Scott Brown, Mark Woyshner, and Barry Hecht

1. Sources and pathways of ground-water flow to canyon streams as inferred from dry-season baseflow conditions, Carmel River watershed, California Scott Brown, Mark Woyshner, and Barry Hecht

2. Outline • Study sites: • Lower Las Garzas and Pine Creeks • Proposed model of ground-water inputs • Methods of analysis: • Streamflow recession analysis • Stream surveys • Longitudinal measurements of specific conductance • Incorporating watershed disturbances • Implications for mitigation monitoring

4. Stream Characteristics • Deep granitic canyon with broad, flat, sedimentary ridge-tops • Channel morphology—step-pool or canyon pool-riffle architecture • Intermittent stream with some perennially flowing reaches • Alternating reaches of thick and thin cobble/ boulder alluvium overlying granitic bedrock • For Las Garzas, pools are relatively free of sediment due to dam upstream

5. Digital elevation model—lower Las Garzas Creek Carmel River Lower Las Garzas Creek Broad tributary uplands Source: USGS National Elevation Dataset

6. Aquifer Characteristics • Fractured-granitic, deep (regional) zone: consistent low-flow source related to permeability of discrete fractures • Shallow (local) zone: limited higher-discharging source responding to antecedent rainfall patterns and carry-over from wet years • Alluvial channel water: storage and mixing of remnant wet-season runoff and accretion flow sources

7. Streamflow Records • Compare baseflow recession patterns (flow persistance) from year to year

12. Baseflow Surveys • Delineate the extent of flowing reaches, isolated pools and dry segments at various times of the dry-down • Track the progression of stream dry-down

13. ©2004 Balance Hydrologics, Inc.

14. ©2004 Balance Hydrologics, Inc.

15. ©2004 Balance Hydrologics, Inc.

16. Water quality monitoring • Measure specific conductance to identify distinct ground-water sources and track trends stream profile • Provides a metric to use that is independent of sediment filling and easier to measure at ultra-low flow conditions

20. Natural watershed disturbances altering baseflow • Wildfire • Episodic high-flow events • Pool-sediment infilling/scour

22. Summary • The shallow aquifer system, especially in the side canyons, is an important source of carry-over baseflow following wet years • Streamflow recession analysis and stream surveys • The deep aquifer supports summer flows in the deepest portion of the canyon, in the driest times of the year, and during very dry years • Specific conductance

23. Conclusions • In this case, the need for careful description of hydrogeologic connection to streamflow is driven by habitat considerations, not for the more common searches for water, movement of contaminants, or locations to store contaminants. • Monitoring-based mitigation through multiple lines of evidence is more effective than flow-threshold or reference-year comparison-based mitigation in low-flow and intermittent streams, and more adaptive to future watershed changes