of Delft University of Technology and of the Academic Board of the UNESCO-IHE Institute for Water Education for the Degree of DOCTOR to be defended in public on Monday, 21 November 2016, 15:00 hours in Delft, the Netherlands by Ali Dinar ABDULLAH Master of Science in Water Resources Management, UNESCO-IHE born in Missan, Iraq This dissertation has been approved by the supervisors Prof.dr.ir. P. van der Zaag UNESCO-IHE / TU Delft Dr.ir. I. Popescu UNESCO-IHE / TU Delft Dr.ir. U.F.A. Karim University of Twente Composition of the doctoral committee: Chairman Rector Magnificus TU Delft Vice-Chairman Rector UNESCO-IHE Prof.dr. ir. P. van der Zaag UNESCO-IHE/TU Delft, promotor Dr.ir. I. Popescu UNESCO-IHE/TU Delft, copromotor Dr.ir. U.F.A. Karim University of Twente, copromotor Independent members: Prof.dr. N. Al-Ansari Lulea University, Sweden Prof.dr. F. Martins University of Algarve, Portugal Prof.dr.ir. H.H.G. Savenije TU Delft Prof.ir. E. van Beek University of Twente Prof.dr. W.G.M. Bastiaanssen TU Delft, reserve member CRC Press/Balkema is an imprint of the Taylor & Francis Group, an informa business © 2016, Ali Dinar Abdullah Although all care is taken to ensure integrity and the quality of this publication and the information herein, no responsibility is assumed by the publishers, the author nor UNESCO-IHE for any damage to the property or persons as a result of operation or use of this publication and/or the information contained herein. A pdf version of this work will be made available as Open Access via http://repository.tudelft.nl/ihe This version is licensed under the Creative Commons Attribution-Non Commercial 4.0 International License, http://creativecommons.org/licenses/by-nc/4.0/ Published by: CRC Press/Balkema PO Box 11320, 2301 EH Leiden, the Netherlands [email protected] www.crcpress.com – www.taylorandfrancis.com ISBN 978-1-138-62625-6 (Taylor & Francis Group) SUMMARY Densely populated delta regions in hot climates are vulnerable to acute water availability and water quality problems, problems that are often interrelated. One of the biggest threats to water quality in such areas is salinity. Declining freshwater inflows of deteriorating quality are among the major issues faced by many such deltaic rivers and their dependent human- and ecosystems, notably in their most downstream areas, which are close to the major salinity sources from seawater, intensive farming, industrial and population hubs. The more surface water is diverted to fulfil demands for freshwater, especially during long drought periods, and the lower the quality of water that is returned to the main stream, the more inland the tidal excursion and seawater intrusion will penetrate. Water insecurity and ecosystem decline result with major socio-economic implications. Some of the immediate causes and effects of salinity may be evident by the naked eye but the full picture is less obvious in terms of longer-term consequences and strategies for remediation. The process of salinization in rivers is dynamic and complex. It is multi-variate and can be highly variable, even random given the many factors and uncertainties associated with it. Determining these factors is data-intensive and case-specific and should therefore be tailor-made to past and current prevailing field conditions of salinity and a delta’s hydrology and water use. Salinity studies in complex deltaic systems require therefore reliable historic data based on systematic field monitoring, preferably covering all possible sources of water salinity. This is essential for developing verifiable analytical and numerical models that are based on field- calibrated parameters that are system-specific. With appropriate monitoring and modelling of sufficient refinement rational diagnostic and policy decisions can be made for mitigating both water scarcity and salinity, which ultimately should lead to sustainable water development. vi The present research is the first systematic monitoring and modelling study on water availability, water quality and seawater intrusion of the Shat al-Arab River (SAR). The SAR runs partially along the disputed international Iraq-Iran border, which has been a source of conflict in the past. It is an oil-rich area that has been continuously populated and cultivated since the beginning of civilization, characterised by the world's largest marshes and date-palms' forests. The Tigris and Euphrates rivers on the Iraqi side, and the Karkheh and Karun rivers originating in Iran, constitute the main water sources for the river and have allowed the region’s rich ecological, socio-economic and cultural heritage. The river mouth on the Gulf is also an important shipping route on which the densely-populated Iraqi city of Basra with its huge ports and oil export terminals are situated. The present research is timely and relevant for the issues of origin, regulation, and management of salinity in the SAR have become highly politicized and are hotly-debated at provincial and national levels. Current scientific knowledge on the SAR salinity problem is deficient, partially due to the complex, dynamic, and spatiotemporal interaction between salinity sources with water withdrawals and return flows by users of the different water sectors. The main objective of this research is to provide a sufficiently refined and consistent set of observations, both in space and time, with which to examine the salinity dynamics of the deltaic SAR system. The methodology used in this study was based on employing and combining various modelling approaches, underpinned by field data collected through a network of water quality sensors (divers). A systematic, comprehensive, and accurate monitoring program of salinity and water level over the entire length of the estuary and river (200 km) was developed for the first time under extremely harsh climatic and strict security conditions, yielding a unique dataset. Ten diver stations were installed at carefully selected locations, well maintained and regularly calibrated. Hourly observations of water level, temperature, and salinity variations during the full year 2014 were made. This part of the study determined the statistical, temporal and spatial distribution of salinity and its major causes, combining the 2014 data set with historical datasets gathered from local water authorities. A quantitative analysis of the 2014 data set, combined with historical data, resulted in a broad description of the SAR’s current state of hydrology and geography and the vii severe decline in water quantity and escalating levels of salinity over time (Chapter 3). The analyses covered the SAR as well as all contributing rivers (Euphrates, Tigris, Karkheh and Karun) with their connecting marshlands, which is essential to present a holistic picture. The analyses were based on the most recent data, though limited, on water availability, water resources development and management infrastructure, and water quality status. Water inflows were shown to have significantly reduced. The water quality status has deteriorated and by 2014 had reached alarmingly high levels, especially from Basra to the river mouth. The causes that could explain the steadily increasing water salinity varied from location to another. These include: decreased water quantity and quality (from the main and subsidiary water sources); seawater intrusion under tidal influences; poorly regulated localized water withdrawals; polluted return flows (from irrigation and several other wastewater discharge points); high evaporation rates; and occasional saline water discharges from the surrounding marshes. Analysis of intra-annual variability of salinity levels shows high spatiotemporal variability in the range of 0.2-40.0 ppt [or g kg-1; ×1.5625 µS.cm-1]. Similarities found in salinity dynamics were used to divide the river course into four distinct spatial units (R1-R4) to guide respective management actions (Chapter 4). Mean monthly salinity ranges of 1.0-2.0, 2.0-5.0, 1.0-12.0 and 8.0-31.0 ppt were observed for stretch R1 (Qurna to Shafi), R2 (Makel to Abu Flus), R3 (Sehan to Dweeb) and R4 (Faw near the estuary), respectively. Correlating longitudinal and vertical salinity measurements provided the initial estimates of the extent of inland seawater excursion into the SAR estuary. To achieve a more physically based estimate of the seawater intrusion distance, a predictive model was developed that takes account of the specific tidal, seasonal and discharge variability and geometric characteristics of the SAR (Chapter 5). Seawater excursion was simulated analytically using a 1-D analytical salt intrusion model with recently updated equations for tidal mixing. The model was applied under different river conditions to analyse the seasonal variability of salinity distribution during wet and dry periods near spring and neap tides between March 2014 and January 2015. A good fit between computed and observed salinity distribution was obtained. Estimating water withdrawals along the estuary improved the performance of the viii model, especially at low