1. Sand motion and dust emissions September 28 and 29, 2005

2. Why is Sand Motion Important? Sand is a principal driver of dust emissions –high sand motion generally means high PM 10 emissions –when sand motion is suppressed, so are dust emissions There are practical means to measure sand motion on the playa surface DCMs are designed to capture sand

3. Outline Conceptual models of sand supply on the playa DCM sand motion relationships and mode of action Evidence for large-scale sand motion relationships on and around the playa Implications for DCM SCA identification and compliance criteria

4. Conceptual models of sand supply on the playa Cahill et al.: Proposed playa stabilization with sand fences, implying a functionally finite sand supply on the barren playa Gillette et al.: Hypothesized a functionally infinite supply of sand sized particles on the barren, Owens playa Mass-balance accounting of sand movement and storage across playa, applicable in variable playa contexts

5. Conceptual model assumptions New sand generation is proportional to entrained sand – it takes sand to make sand New sand is assumed to be entrained There is a maximum amount of sand entrainment for a given combination of wind speed and surface conditions (the wind can only carry so much sand)

6. Entrainment Sequestration New sand Entrained sand Free sand = (Initial + Settled) - Sequestered Entrained sand balance = (Import + Entrained free + Entrained new) – (Export + Settled) = 0, (plug flow, forces export of all entrained sand) Settling ExportImport Playa surface Free sand

7. Entrained sand Import and Export Entrainment and Settling Sequestration New sand Playa surface Free sand A series of sand balances

8. Source w/ local sand Source w/o local sand Downwind sinks Sinks downwind of sink Sources downwind of sinks Wind direction w/ sand initially on surface w/o sand initially on surface low sequestration rate and capacity high proportion of free sand entrained

9. Source w/o local sand Source w/ local sand

10. Source w/o local sand Downwind sinks Sinks downwind of sink Sources downwind of sinks Wind direction low initial sand flux low sequestration rate and capacity high proportion of free sand entrained high initial sand flux high sequestration rate and capacity low proportion of free sand entrained w/o initial sand on surface

11. Source w/o local sand Downwind sinks

12. Source w/ local sand Source w/o local sand Downwind sinks Sinks downwind of sink Sources downwind of sinks Wind direction high sequestration rate and capacity low proportion of free sand entrained low sequestration rate and capacity high proportion of free sand entrained low initial sand flux

13. Sinks downwind of sink Sources downwind of sinks

14. Apply at what scale? All scales applicable, but balance between internal and external influences shifts

15. Sand motion is the primary emissions driver. So, … How does sand migrate within DCMs? How ought this affect compliance criteria for DCMs? In addition to acknowledged meso-scale processes, do macro-scale patterns of sand sequestration and supply on Owens playa affect areas’ emission rates? If so, how ought this affect supplemental control area determination?

16. Evidence for large-scale sand motion on and around the playa

17. Currently, there is circumstantial evidence that the shallow flooding DCM in Zone 2 may have arrested the growth of the Keeler dunes. The District has observed that old landmarks, desert pavement surfaces and dead upland shrubs that were buried under the dunes have become recently exposed; this may be due to the lack of new sand from the lake bed that replenished the dunes before dust controls were implemented. The attainment demonstration modeling assumes that once the lake bed is controlled, the [Olancha] dunes will stop growing and the fine particles will be winnowed out.

18. Evidence for interdependent sand motion Data from full-scale, installed DCMs, unavailable during preparation of the 2003 SIP, is now available to help us better understand sand motion patterns –Sand motion independent of vegetative cover: Sand motion within MV after 2003* and in most SF  zero (regardless of coverage by moisture or vegetation) –SF crusts protected: Crusts formed within SF show little or no evidence of sand abrasion, even when sand motion is intense in neighboring areas

19. Evidence for interdependent sand motion Data from full-scale, installed DCMs, … –Whole DCM areas are not emissive: In general, emissions appear to halt virtually at DCM margins; the DCM areas affect sand motion and dust emissions not as many independent, small areas, but rather as large- scale assemblages of interdependent areas containing a range of altered playa conditions

20. Evidence for large-scale, interdependent sand motion on and around the playa Nearby, free sand sources appear to instigate emissions in neighboring areas Sand sources along margins of the playa are deflating Sand accumulates at DCM margins Free sand is minimized and not readily entrained in interior DCM areas, rendering these areas less emissive

21. How may patterns of sand motion on the playa be altered at completion 2003 SIP dust mitigation projects? Sand supply from construction activity will change or cease as playa heals New DCM areas will protect the most active 30 sq mi of playa surface and act as giant sand sinks Uncontrolled playa areas will have these DCMs as new neighbors These changes will influence playa emissivity –in compliant and non-compliant areas within the DCMs –outside of DCM areas on neighboring uncontrolled playa

22. Implications for SCA identification Playa is composed of interdependent areas, whose relationships Areas on the playa must be considered within the context of the whole DCA, the whole playa, and off-playa influences DCMs required by the 2003 SIP must take effect and construction scars must heal before emissions patterns on the playa created by the SIP can be known

23. Implications for DCM compliance criteria Areas within DCMs must be considered within the context of the whole DCM area Since mobile sand is depleted at DCM margins, DCMs are effective even when some of the interior area is barren and dry Acres within a DCM are not as vulnerable as open playa or DCM margins, so local physical protection is not as vital