Particle Size Analysis of Two Adjacent Watersheds

By Jessica Kashian

Mentor: Tobias Finke

Background Information

Increase in Urbanization in the Southwest

Stress on Watersheds by decrease infiltration rates causing increased surface runoff which can lead to flooding and costly water infrastructure for prevention

Studying this phenomenon allows us to quantify effects of urbanization on infiltration rates

This would enable city planners to make more informed decisions on flood prevention strategies in new housing developments

Study Area: Ft Huachuca and Sierra Vista, AZ

Objectives

• Analyze Soil Samples for Particle Size Distribution • Statistical Analysis to determine whether there are

differences between two watersheds• Investigate the relation between Particle Size Distribution

and Infiltration

Research Questions: Are the particle size distributions different between the

watersheds? Can differences in infiltration capacities be explained by

particle size distribution of the soil?

Methods

20 Soil Samples Collected from each Watershed

Eliminate Carbonates by pretreatment of the Soil Samples

Methods

•50 grams of each treated Sample is used in Hydrometer Readings •Hydrometer: measures density of soil solution

•Measurements were converted to sand, silt and clay fractions

Results and Discussion Are the particle size distributions different between watersheds?

Sand Silt Clay

Statistical Comparison of Particle Fractions for Both Watersheds

t-Test DF Prob > (t)

4.546 38 <.0001

t-Test DF Prob > (t)-1.86939 0.0692

t-Test DF Prob > (t)-7.72839 <.0001

FH

FHFH

LT

LT

LT

Results and Discussion Can differences in infiltration capacities be explained by

particle size distribution of the soil?

Infiltration vs. Modeled Infiltration

y = x + 2E-13

R2 = 0.34690

5

10

15

0 5 10 15

Ksat in mm/hr

Ks

at m

od

ele

d in

mm

/hr

Ksat / Modeled Ksat

Linear (Ksat /Modeled Ksat)

MAD = 2.01Y= 0 +1X

R2= 0.35

Conclusions

Higher percentages of clay in developed area

Lower percentages of sand in the developed area

35% of the Infiltration values could be explained by particle sizes

Acknowledgements and Special Thanks

Susan Moran Rae-Landa Gomez-Pond Chandra Holifield Collins Jeff Kennedy Kevin Loeffelmann William Emmerich