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Water savings from investments in infrastructure

Water savings from investments in infrastructure. Mac Kirby, Mobin-ud-Din-Ahmad, Zahra Paydar, Akhtar Abbas and Tariq Rana. Outlook 2011, Canberra 2 March 2011. Key messages.

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Water savings from investments in infrastructure

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  1. Water savings from investments in infrastructure Mac Kirby, Mobin-ud-Din-Ahmad, Zahra Paydar, Akhtar Abbas and Tariq Rana Outlook 2011, Canberra 2 March 2011

  2. Key messages • Others, including the Productivity Commission and various natural resource economists, have commented that infrastructure improvements are likely to be less efficient and effective than buy-backs at recovering water for the environment • Here I address how much water could be saved anyway? • I will mostly comment on the physical aspects with some passing comments on economics The key messages are: • that there is great uncertainty about how much water can be saved.... • .... but it is unlikely to make more than a modest contribution to what we aspire to return to the environment (or save for irrigation) • Corollary: careful accounting of savings is required for investments

  3. Adding up potential savings • I will mostly look at infrastructure (off-farm), but will also make some passing comments about potential savings on-farm • Bottom up: looking at particular case studies and extrapolating • Top down: looking at the big picture across the MDB and partitioning water into used, “lost” and recoverable water • First, a little bit of process... I want to have a quick look at what really is “lost” water, and what savings are

  4. True losses Evaporation • Evaporation is a true loss (but we want evaporation from rivers!) • Seepage / leakage are true losses only if they go somewhere we can’t use - eg salty groundwater • Seepage / leakage to fresh groundwater or a river are available for re-use in irrigation or the environment Canal River Seepage leakage Flow returning to river

  5. True losses Evaporation • Evaporation is a true loss - but we want evaporation from rivers! • Seepage / leakage are true losses only if they go somewhere we can’t use - eg salty groundwater • Seepage / leakage to fresh groundwater or a river are available for re-use in irrigation or the environment Canal River Seepage leakage Flow returning to river A leaky canal (CSIRO study), not far from a river - return flows unknown

  6. True losses and potential savings Evaporation • Evaporation is a true loss - saved by: • piping canals (up to 100 % saving) • re-aligning irrigation system layout with shorter systems (< 100%) • some small savings also achievable through operations (running systems full) (<< 100%) • Seepage / leakage, if true losses, can be saved by: • piping canals (up to 100 % saving) • Lining canals (< 100%) • re-aligning irrigation system layout with shorter systems (< 100%) • some small savings also achievable through operations (running systems full) (<< 100%) • Message: not all savings measures are 100 % effective Canal River Seepage leakage Flow returning to river More expensive

  7. How important are return flows? On-farm Off-farm • Some rough figures • Message: return flows could be a significant fraction of seepage / leakage • 2nd message: we don’t really know; there are few (no?) quantitative studies Evaporation 65 80 100 Seepage ? 9 ? 9 ? 10

  8. The Pratt study in the Murrumbidgee • Suggested that perhaps 300 GL annually could be saved in the Murrumbidgee  ?? 1,500 GL basin-wide But... • 70 GL was from river evaporation - are we really going to save that? • 130 GL was from seepage and evaporation from supply and storage systems of the MIA and CIA... • ... of which 42 GL was seepage from 500 km of MIA canals... • but... MIL’s own figures give ~ 31GL for total 2,500 km of canals • So maybe seepage estimate is too high • And anyway, some is a return flow - it’s not lost • 100 GL is on-farm • Some necessary as a leaching fraction to prevent salt build-up in the soil • Some is a return flow So... • Total recoverable losses are unlikely to be more than 1/3 total ( ?? 500 GL) • Economically recoverable even less

  9. A top down calculation, off-farm components Diversions 8500 • Southern MDB diversions from MDBA water audit reports • 80 % delivery efficiency (ANCID) • Metering errors based on Hydro Environmental (6.8%) and GWM (10%) • Seepage and leakage as a fraction of losses based on Khan, Douglass, MIL • Unaccounted flows by difference, but also from MIL • Return flows estimated at 10 % of diversions across MDB (van Dijk) • Real savings unclear, but unlikely to be much Field delivery 6800 Losses 1700 Evaporation escapes unaccounted 500-700 Meter errors ~700 Seeps leaks 300-500 For use Return flows ? Potential savings <500 Not Economic ? Real savings ?

  10. Conclusions Key messages: • there is great uncertainty about how much water can be saved.... • .... but it is unlikely to make more than a modest contribution to what we aspire to return to the environment (or save for irrigation) • Corollary: careful accounting of savings is required for investments - eg assessment of return flows • Delivery efficiency improvements may be desirable on other grounds, such as a better managed system, more resilient to drought

  11. http://www.csiro.au/org/HealthyCountry.html Prioritising water for irrigation and the environment project funded by CSIRO Water for a Healthy Country

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