Modelling water demand and trade on the Murray and lower Darling rivers

The Murray–Darling Basin is one of the largest river systems in the world. It supports a large community and is ecologically diverse. The Basin Plan is being implemented to restore the balance between consumptive uses and environmental health in the Basin. The socio-economic implications are a critical consideration in any change to this balance. Under the Basin Plan, considerable effort was invested into understanding how irrigation communities will respond under different water availability/management scenarios. This paper builds on this understanding by enhancing modelling approaches used in water resource planning to represent how irrigator's behaviour may change in response to new water management rules. The analysis uses a new demand model in the Source IMS river modelling platform. The amount of water available to an irrigator is the key modelled decision variable, impacting on crop areas and crop mix. The available water is dependent on carryover from last year, allocated water, planned trade of allocation and planned carryover into the next irrigation season. Prior to making a planting decision, the irrigator will review their water portfolio and make a decision on how much water they plan to trade (in or out) and how much water they plan to carry-over into the next season. The resulting available water is then used to make a decision on what area they will plant to different crop types each year. This logic represents the trading of water to support urban and permanent horticultural plantings in low allocation years. Conversely, allocation is traded to increase the area of annual cropping systems in years of high water availability. The irrigators water portfolio is reviewed as the season progresses. If they are likely to run out of water, a decision is made to either reduce irrigation intensity (ie go into survival mode), cut back the irrigated area or to buy additional water. Any surplus water could be sold. The approach is tested against available land use, water use and trade data on the Murray and Lower Darling rivers

Effects of Braiding on Tensile Properties of Four-Strand Human Hamstring Tendon Grafts

Background: Anterior cruciate ligament reconstruction is commonly performed with autogenous hamstring tendon grafts. Purpose: To ascertain the effects of braiding on ultimate tensile strength and stiffness of hamstring tendon graft. Study Design: Controlled laboratory study. Methods: Sixteen fresh-frozen semitendinosus and gracilis tendons were harvested from eight matched (right and left) human cadaveric specimens. Both sets of hamstring tendons from each matched pair were doubled, creating a four-strand graft. Grafts were then randomized so that one graft from each matched pair was braided and the other remained unbraided. The diameter of each graft construct was recorded. Grafts were tested to failure on a materials testing machine. Results: There were no significant differences in cross-sectional area before or after braiding. Fifteen of 16 tendons failed midsubstance; 1 failed at the lower clamp. Braiding reduced the initial tensile strength and stiffness of human hamstring tendon grafts in this study by 35.0% and 45.8%, respectively. Conclusions: Braiding may place the collagen fibers in a suboptimal orientation for loading that results in a weaker graft. We do not recommend the use of braiding if the strongest, stiffest initial graft is desired