THREE NOVELLAS: PAST, PRESENT AND FUTURE CONDITIONS OF THE SAN PEDRO RIPARIAN NATIONAL CONSERVATION AREA Mark A. Gonzalez National Riparian Service Team

Past, Present and Future Conditions of the San Pedro Riparian System Novella 1: Once Upon a Time – Holocene history of the SPRNCA Novella 2: Flower Power – Everything you needed to know about plants but were afraid to ask Novella 3: Making a Better Sponge – Processes that store and release water along the San Pedro River OUTLINE

Project Area San Pedro Riparian National Conservation Area International border to St. David SPRNCA boundary INTRODUCTION (from Hereford 1993)

NOVELLA I: ONCE UPON A TIME – HOLOCENE HISTORY OF THE SPRNCA

HOLOCENE SETTING Piedmont/Fan Inner Valley Basin Fill Basement Rock

HOLOCENE SETTING Inner Valley Pre-entrenchment Landforms Entrenchment Landforms

HOLOCENE SETTING Weik Ranch Mbr yrs BP (Qwk) Hargis Ranch Mbr yrs BP (Qha) McCool Ranch Mbr BP to AD 1880 (Qmc) Little Ice Age (AD ) paleosol Qwk Qha Qmc-B Qmc-A Qmc-B Teviston alluvium (Qtv) 7500 yrs BP 4000 yrs BP 2600 yrs BP 1900 yrs BP Historic Sources: Haynes 1987; Hereford 1993; Waters and Haynes 2001

HOLOCENE SETTING: M C COOL RANCH PALEOSOL 1 mi S Summers Wells Garden Wash ¼ mi N of Casa de San Pedro Boquillas Wash ¼ mi S of Boquillas Wash Qtv Qmc Qtv Qmc Qtv Qmc Qtv Qmc Qtv Qmc

 Physical Conditions  Little Ice Age (AD )  Low-energy environment  Shallow depth to water table  High organic-matter content (esp. from paleo-cienega)  Water storage and release patterns HOLOCENE SETTING: M C COOL RANCH PALEOSOL Qtv Qmc

 Biological Conditions  Widespread cienega formation  Herbaceous dominated communities PRE-ENTRENCHMENT CONDITIONS

Timing (1880s-1910s +/-, Hereford 1993)  Downstream initiation (1882, Contention area)  Upstream migration (1908 – Hereford Bridge)  Spread into and up tributary drainages PERIOD OF ENTRENCHMENT Post-entrenchment channel: Deep San Pedro River Pre-entrenchment channel: Shallow

 t 1 Stable channel  t 2 Downcutting  t 3 Widening  t 4 Aggradation CHANNEL EVOLUTIONARY SEQUENCE t2t2 t3t3 t 1 stable t 3 widening t 4 aggradation t 2 downcutting t1t1

SUMMARY Qwk Qha Qmc-B Qmc-A Qmc-B Sources: Haynes 1987; Hereford 1993; Waters and Haynes 2001  Stream valleys evolved naturally throughout the Holocene Period in response to climatic fluctuations.  Aggradation (valley filling) coincident with wet/cool periods and high water tables  Channel incision and sediment removal coincident with dry/warm periods

 t 1 Stable channel  t 2 Downcutting  t 3 Widening  t 4 Aggradation SUMMARY t2t2 t3t3 t 1 stable t 3 widening t 4 aggradation t 2 downcutting t1t1 Channel Evolutionary Sequence: SPR in ‘infancy’

NOVELLA II: FLOWER POWER -- EVERYTHING YOU EVER WANTED TO KNOW ABOUT PLANTS BUT WERE AFRAID TO ASK

PAST –PLANT COMMUNITIES Terrace Floodplain/Cienega Channel + Perennial Flow Obligate wetland plants: Hardstem and threesquare bulrush; flatsedge; cattail,

PAST –PLANT COMMUNITIES Terrace Floodplain/Cienega Channel Perennial (water-table < 20 ft depth) FACW plants: Sacaton; bunchgrass/shrub; mesquite (+/- dependent on fire regime)

PRESENT – PLANT COMMUNITIES Holocene Terraces Terrace Floodplain Channel Perennial Reaches Obligate, and facultative wetland species: hardstem and threesquare bulrush; cattail; spikerush; horsetail, and seepwillow

PRESENT – PLANT COMMUNITIES Holocene Terraces Terrace Floodplain Channel Intermittent Reaches Johnsongrass, Bermudagrass, seepwillow, and minor occurrences of hydric herbaceous species

PRESENT – PLANT COMMUNITIES Holocene Terraces Terrace Floodplain Channel Perennial Reaches Fremont cottonwood / Goodding’s willow; Baccharis, with lesser amounts of netleaf hackberry, mulberry, grama grasses

PRESENT – PLANT COMMUNITIES Holocene Terraces Terrace Floodplain Channel Intermittent Reaches Fremont cottonwood / Goodding’s willow; xeric woody shrub (AZ ash and walnut, hackberry) with tamarisk/; baccharis and herbaceous understory

PRESENT – PLANT COMMUNITIES Holocene Terraces Terrace Floodplain Channel Perennial Reaches Sacaton – Mesquite continuum Sacaton dominated with frequent fire Mesquite dominated with fire suppression

PRESENT – PLANT COMMUNITIES Holocene Terraces Terrace Floodplain Channel Intermittent Reaches Increase in woody shrubs and decrease in herbaceous plants Facultative plants more common than hydric plants

 Plants in and near the riparian zone ‘stratify’ themselves by:  Depth to water  Permanence / seasonality of water (i.e., Perennial vs. Intermittent flow) SUMMARY Holocene Terraces Terrace Floodplain Channel

NOVELLA III: MAKING A BETTER SPONGE – STORING AND RELEASING WATER

WATER STORAGE: BANKS (I) (IV) (III) (II) (I) I Standard Form II Ponded Form III Tributary Fan Form IV Adjustment Form

WATER STORAGE: BANKS When stage (water level) is high in the channel, water is forced (pushed by hydrostatic pressure) into the banks and stored in the floodplain alluvium. When stage falls in the channel, the hydraulic gradient is reversed and water flows out of the banks and into the channel to supply baseflow between high-flow events

WATER STORAGE: BANKS Ponded water moves out of channel and into banks during high stage. Stored water also moves down valley with the hydraulic gradient. (I) (IV) (III) (II) (I)

Floodplain recharge has greater surface area than channel-bank recharge alone. This permits more water to enter alluvial aquifer in short time. WATER STORAGE: FLOODPLAIN

WATER STORAGE: FLOODPLAIN ROUGHNESS To increase floodplain infiltration, Floodplain vegetation must decrease water velocity

Grazing closure in 1988 (< 25 years ago) has allowed riparian vegetation to establish and grow. VEGETATION RESPONSE View from Hereford Bridge: (left) circa mid-1980s (BLM); (right) 10 years later (photos by D. Krueper, BLM)

WATER STORAGE: TRAPPED SEDIMENT

WATER STORAGE: TRAPPED SEDIMENT AND ORGANIC MATTER

Pounds H2O in 100 Pounds of Soil lbs H 2 O 140 lbs H 2 O 100 lbs H 2 O 55 lbs H 2 O 33 lbs H 2 O Percent Organic Matter Water Holding Capacity of Soil Organic Matter (modified from Carpenter)

LOSS OF WATER STORAGE km Miles ft 4100 ft Inner Valley Pre-entrenchment alluvium West East V.E. = 100X Available water volume in SPRNCA pre-entrenchment alluvial aquifer (WV a ) composed of silt loam: WV a = (448 acres/mile X 40 miles) X 20 ft thickness X 1.7”/ft ÷ (12”/ft) WV a = 50,000 acre-feet Pre-entrenchment alluvial aquifer (with 3’ thick cienega soil on 3600 acres (1/5 of riparian area) and MODEST 5% organic matter): WV a = 50,000 acre-ft + (16,000 gallons X 5 X 3’ X 3600 acres) ÷ (325,851 gals./acre-ft) WV a = 50,000 acre-ft acre-ft = 52,650 acre-ft

LOSS IN WATER STORAGE km Miles ft 4100 ft Inner Valley West East V.E. = 100X Available water volume in SPRNCA for post-entrenchment alluvial aquifer (WV a ) composed of sand: WV a = (128 acres/mile X 40 miles) X 10 ft thickness X 0.9”/ft ÷ (12”/ft) WV a = 3840 acre-feet Post-entrenchment alluvium

CONTROLS ON PERENNIAL FLOW Hwy 92 Hwy 90 Hwy 82 4 Cottonwood 1 Palominas 2 Hereford- Kolbe 3 Hunter 5 Lewis Spr. 6 Escapule 8 Boquillas 7 Charleston 9 Fairbank 10 Depot 11 Tombstone 12 Smrs-Cnt’n 13 St David 14 Escalante Babocomari R. St David Reaches 9-10 Predominantly Intermittent Reaches 1-8 Predominantly Perennial

 Reaches 1-4 Perennial:  Underlain by restrictive silt- clay layers  Reaches 5-8 Perennial:  Gaining reaches with water upwelling on the east side of the silt-clay restrictive layer  Reaches 9-14 Intermittent:  Bedrock controlled or smaller basin contributions USA AZ MEX SN

West East Elevation, ft above sea level 3 miles

South Palominas Hereford Cottonwood Lewis Spring Charleston gage Boquillas Fairbank 3 Miles North Elevation (ft amsl)

SUMMARY: CHANGE IN WATER STORAGE km Miles ft 4100 ft Inner Valley West East V.E. = 100X Pre-entrenchment estimated available water storage: 50,000 acre-ft Post-entrenchment estimated available water storage: 4000 acre-ft Post-entrenchment alluvium

Bigger sponges store more water--Sponges get bigger as:  Vegetation covers riparian area  Vegetation slows stream velocity and enhances infiltration  Vegetation / organic matter is trapped in sediment Bottom Line: More vegetation = more water storage SUMMARY

Bigger sponges store more water--Sponges get bigger as:  Sediment accumulates and aggrades on floodplain  Floodplain widens  Floodplains are inundated  Tributary mouth fans (and beaver) pond water Bottom line: More deposition = more water storage SUMMARY

Continued improvement in riparian conditions is dependent upon seasonal timing of streamflow, adequate runoff volume and sediment load, and unrestrained floods. Factors that reduce runoff volume, increase salinity, change runoff seasonality, or reduce sediment loads are detrimental to the riparian community (Hereford, 1993). Protection of both the flow and the sediment regime of this river are crucial to its survival. SUMMARY