1 Canal Seepage ESHMC 8 January 2008 B. Contor

2 Outline Current treatment of Canal Seepage Review of Recharge Tools PEST Possibilities Implications of Canal Seepage Possible alternate methods

3 Current representation: A handful of canals are explicitly represented –long stretch of leaky canal not contiguous with irrigated lands –North Side laterals where source map indicated GW irrigation but hydrographs indicated SW seasonality

4 Current representation: For other canals, we assume leakage is spatially distributed across irrigated lands –density of laterals is high relative to cell size –laterals expected to be leakier than main canals ratio of Q/wetted perimeter maintenance periodic drying

5 Current representation: Seepage rates are based on two rounds of canal-manager interviews –Aberdeen-Springfield canal: Annual seepage rates from company analysis of data –limited data from a 1950s study of a short reach of another canal –no other hard data –except for Aberdeen-Springfield, seepage rate estimates were held constant throughout calibration period

6

7 The User hands the GIS tool... Map of model cells Map of canals –each canal belongs to an irrigation entity –each canal has a unique identifier Table of seepage rates (fraction of diversions) –unique value for each canal, for each stress period Diversion data for each entity

8 GIS tool hands FORTRAN tool.. Table of diversions for each entity, for each stress period Canal data file –list of cells that have leaky canals –canal/entity association –list of leakage fraction by canal and stress period

9. cnl file Canal seepage data... Row and column of cells covered by the first canal Proportion of diversion volume leaked from each canal (proportion in same order as canals are listed) Source of data 1 - new data 0 - no data -1 - use previous data Number of leaky canals Entity ID Number of cells that the first canal covers (Stolen from May Training)

10 FORTRAN Tool calculates... Seepage volume for each cell, for each stress period –Every drop of water imputed to canal leakage is subtracted from water applied to irrigated lands –Net effect on water budget = zero

11 What does this mean? Tools allow a unique seepage to be applied to each canal, for each stress period Changing canal seepage requires no change of recharge tools

12 PEST Possibilities

13 Add multiplier(s) for canal leakage (requires minor modification of FORTRAN & GIS tools) Potential PEST adjustment of canal seepage

14 Potential PEST adjustment of canal seepage Also, theoretically we could teach PEST to monkey with *.cnl file, but number of parameters gets BIG fast...

15 Implications

16 Three Important Implications of Canal Leakage Canal leakage affects spatial distribution but not magnitude of recharge

17 Options

18 Options Retain status-quo

19 Options More canals –hyd2mil GIS data & aerial images

20 Options Fancy algorithm –seepage = f (water temperature, soil type, wetted perimeter, head in canal, vegetation, head in aquifer if interconnected, maintenance schedule, wetting/drying freq, time since wet-up, presence of check structures....)

21 Questions Where do we get the data? What do we gain by the effort? Is this the best place to spend our resources? Can we agree on an approach? Will it be defensible?

22 Courtesy Rick Raymondi - look closely!