Runoff Analysis of the Watersheds“El Arroyo El Chilito” and “La Presa Bernardez”

Guadalupe, Zacatecas, Mexico

Nathan Lowe, Shawn Stanley and Jeffery Crump

The Problem

• Between the city of Zacatecas and a nearby town called Guadalupe, a significant amount of urbanization is taking place, which is altering the runoff of two small watersheds, “Arroyo El Chilito” and “la Presa Bernardez”.

• Due to the recent development, flooding has increased in frequency and magnitude. The pavement has caused the ground surface to become less permeable, so that precipitation accumulates on the surface rather than absorbing into the soil.

• As urbanization continues, this hazard is expected to escalate, a concern to those who are aware of the problem.

Data Needed

• Digital Elevation Model (DEM)

• Land use distribution

• Soil type distribution

• Precipitation

• Aerial photos and maps

Delineation of the Sub-basins

1. Import the DEM

2. Run TOPAZ (flow accumulation software)

3. Choose the outlet point for the basin

4. Run “Delineate Basins Wizard”

DEM Data

• 30-meter resolution

• UTM NAD 27 coordinate system

• Digital basin delineation by flow accumulation

La Presa Bernardez

El Arroyo El Chilito

Land Use and Soil Type Data• Digital images

from INEGI (National Institute of Statistics, Geography and Informatics)

• Superposition of land use and soil type polygons

• Association of permeability with polygons for infiltration calculations

Land Use

Soil Type

Precipitation Data

• Intensity-Duration-Frequency (IDF) curves from historical data

• Design storm:

• SCS Type II 2- or 24-hour distribution

SCS Type II 24-hour Temporal Distribution

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Time (min)

Cu

mu

lati

ve p

erce

nta

ge

of

rain

fall

(%)

Duration Intensity Depth2 hours 21.3 42.624 hours 3.9 93.6

Projected Flows• By modeling a

hypothetical expansion of urbanized areas, the average permeability of the watersheds further decreases.

• An additional analysis in HEC-1 and HMS was performed to reflect this change.

• Comparing the two scenarios, further development will increase peak flows by approximately 1.5 to 2 times the current flows.

Present Condition Future Condition% Urban Area 2.97% 61.53%Peak Flow (cms) 7.3 13.9Runoff Volume (1000 m^3) 26.7 54.0

5-Year, 2-Hour Storm Runoff for La Presa Bernardez (HMS)

Bernardez RunoffPresent vs. Future

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Time (min)

Ou

tflo

w (

cms)

Present Outflow

Future Outflow

HEC-HMS vs HEC-1

• Problems with computations

• Differences in calculations

Future Bernardez Runoff HydrographsHEC-1 vs. HEC-HMS

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Time (min)

Flo

w (

cms)

HEC-1

HMS

Hy-8 Culvert Analysis

Recommendations

• La Presa Bernardez– Reinstate the existing detention basin by controlling the

outflow with an adjustable gate.– Determine the basin volume necessary to effectively

delay and attenuate the peak flow through the outlet.– This will reduce the risk of flooding downstream for

design storm events.• El Arroyo El Chilito

– Clear the debris from the channel downstream of the highway.

– Determine if the channel is capable of conveying design storm flows.

– Use the abandoned area upstream of the highway as a retention basin.

Further Analysis Needed• HEC-RAS models of channels below outlets• Topographical surveys of detention basins above

outlets• Basin outlet analyses to size detention basins

based on headwater requirements

Questions?

Special thanks to Dr. Jim aka “Mascarita Divina”