John M Steed

Hurricane Flood Reduction Strategies
Check Dams in the Mulegé Watershed Area
Figure 2.1: Mulegé Bridge
Figure 2.2: Mulegé Bridge 2006 Hurricane John
John M Steed
Source: http://o.b5z.net/i/u/10025743/i//1115px-Mulege_Mission_Pano.jpg
Figure 1.1
Map of Mexico
Background:
Figure 1.2
Watershed Drainage Basins in Central Baja
Check Dam Characteristics and Benefits:
•  Utilized as a measure to control flooding and provide
water storage for irrigated agriculture.
•  Usually smaller than 15 meters high and do not
generally displace populations (Agoramoorthy, 2008).
•  Benefits include: sediment catchment, water storage,
groundwater recharge, water sources for animals, and
flood control (Ibid; Hooke, 2002).
•  Can significantly reduce the economic costs associated
with increases in flood events that are likely to worsen
with the progression of global warming (Valentin, 2005;
Hooke, 2002).
Maps:
Several maps have been created in ArcGIS to analyze the
Mulegé watershed region in terms of the terrestrial
viability for check dam installation. Through the use of
ASTER based slope analysis and visual analysis of
Landsat images, three areas of potential installation of
check dams have been identified. Figures 3.2 and 3.3
display potential locations of the dams by indicating
bottlenecks in highly sloped valley walls with a broad and
flat floodplain upstream. The inset 3D map in Figure 3.3
shows the potential water fill area that check dams would
inundate. Figure 3.4 displays the location of check dams
and their relationship to the greater watershed.
Findings:
• 
• 
64.5 square miles can be isolated with the
implementation of dams in these three areas of the
watershed (Figure 4.1).
Up to 25 percent of potential runoff can be isolated
(Figure 4.2).
The Central Baja region of Mexico is home to many dry drainage basins south of the Vizcaíno Desert (See Figure
1.2). The community of Mulegé is situated two miles upstream from the mouth of the Mulegé River at the Sea of
Cortez on a high flood plain in the middle of the Baja Peninsula (See Figures 1.1 & 3.1). The town has suffered three
hurricanes since 2006, which have inundated several sections of the town, destroying infrastructure and homes
(Beadle, 2010).
The narrowing of the valley as it enters the town of Mulegé at the bridge over Transpeninsular Highway 1 has an
intensifying effect on flood events (see Figures 3.1-3.3). This geological feature significantly raises the water level
and intensity before it channels out to sea (see Figures 2.1-2.3). Moreover, regular flooding has brought large
amounts of sediment into the mouth of the Mulegé River, which has lowered the depth of the river, and made
spillover more common (Erickson, 2009). In response to the increasing onslaught of flood events, the community
action group Al Resgaté de Mulegé has argued for the creation of a series of check dams in the tributaries that feed
the Mulegé River; they assert that this intervention would slow runoff and reduce potential flooding (Beadle, 2010).
Check Dam Limitations:
Environmental:
• 
• 
• 
• 
• 
Check dams can become inundated with sediment.
They prevent deposition of sediment further down stream and can reinforce erosion in large flood events.
They will do nothing to prevent flooding if they are full or become inundated in large flood events.
They limit the amount of water that will normally flow into ecosystems further down stream in small rain events.
Negative impacts of check dams on rivers include, “segmented longitudinal profile, alter[ed] sediment dynamics,
bed and bank stability, interrupt[ed] longitudinal movement of nutrients and aquatic organisms, [and] alter[ed]
passage of flood waves” (Wohl, 2006, p. 220).
Technical:
•  Calculating engineering for check dams is difficult to assess due to the unknown rate of discharge per event, the
energy capacity of the event, and the effect on releasing large sediment into the flow.
•  Failure of check dams can occur due to high-energy potential carrying slope materials and debris (Batalla, 1999).
•  Utilizing check dams for flood control is questionable without a deep understanding of local hydrodynamics.
Social:
•  Watersheds are a collective resource and must be managed accordingly.
•  In marginalized and poor communities, the expense and engineering necessary for this undertaking may be
beyond the scope of what is possible from the community, which could result in external control over local
resources.
•  It is necessary to ensure that women are an active part of the deliberation process; for example, income creation
through dam building may preferentially benefit males.
Figure 2.3: Mulegé Bridge 2009 Hurricane Jimena
http://www.gunsmoke.com/vacations/baja_2006/day11.html
Source: http://www.flyingjim.com/images/Bridge%20flood.jpg
Findings and Conclusions:
Check dams have the potential to be implemented in the
Mulegé area in order to reduce the negative impacts that
hurricane flood events produce in the region. Before this can
be determined several factors are necessary:
Source: http://motoged.smugmug.com/Landscapes/Mulege-Flood-0906/flood-3/125455980_5xJZR-M.jpg
•  Community deliberation regarding potential solutions and
their impacts on the community, including discussion of
alternative options for flood mitigation or adaptation
strategies.
•  Analysis of power dynamics within the community and
whether certain populations would be marginalized
through the process.
•  On site geologic, hydrologic, and engineering surveys to
determine the viability of check dam instillation.
•  Development of environmental impact assessments.
•  Development of partners to ensure the economic and
technical requirements could be fulfilled sustainably.
Although good intentions are at the heart of creating check dams,
the attempt to control a river system fundamentally changes the
structure of the system in ways that will have upstream and
downstream consequences (Wohl, 2006). Considerations need to
be made that will assess the consequences of check dam
implementation in Mulegé, whether this is an appropriate and
sustainable intervention, and whether there are better alternative
solutions to the problem of hurricane flooding.
Figure 3.2: Slope Analysis of Mulegé Watershed Area
Figure 3.3: Potential Sub-Watershed Isolation Area & 3D Model
Figure 3.1: Mulegé Watershed Area
Aster data retrieved from: http://demex.cr.usgs.gov/DEMEX/; Landsat data retrieved from: http://data.geocomm.com/catalog/MX/group149.html; Mexico and USA base map data retrieved from: www.diva-gis.org. Maps created in ArcGIS. Watershed statistics derived from ASTER data and compiled in Excel.
Total Watershed
Isolated Watershed
Area (SQ/MI)
263.3
64.5
Average Hurricane
Rainfall (1.8"/Day)
31,183,854 CU/M
7,634,182.4 CU/M
Estimated Jimena
Rainfall Peak in
Mulagé Region
(15"/Day)
259,865,448 CU/M
63,618,186 CU/M
Figure 4.1: Watershed Area and Runoff Volume
2%
15%
8%
75%
Figure 4.2
Check Dam Sub-Watershed
Percentage (Total Watershed=100%)
Figure 3.4: Catchment Isolation & Potential Check Dam Location