Effect of Land Use on Sediment Transport in Streams Draining Coastal Watersheds

Moussa Albert Siri Mentor: Dr Wilfred Wollheim

TRiO/McNair Undergraduate

Research Program 2016

Departement of Natural resources and the environment

Introduction

Problem: There is an increasing change in sediment deposition in coastal environment

Sediment input in coastal area is via streams and rivers

Sediment input in streams and rivers is impacted by:-Land use-Stream slope (low in many coastal watersheds)-Flow conditions (most important)

Introduction

Goal: understand variation in total suspended sediment (TSS) due to land use and flow in streams draining to an important estuary.

Hypothesis: Urban and agricultural land use will add more sediments into streams than least disturbed lands (forested lands) particularly during storm events.

Background

-Stream transport capacity: high at steep slope and decrease as slope decreases (Armanini et al. 2015, and Brandt S. A. 2000).

-Agricultural and urban vs. forested lands (Lenat and Crawford 1993, and Buck et al. 2003)

-Slope impacts stream power and its transport capacity (Yu et al. 2015).

Lanes Law: Stream power = Dischage (Q) x SlopeNote: in low slope, stream power ≈ discharge

Background

Connection to our study-study area with shallow slope (low impact on TSS)

-TSS more important in streams in urban and agricultural areas during storm events

-flow will mainly impact TSS particularly during storm events

Methodology

15 sites and at least 152 water samples filtered and weighed

-flow measurement couple times (record stage at each sampling)

MethodologyField work

-manual sampling every other week

-use of auto-samples during storm sampling

Methodology

Data analysis

Lab processing

-Sediment filtration

-Hobo's data download

Results (Base Flow Conditions)

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.040

5

10

15

20

25

f(x) = − 173.577968531272 x + 15.259875227239R² = 0.0631720611567915

Stream Slope (ft/mile)

TSS

(mg/

L)

TSS vs. Stream Slope: R2 value indicates that there is no correlation between TSS and the slope of the stream. As mentioned before, stream slopes are very shallow in the study area. They don't impact stream transport capacity. Slope is estimated using 10 and 85 method (ft/mile).

Results (Base Flow Conditions)

0 1 2 3 4 5 60

5

10

15

20

25

R² = 0.13469779974219

Basin Slope (30m DEM (%))

TSS

(mg/

L)

TSS vs. Basin Slope: R2 value indicates that basin slopes do not impact TSS concentration in streams.

Results (Base Flow Conditions)

15 20 25 30 35 40 45 50 550

5

10

15

20

25

R² = 0.147383695183229

Forest Cover (%)

TSS

(mg/

L)

TSS vs. Forest Cover: R2 value indicates also that there is no signifant correlation between TSS and forest cover. However, the presence of consecutive high TSS concentration at least forest cover areas suggest some support to the role of forest cover on TSS concentration in streams.

Results (Storm Flow Conditions)

TSS and Discharge vs. Time: This figure shows TSS vs. time (blue graph) and dischage vs. time (red graph) during storm of June 05, 2016. The figure shows a strong relationship between TSS and stream discharge during storm events.

2016-06-05 0:00 2016-06-05 12:00 2016-06-06 0:00 2016-06-06 12:00 2016-06-07 0:00 2016-06-07 12:00 2016-06-08 0:000

2

4

6

8

10

12

0

2

4

6

8

10

12

Time (hours)

TSS

(mg/

L)

Stre

am D

isch

arge

Q (L

/s)

Results (Storm Flow Conditions)

0 200 400 600 800 1000 1200 1400 1600 1800 20000

20

40

60

80

100

120

140

160

Discharge (L/s)

TSS

(mg/

L)

TSS vs. Discharge: Hysteresis graph indicates that the TSS concentration increases faster in the stream than the discharge at the beginning of the storm, but inversely, TSS decreases faster than the discharge at the end of the storm (Storm of June 05, 2016).

Results (Storm Flow Conditions)

TSS and Discharge vs. Time: This figure shows TSS vs. time (blue graph) and dischage vs. time (red graph) during storm of June 28, 2016. Here also, the figure shows a strong relationship between TSS and stream discharge during the storm events.

2016-06-28 12:00 2016-06-29 00:00 2016-06-29 12:00 2016-06-30 00:00 2016-06-30 12:00 2016-07-01 00:000.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

Time (2 hours)

TSS

(mg/

L)

Dis

char

ge Q

(L/s

)

Results (Storm Flow conditions)

TSS vs. Discharge: Hysteresis graph indicates that the TSS concentration increases faster in the stream than the discharge at the beginning of the storm, but inversely, decreases faster than the discharge at the end of the storm (Storm of June 28, 2016).

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

Discharge (L/s)

TSS

(mg/

L)

Conclusion

However, plot of TSS versus forest cover shows some support to the hypothesis (high TSS in least forest area, and low TSS in most forested area

Base flow conditions:

The results show no significant correlation between TSS and stream slope. There is no significant connection between TSS and basin slope either and also no between TSS and forest cover.

ConclusionStorm flow conditions:

Increase of TSS, due to storm event, is consistent with the hypothesis, but by itself is not sufficient to support or refute the hypothesis

-There is a strong correlation between flow level and TSS during storm events in agricultural/urban whatershed

-Storm event data, already collected from forested sites, are being processed. In order to test the hypothesis, these data will be used to compare land use impacts on TSS during storm events.

Acknoledgments!

-my Mentor Dr Wilfred Wollheim and his research team for their support during this research

-the McNair Program for giving me the opportunity to conduct this research

Thank you for being in this room to share my research!

-ESPCoR NEST project for its contribution to this proct

-Emily Balcom and Chris Cook for their precious help in the field

My acknoledgments go to:

-my family for its patient and understanding

-Armanini, A., Fraccarollo, L., & Rosatti, G. (2009). Two-dimensional simulation of debris flows in erodible channels. Computers & Geosciences, 35(5), 993-1006.-Buck, O., Niyogi, D. K., & Townsend, C. R. (2004). Scale-dependence of land use effects on water quality of streams in agricultural catchments. Environmental Pollution, 130(2), 287-299.-Lenat, D. R., & Crawford, J. K. (1994). Effects of land use on water quality and aquatic biota of three North Carolina Piedmont streams. Hydrobiologia, 294(3), 185-199.-Yu, B., Zhang, G. H., & Fu, X. (2014). Transport Capacity of Overland Flow with High Sediment Concentration. Journal of Hydrologic Engineering, 20(6), C4014001.-Brandt, S. A. (2000). Classification of geomorphological effects downstream of dams. Catena, 40(4), 375-401.a

References