From hydrodynamic to hydrological modelling: Investigating long-term hydrological regimes of key wetlands in the Macquarie Marshes, a semi-arid lowland floodplain in Australia Li Wen a,⇑ , Rohan Macdonald b , Tim Morrison c,1 , Tahir Hameed b , Neil Saintilan a , Joanne Ling a a Science Division, NSW Office of Environment and Heritage, Sydney, Australia b NSW Office of Water, Department of Primary Industries, Sydney, Australia c DHI Water and Environment Pty Ltd., Sydney, Australia article info Article history: Received 28 October 2011 Received in revised form 5 June 2013 Accepted 10 July 2013 Available online 24 July 2013 This manuscript was handled by Konstantine P. Georgakakos, Editor-in-Chief, with the assistance of Michael Brian Butts, Associate Editor Keywords: MIKE FLOOD IQQM Hydrological indicators Wetland restoration Flow-ecology relationship summary The Macquarie Marshes is an intermittently flooded wetland complex covering nearly 200,000 ha. It is one of the largest semi-permanent wetland systems in the Murray–Darling Basin, Australia, and portions of the Marshes are listed as internationally important under the Ramsar Convention. Previous studies indicate that the Marshes have undergone accelerated ecological degradation since the 1980s. The eco- logical degradation is documented in declining biodiversity, encroaching of terrestrial species, colonisa- tion of exotic species, and deterioration of floodplain forests. There is strong evidence that reduction in river flows is the principal cause of the decrease in ecological values. Although the streams are relatively well gauged and modelled, the lack of hydrological records within the Marshes hampers any attempts to quantitatively investigate the relationship between hydrological variation and ecosystem integrity. To enable a better understanding of the long-term hydrological variations within the key wetland sys- tems, and in particular, to investigate the impacts of the different water management policies (e.g. envi- ronmental water) on wetlands, a river system model including the main wetland systems was needed. The morphological complex nature of the Marshes means that the approximation of hydrological regimes within wetlands using stream hydrographs would have been difficult and inaccurate. In this study, we built a coupled 1D/2D MIKE FLOOD floodplain hydrodynamic model based on a 1 m DEM derived from a LiDAR survey. Hydrological characteristics of key constituent wetlands such as the correlation between water level and inundation area, relationships between stream and wetlands and among wetlands were estimated using time series extracted from hydrodynamic simulations. These relationships were then introduced into the existing river hydrological model (IQQM) to represent the wetlands. The model was used in this study to simulate the daily behaviours of inflow/outflow, volume, and inun- dated area for key wetlands within the Marshes under natural conditions and recent water management practices for the period of July 1 1991 to June 30 2009. The results revealed that the recent water man- agement practices have induced large changes to wetland hydrology. The most noticeable changes include the dramatic reductions in high flows (i.e. flows with less than 25% exceedence, reduction ranges from 85% to 98% of the high flow peak depending on the location), areal inundation extent (ranging from 13% to 79% depending on climatic conditions), and flow rising/falling rates (over 90% for high flows). Our analysis also highlighted that the impacts of water management practices on some of the flow variables for wetland habitats contrasted with those for instream habitats. For example, we did not find any evi- dent alterations in the low flows (i.e. 75% exceedence) attributable to water management. Crown Copyright Ó 2013 Published by Elsevier B.V. All rights reserved. 1. Introduction There is an increasing recognition of the ecological and eco- nomic values and services of wetlands within the lowland flood- plain landscape (Ehrlich and Ehrlich, 1992; MEA, 2005; Duranel et al., 2007; Acreman and Ferguson, 2010). Notwithstanding, the losses and degradation of wetlands have been exceptional during the last two centuries (MEA, 2005; Dudgeon et al., 2006). For 0022-1694/$ - see front matter Crown Copyright Ó 2013 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhydrol.2013.07.015 ⇑ Corresponding author. Address: Science Division, Office of Environment and Heritage, NSW Department of Premier and Cabinet, 59-61 Goulburn Street, Sydney 2000, Australia. Tel.: +61 (02) 9995 5054; fax: +61 (02) 9995 5924. E-mail address: li.wen@environment.nsw.gov.au (L. Wen). 1 Current address: Regional Operations, Office of Environment and Heritage, NSW Department of Premier and Cabinet. 10 Valentine Ave, Parramatta NSW 2150, Australia. Journal of Hydrology 500 (2013) 45–61 Contents lists available at SciVerse ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol