1. Overview Setback (Ref Point/Erosion Rate/Planning Horizon)
Dominant Coastal Processes
Winds
Waves
Storms
Human Alterations
Rio Grande River
Brazos Santiago Pass Jetties
Port Mansfield Jetties
Sand Management (Beneficial Use) BSP
Past &Present Shoreline Changes
1854/1867/1880 (late 1800s) (Natural State)
(Human Alterations)
(Sand Management)
Late 1800s (Full Period of Record)
Overview
Climate
Setback (Ref Point/Erosion Rate/Planning Horizon)
Scientifically valid *************
Socio-economic defensible
Broad stakeholder acceptance

2. Sand Management considerations
Four major Climatic zones
- southern part of the coast receives less rainfall, and has experienced prolonged droughts
the more humid northeast portions have a +12 inches/yr, in contrast to the semiarid south of -28 inches/yr.
- affects growth/development and viability of coastal vegetation that help hold sand in place within the beach/dune system
Sand Management considerations
(Dune Strategy)
(1)
(2)
(3)
(4)
Modified from (Morton 1994)

3. Dominant processes that shapes
WIND – WAVES
and storms
Dominant processes that shapes
the coast

4. Wave Rose Wind Rose Predominate wave direction Southeast (3-7ft)
SPI approx. shoreline orientation
Wave Rose
Wind Rose 5%
10%
15%
20%
25%
30%
Predominate wave direction
Southeast (3-7ft)
Predominant wind
direction
Southeast
(10-20 mph)
USACE WIS Hindcast
FROM
Threshold to move sand
~ 10 mph
average speed ~12 mph
FROM

5. ~8,000
truckloads
Predominate Littoral drift direction (south to north)
100,000 to 150,000 yd3/yr northward
Waves approaching from the southeast
Littoral means of or pertaining to the shore, and littoral drift is sand moved along a beach by a littoral current, a current carried by waves breaking at an angle to the shoreline and moving parallel to and adjacent to the shoreline within the surf zone.
This usually occurs in one direction as dictated by the prevailing wind.

6. Wind -Waves and STORMS

7. 1854-2011 Hurricane and Tropical Storms (44)
within 100 miles of Brazos Santiago Pass (

8. Ten major storms since 1960
that followed
westward track
Surge and wave heights are affected by the configuration and bathymetry of the ocean bottom.
Storm surge from Hurricane Allen were 8 to 12 feet instead of the 15 to 20 feet that would have been likely further north

9. analysis interpretation
Hurricanes (25) – avg  6.3 yrs
(157 yrs) 16
yrs
Arlene 1993-TS
Time intervals
&
analysis interpretation
Hurricane Allen
1980
Hurricane
Beulah
1967
Tropical Storms and Hurricanes (44)
Hurricanes (25) / Tropical Storms (19)

10. Setback (Ref Point/Erosion Rate/Planning Horizon)
Dominant Coastal Processes
Winds
Waves
Storms
Human Alterations
Rio Grande River
Brazos Santiago Pass Jetties
Port Mansfield Jetties
Sand Management (Beneficial Use) BSP
Past &Present Shoreline Changes
1854/1867/1880 (late 1800s) (Natural State)
(Human Alterations)
(Sand Management)
Late 1800s (Full Period of Record)
Climate
Setback (Ref Point/Erosion Rate/Planning Horizon)
Scientifically valid *************
Socio-economic defensible
Broad stakeholder acceptance

11. Beneficial Use of Dredged Material
Primary Man-Made Activities that have altered the movement of sand and therefore influenced the shoreline change
1) Reduced flow and sediment from Rio Grande to Gulf:
Falcon (1954)
Amistad (1969) Dams
and other land-use practices
2) Brazos-Santiago Jetties (1935):
North jetty (5,370 ft long)
South jetty (5,092 ft long)
3) Mansfield Pass ( ):
North jetty (2,300 ft long)
South jetty (2,270 ft long)
Beneficial Use of Dredged Material
Brazos Santiago Pass

12. and other land-use practices
1) Reduced flow and sediment from Rio Grande to Gulf
Reduction of flow and total suspended sediment from Rio Grande to the coast (-mid 1940’s)
Falcon (1954)
Amistad (1969) Dams
and other land-use practices

13. 2) Brazos-Santiago Jetties
1867 U.S. Coast Survey Map
Offset to the north
Jetties (1935):
-North jetty (5,370 ft long)
-South jetty (5,092 ft long)
Shoals Offset
to the north

15. 3) Mansfield Pass Construction (1957-1962) This channel, dredged
through the island and
lagoon in 1957

16. View looking south
View looking north across Mansfield Pass

17. Mansfield Pass
Predominate
littoral drift
direction
(south to north)

19. 1988 nearshore berms, 1997 began placing on the beach
4) Beneficial Use of Dredged Material -Brazos Santiago Pass
1988 nearshore berms, 1997 began placing on the beach
Example of needs north of SPI

20. Setback (Ref Point/Erosion Rate/Planning Horizon)
Dominant Coastal Processes
Winds
Waves
Storms
Human Alterations
Rio Grande River
Brazos Santiago Pass Jetties
Port Mansfield Jetties
Sand Management (Beneficial Use) BSP
Past &Present Shoreline Changes
1854/1867/1880 (late 1800s) (Natural State)
(Human Alterations)
(Sand Management)
Late 1800s (Full Period of Record)
Climate
Setback (Ref Point/Erosion Rate/Planning Horizon)
Scientifically valid *************
Socio-economic defensible
Broad stakeholder acceptance

21. (Human Alterations) (Sand Management) Changes over time:
4 periods of Analysis
(Natural State)
(Late 1800s) Avg Erosion Rate
The Shores to end of HWY 100 road ft/yr
The Shores to County line ft/yr
Brazos Island to Rio Grande ft/yr
(Human Alterations)
Avg Erosion Rate
The Shores to end of HWY 100 road ft/yr
The Shores to County line ft/yr
Brazos Island to Rio Grande ft/yr
(Sand Management)
Avg Erosion Rate
The Shores to end of HWY 100 road ft/yr
The Shores to County line ft/yr
Brazos Island to Rio Grande ft/yr
(Full Period of Record)
1800s Avg Erosion Rate
The Shores to end of HWY 100 road ft/yr
The Shores to County line ft/yr
Brazos Island to Rio Grande ft/yr

22. Setback (Ref Point/Erosion Rate/Planning Horizon)
Dominant Coastal Processes
Winds
Waves
Storms
Human Alterations
Rio Grande River
Brazos Santiago Pass Jetties
Port Mansfield Jetties
Sand Management (Beneficial Use) BSP
Past &Present Shoreline Changes
1854/1867/1880 (late 1800s) (Natural State)
(Human Alterations)
(Sand Management)
Late 1800s (Full Period of Record)
Climate
Setback (Ref Point/Erosion Rate/Planning Horizon)
Scientifically valid *************
Socio-economic defensible
Broad stakeholder acceptance

23. Setback (~ 300 ft) Reference Point (MHW) Ref Point (MHW)
Erosion rate (10-12 ft/yr)
Planning Horizon (based on a 30 yr avg mortgage)
Reference Point (MHW)
It is the seaward boundary of private and public property ownership;
It's a shoreline position slightly seaward of the high water line (wet/dry line on the beach) that is used to document shoreline change;
It represents the interface between water-driven sand transport and airborne sand transport;
Its easy for a surveyor to establish its location relevant to the property owners parcel position on the beach.

24. Questions Steve Underwood sunderwood@appliedcoastal.com 225-337-2365
Applied Coastal Research and Engineering, Inc.
Gulf Coast Regional Office, Baton Rouge
445 North Blvd, Suite 850
Questions
Steve Underwood