Random walk forecast of urban water in Iran under uncertainty

There are two significant reasons for the uncertainties of water demand. On one hand, an evolving technological world is plagued with accelerated change in lifestyles and consumption patterns; and on the other hand, intensifying climate change. Therefore, with an uncertain future, what enables policymakers to define the state of water resources, which are affected by withdrawals and demands? Through a case study based on thirteen years of observation data in the Zayandeh Rud River basin in Isfahan province located in Iran, this paper forecasts a wide range of urban water demand possibilities in order to create a portfolio of plans which could be utilized by different water managers. A comparison and contrast of two existing methods are discussed, demonstrating the Random Walk Methodology, which will be referred to as the â On uncertainty pathâ , because it takes the uncertainties into account and can be recommended to managers. This On Uncertainty Path is composed of both dynamic forecasting method and system simulation. The outcomes show the advantage of such methods particularly for places that climate change will aggravate their water scarcity, such as Iran

Overcoming the joint probability problem associated with initial loss estimation in design flood estimation

Design flood estimation techniques currently used in Australia only partially account for the joint probability interactions between flood producing variables. The joint probability problem associated with initial loss estimation is particularly important. Failure to deal with it can introduce considerable bias into estimated flood frequency distributions for ungauged catchments. One solution to this problem is to use continuous simulation whereby a rainfall generation model is linked to a catchment water balance and flood routing model. This technique has been used to explore less complicated ways of overcoming the joint probability problem by allowing design rainfall obtained from Australian Rainfall and Runoff (ARR) to be directly converted into rainfall excess. This eliminates the need for assumptions regarding initial loss. A continuous simulation approach has been utilised here by means of a stochastic point rainfall model, coupled with a stochastic evaporation model and modified AWBM model. This enables the determination of the scaling required for the conversion of rainfall into rainfall excess. The technique is validated using a kinematic wave catchment runoff model and comparison with observed flood frequency curves. Through this method, the simplicity of the design flood estimation approach is retained by the use of rainfall excess frequency duration (REFD) curves instead of rainfall IFD curves. The REFD method has been calibrated and tested on a number of catchments in Australia. Presented here are the results from the Boggy Creek catchment in Victoria. The scaling of the ARR design rainfall required has been very similar across all average recurrence intervals and event durations. This should allow the approach to be extended to other catchments.http://www.eng.newcastle.edu.au/~ncwe/ncweAJWR/Vol7No2.ht

A point rainfall model for risk-based design

The point rainfall model presented extends previous work on event-based rainfall models and overcomes some of their shortcomings. The model uses event-based data and can be calibrated using rainfall data substantially affected by missing or corrupted values. Particular attention was given to adequately simulating extreme storm rainfall events for use in hydrological risk assessment. The model is capable of simulating the inter-event time, storm duration, average event intensity and intra-event temporal characteristics. Conditioning of the average event rainfall intensity on rainfall duration and time of year is a feature of the model. Rainfall events are disaggregated using a conditional random walk on a dimensionless mass curve. Pluviograph data in 6 min increments from three Australian capital cities (Sydney, Brisbane and Melbourne) was used to calibrate the model parameters. It was found that the constrained random walk parameters were almost identical for the three cities. The model was tested using statistics not used in its calibration and the simulated intensity–frequency–duration extreme rainfall statistics compared very favorably with observed values. In addition, simulated aggregated statistics compared favorably with observed statistics from 30 min to monthly durations. The simulated annual rainfalls significantly underestimated the observed variability for Brisbane and Sydney, whereas satisfactorily reproduced the Melbourne variability. An explanation is offered for these differences.Theresa M. Heneker, Martin F. Lambert and George Kuczerahttp://www.elsevier.com/wps/find/journaldescription.cws_home/503343/description#descriptio

The impact of extreme low flows on the water quality of the lower Murray River and lakes (South Australia)

The impact of extreme low flows on the water quality of the Lower Murray River and Lower Lakes (Alexandrina and Albert) in South Australia was assessed by comparing water quality from five sites during an extreme low flow period (March 2007–November 2009) and a preceding reference period (March 2003–November 2005). Significant increases in salinity, total nitrogen, total phosphorus, chlorophyll a and turbidity were observed in the Lower Lakes during the low flow period. Consequently, water quality guidelines for the protection of aquatic ecosystems were greatly exceeded. Principal Component Analysis, empirical and mass balance model calculations suggested these changes could be attributed primarily to the lack of flushing resulting in concentration of dissolved and suspended material in the lakes, and increased sediment resuspension as the lakes became shallower. The river sites also showed significant but more minor salinity increases during the extreme low flow period, but nutrient and turbidity concentrations decreased. The most plausible reasons for these changes were decreased catchment inputs and increased influence of saline groundwater inputs. The results highlight the vulnerability of arid and semi-arid lake systems to reduced flow conditions as a result of climatic changes and/or water management decisions.Luke M. Mosley, Benjamin Zammit, Emily Leyden, Theresa M. Heneker, Matthew R. Hipsey, Dominic Skinner and Kane T. Aldridg