1 October 2003
(2) The average precipitation was calculated to be 8.28 cm/year. These data, coupled
with the image data, established the inundation frequency to be 51% of the time. This sug-
gests that the playas are inundated, on average, every other year.
e. Conclusions. Results indicate that ponding that persists 16 days or longer occurred
approximately every other year. The average precipitation needed to initiate ponding is es-
timated at 8.29 cm. Duration of ponding was shown to range from 1 to 32 weeks, with a di-
rect relationship between length of inundation and total seasonal rainfall. Playa inundation,
duration, and frequency can be determined from precipitation data and satellite imagery.
The authors suggest the addition of contributing factors such as soil type and geometry may
lead to a more robust hydrologic model of the playa system. A thorough understanding of
the playa hydrologic regime may one day lead to new land use regulations.
Point of Contact: Robert Lichvar, Phone: (603) 634-4657
6-10 Case Study 8: An Integrated Approach for Assessment of Levees in the
Lower Rio Grande Valley
Subject Area: Engineering.
Purpose: To detect weak areas within levees prior to flood events.
Data Set: LIDAR.
a. Introduction. A series of levees were constructed along the Lower Rio Grande in
Texas and Mexico in the 1930s. Local farmers, working with the county government, con-
structed the levee system to prevent flood damage to crops in low-lying areas near the river.
The levees were constructed of sediment and soil materials obtained locally. The Federal
government later completed the levee system in the 1940s and continued expansion and re-
pairs through the 1940s. The US Army Engineer Research and Development (ERDC),
working recently with the International Boundary and Water Commission, developed a GIS
database to catalog levee condition. Knowledge of levee conditions prior to a flood is help-
ful in determining where repair and rebuilding are necessary on these man-made structures.
A visual display of the levee and detail on the location of potential structural failure could
then be used to prioritize levee repair and reconstruction.
b. Description of Methods.
(1) This study maintained four primary objectives. The first was to survey the levee
system of the Lower Rio Grande River. The information compiled during the course of this
survey was organized into a GIS database. The second was to extensively evaluate levee
condition. The third was to compare the results of the airborne survey with those obtained
from ground-based surveys. This objective tested the validity of implementing a remote
sensing survey. Fourth, ground-truth locations were selected based on LIDAR data, and at
these locations soil and subsurface strata were mapped using a cone penetrometer.
(2) In the course of developing the GIS database, ERDC developed a 10-point crite-
rion for evaluating the condition of the levee system. Traditional geophysical tools were