THREE NOVELLAS: PAST, PRESENT AND FUTURE CONDITIONS OF THE

SAN PEDRO RIPARIAN NATIONAL CONSERVATION AREA

Mark A. GonzalezNational 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 ValleyPre-entrenchment Landforms

EntrenchmentLandforms

HOLOCENE SETTING

Weik Ranch Mbr. 6500-4300 yrs BP (Qwk)

Hargis Ranch Mbr. 3500-2000 yrs BP (Qha)

McCool Ranch Mbr. 2000 BP to AD 1880 (Qmc)

Little Ice Age (AD 1450-1850) paleosol

QwkQhaQmc-B

Qmc-AQmc-A

Qmc-B

Teviston alluvium (Qtv)

7500 yrs BP4000 yrs BP

2600 yrs BP

1900 yrs BP

Historic

Sources: Haynes 1987; Hereford 1993; Waters and Haynes 2001

HOLOCENE SETTING: MCCOOL RANCH PALEOSOL

1 mi SSummers

WellsGarden Wash

¼ mi N of Casa de

San PedroBoquillas

Wash

¼ mi S of

Boquillas Wash

Qtv

Qmc

Qtv

Qmc

Qtv

Qmc

Qtv

Qmc

Qtv

Qmc

Physical ConditionsLittle Ice Age (AD 1450-1880)Low-energy environmentShallow depth to water tableHigh organic-matter content (esp. from paleo-cienega)

Water storage and release patterns

HOLOCENE SETTING: MCCOOL RANCH PALEOSOL

Qtv

Qmc

Biological ConditionsWidespread cienega formationHerbaceous 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

t1 Stable channel

t2 Downcutting

t3 Widening

t4 Aggradation

CHANNEL EVOLUTIONARY SEQUENCE

t2

t3

t1 stable t3 widening

t4 aggradationt2 downcutting

t1

SUMMARY

QwkQhaQmc-B

Qmc-AQmc-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

t1 Stable channel

t2 Downcutting

t3 Widening

t4 Aggradation

SUMMARY

t2

t3

t1 stable t3 widening

t4 aggradationt2 downcutting

t1

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/CienegaChannel +

Perennial Flow• Obligate wetland

plants: Hardstem and threesquare bulrush; flatsedge; cattail,

PAST –PLANT COMMUNITIES

TerraceFloodplain/Cienega

Channel

Perennial (water-table < 20 ft depth)• FACW plants:

Sacaton; bunchgrass/shrub; mesquite (+/- dependent on fire regime)

PRESENT – PLANT COMMUNITIES

Holocene Terraces

TerraceFloodplain

Channel

Perennial Reaches

Obligate, and facultative wetland species: hardstem and threesquare bulrush; cattail; spikerush; horsetail, and seepwillow

PRESENT – PLANT COMMUNITIES

Holocene Terraces

TerraceFloodplain

Channel

Intermittent Reaches

Johnsongrass, Bermudagrass, seepwillow, and minor occurrences of hydric herbaceous species

PRESENT – PLANT COMMUNITIES

Holocene Terraces

TerraceFloodplain

Channel

Perennial ReachesFremont cottonwood / Goodding’s willow; Baccharis,

with lesser amounts of netleaf hackberry, mulberry, grama grasses

PRESENT – PLANT COMMUNITIES

Holocene Terraces

TerraceFloodplain

Channel

Intermittent ReachesFremont cottonwood / Goodding’s willow; xeric woody shrub (AZ ash and walnut, hackberry) with tamarisk/; baccharis and herbaceous understory

PRESENT – PLANT COMMUNITIES

Holocene Terraces

TerraceFloodplain

Channel

Perennial ReachesSacaton – Mesquite continuum

Sacaton dominated with frequent fire

Mesquite dominated with fire suppression

PRESENT – PLANT COMMUNITIES

Holocene Terraces

TerraceFloodplain

Channel

Intermittent ReachesIncrease 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 waterPermanence / 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 FormII Ponded FormIII Tributary Fan FormIV 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

1 2 3 4 5

Pou

nds

H2O

in 1

00 P

ound

s of

Soi

l

40

80

120

160

200 195 lbs H2O

140 lbs H2O

100 lbs H2O

55 lbsH2O

33 lbsH2O

Percent Organic Matter

Water Holding Capacity

of Soil

OrganicMatter

(modified from Carpenter)

LOSS OF WATER STORAGE

kmMiles

0 0.5

0.5

1.51

1

4200 ft

4100 ft

Inner ValleyPre-entrenchment alluvium

WestEast

V.E. = 100X

Available water volume in SPRNCA pre-entrenchment alluvial aquifer (WVa) composed of silt loam:WVa = (448 acres/mile X 40 miles) X 20 ft thickness X 1.7”/ft ÷ (12”/ft)WVa = 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):

WVa = 50,000 acre-ft + (16,000 gallons X 5 X 3’ X 3600 acres) ÷ (325,851 gals./acre-ft)

WVa = 50,000 acre-ft + 2650 acre-ft = 52,650 acre-ft

LOSS IN WATER STORAGE

kmMiles

0 0.5

0.5

1.51

1

4200 ft

4100 ft

Inner ValleyWest

East

V.E. = 100X

Available water volume in SPRNCA for post-entrenchment alluvial aquifer (WVa) composed of sand:

WVa = (128 acres/mile X 40 miles) X 10 ft thickness X 0.9”/ft ÷ (12”/ft)

WVa = 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 Fairbank10 Depot11 Tombstone

12 Smrs-Cnt’n

13 St David

14 Escalante

Babocomari R.

St David

Reaches 9-10 Predominantly Intermittent

Reaches 1-8 Predominantly Perennial

1

2

3

4

5

67

8

9101112

1314 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 contributionsUSA AZMEX SN

WestEast7500

2000

4000

6000

Ele

vatio

n, f

t ab

ove

sea

leve

l

3 miles

South

4000

3000

Pal

om

ina

s

Her

efor

d

Cot

ton

woo

d

Lew

is S

prin

g

Cha

rlest

on g

age

Boq

uilla

s

Fai

rban

k

3 Miles

North

Ele

vatio

n (f

t am

sl)

SUMMARY: CHANGE IN WATER STORAGE

kmMiles

0 0.5

0.5

1.51

1

4200 ft

4100 ft

Inner ValleyWest

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