AERIAL RECONNAISSANCE OF OBSERVED SEDIMENT IN ROBINSON
BAYOU
John M. Sibley, Department of Earth Sciences, University of South Alabama, Mobile,
AL 36688. E-mail: jms903@jagmail.southalabama.edu.
Sedimentation buildup in Dog River has been an issue that has plagued the river
system since the U.S. Army Corp of Engineers began dredging the river in the 1870’s. In
the 1990’s, the city of Mobile began measures to address the sediment getting into the
river. Now almost 20 years later sedimentation remains a problem. Aerial photography
from remote controlled aircraft (UAV) can be used to check the conditions of the creeks
and streams that feed into Dog River. Robinson Bayou and Moore Creek were chosen for
over flights because they are located in the middle section of Dog River. Robinson Bayou
has not seen any construction in recent years while there has been construction in the area
that feeds Moore Creek. The results found that there was more sediment in Robinson
Bayou than in Moore Creek. Subsequent flights revealed the source of the sediment
confirming the usefulness of the UAV for surveillance.
Keywords: Dog River, sedimentation, remote controlled aircraft
Introduction: Sediment runoff in Dog River has been a problem that has plagued the river for
years. Records as far back as 1870 show that sediment building up in the river has been a
continuous issue for boaters navigating the river (Annual, 1871). Dredging has always
been conducted in the river due to the sediment buildup. This costs the government a lot
of money to have a dredge come in and deepen the river (Analytical and Topical Index
1881). Dog River, located in Mobile County, Alabama, is a tidal river that has a
relatively small watershed when compared to other rivers such as the Mobile River and
the Alabama River. The main issue the river has is all the sediment that comes from new
construction and existing neighborhoods and commercial areas. Sediment entering
creeks, streams, rivers, and lakes is the nation’s number one water pollution problem
according to the US Environmental Protection Agency. (EPA, 2003) The sediment from
new construction enters the waterway when protective measures such as silt fences, straw
wattles, erosion control blankets, turbidity barriers, and coir mats are not used as a barrier
to keep the sediment out of the waterways. When temporary barriers and silt fencing are
not implemented this runoff pollutes the creeks that then carries the sediment into the
main river.
Robinson Bayou has an issue with sediment pollution. Existing residential and
commercial properties drain off lawn and roads directly into the bayou. A sub-basin of
Dog River, the area that runs off into the bayou borders Mobile Downtown Airport to the
north and east and Gill Road to the south. In this area new construction is going in to
areas that have traditionally been wooded areas. This leads to an increase in sediment
runoff if the developer does not deploy basic measures to keep the soil from eroding off
when it rains. Robinson Bayou’s slow to no current allows the sediment to accumulate in
the bayou and restricts the water flow with the shallower depth. With the lack of water
velocity the sediment will sink in place and the water depth will decrease. The waterway
becomes impassible to vessels (Dean, 2005). Previous student researchers at the
University of South Alabama have experimented with using remote sensing from
satellites and general aviation aircraft to document runoff in the Dog River watershed
(Carver, 1998). But these past images don’t provide a close up image of what is
happening at the surface.
Using remote controlled aircraft, commonly known to hobbyist as an unmanned
aerial vehicle (UAV), for aerial photography has only recently become a cheaper
alternative to using real airplanes and helicopters. The UAV is commonly mistaken for its
commercial counterpart known as a Drone. With the high price of fuel driving the
operation cost upwards of $1500/hour, people and companies are looking to cut that cost.
By utilizing the UAV, aerial photography is possible closer to the ground than airplanes
are allowed to be. Plus with the invention of the Quadcopter, the UAV is able to hover
over an area to take detailed pictures and video. This clearly gives a distinct advantage
over relying on Landsat imagery taken from space. Quadcopters are now able to follow a
fixed GPS route ensuring that the route and imagery can be repeated. Landsat data for the
last 30 years can be used to further detect any changes that have occurred in the study
area. The Landsat data provides a set reference that video from the UAV can be
compared against. (Pritchard, 2005)
Study Area:
Figure 1. The middle section of Dog River houses the Moore Creek and Robinson Bayou sub-basins.
The study area is Robinson Bayou and the mouth of Moore Creek, both located in
the middle section of Dog River (Fig. 1). Both sub-basins are known for trash buildup
and sediment runoff from local construction. Robinson Bayou is bordered by Dauphin
Island Parkway to the east.
Research Question:
Can a UAV be used to locate runoff plumes in Robinson Bayou or Moore Creek
of sediment from new construction or existing structures?
Methods:
An UAV (Fig. 2) was rented from
hobbyist Daniel Thames. The aircraft is battery
operated and is a kit sold commercially on the
internet. The onboard camera is the
commercially available GoPro Hero 3+. The
Figure 2. Remote Control Aircraft (UAV)
camera has 1080p HD resolution allowing for
clear imagery to be taken of the area below. The image is transmitted to the ground
controller by a short range video transmitter. Areas of Robinson Bayou were flown over
for the purpose of locating areas that have visible sediment that cannot be easily seen
from eye level. By using the UAV, the camera was able to access would be available in
an area that a commercial aircraft would not be able to see, such as low over a
neighborhood or an area with power lines.
Two sites were chosen and photographed with the aid of an UAV. The site that was selected as Site A was Robinson Bayou (Fig. 3) and a second site that was selected was at the mouth of Moore Creek as Site B (Fig. 4). Both sites are in the middle section of Dog River and have a fair amount of water that drains from them. The Montlamar Canal feeds directly into Moore Creek from West Mobile. If there was construction runoff from work being done, it would be visible in the aerial photography of Moore Creek. Figure 3. The mouth of Robinson Bayou at Dog
River looking north
Figure 4. The mouth of Moore Creek at Dog
River looking west Results:
The aerial photography from the UAV showed a surprising result. The water color in Robinson Bayou was a light brown color (Fig. 3) that is indicative of sediment in the water. The water at Moore Creek was observed to be a dark color that is indicative of water free of sediment. This was surprising as there has not been new construction in the Robinson Bayou watershed that would lead to the plume observed from the aircraft. A follow-­‐up flight was conducted along Robinson Bayou where the bayou crosses under Dauphin Island Parkway. Figure 5. Looking south along Dauphin Island
Parkway
Figure 6. Looking east at the dirt pit from
Robinson Bayou
A large dirt pit was observed in the second flight on property that borders Robinson Bayou at Dauphin Island Parkway (Fig. 5). Aerial photos show where a silt fence is installed along the edge of the dirt pit (Fig. 6). Analysis shows that the loose soil is getting thru the fencing and into the bayou. Figure 7. Looking north over the dirt pit towards Dauphin Island Parkway
The remote controlled aircraft was able to visually identify that there was sediment entering Robinson Bayou (Fig. 7). The dirt pit observed on the aerial flight is the most likely source of the sediment in Robinson Bayou. I contacted the Alabama Department of Environmental Management [ADEM] to request any permits that had been issued for dirt pit sites in Robinson Bayou. Scott Hughes, Public Relations Director for the Permits and Services Division informed me that they did not have any on file. Conclusion: By using the remote controlled aircraft, the overall cost of the flight is low compared to having to rent a full size aircraft, hiring a pilot, and the fees involved with the plane. With fuel prices at an all time high, using a full size aircraft such as the Cessna 172 is no longer affordable. The cost alone for using an airplane begins around $2,000 per flight. A DJI Phantom Quadcopter is sold in stores and on the internet with a price point beginning at $499. The DJI Phantom has the ability to follow a pre-­‐programmed GPS path to ensure that the flight can be reproduced. Combine it with a GoPro Action Camera for $199, the total operating cost is kept to $700. There are several possible follow-­‐up projects that be done after this project. A project that could yield excellent results would be to take core samples in Robinson Bayou to determine how much sediment has accrued. I followed up with ADEM and was told that they would be looking into my findings. Special Thanks:
The author of this paper would like to thank Linda Piper of Allen Ct, Mobile, AL
and Dennis Thomas of Riviere Du Chien Loop, Mobile, AL for allowing access through
their property to Dog River. The author would also like to thank Daniel Thomas, a
student at the University of South Alabama, for his piloting time and the use of his UAV.
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