The Effect of Urbanization on Surface Water Flows

 

A Study of West Houston

 

Term Project Final Report

 

 

Matt Harold

CE394K.2 – Surface Water Hydrology

Spring 2007

 

 

Table of Contents

 

Introduction

 

Buffalo Bayou Watershed Overview

 

Previous Studies

 

Data Collection and Analysis

 

Brief Conclusions

 

Acknowledgements

 

References

 

 

Introduction

 

Over the last 60 years the city of Houston has grown at a staggering rate. The city is currently the fourth largest city in the United State and Harris County is the third largest county in the US.  The footprint of Houston over the past 60 years has grown to cover most of Harris County. Approximately 25-35% of Harris County lies within the 100-year flood plain.

 

Urban structures have a direct effect on the volume of surface water discharged in an area through two routes. Primarily, urbanization provides a more efficient method for the collection and transportation of rain water, through the construction of roads, parking lots, and storm water collection systems. This increase in transportation efficiency coupled with an increase in impervious cover, lowering potential maximum storage and thus increased runoff values, creates a significantly different surface water system than seen in non-urban environments.

 

 

                                             Houston 1973: 412 mi2                              Houston 1992: 754 mi2

Figure 1: Developed Land Surface Cover

(http://pubs.usgs.gov/circ/2004/circ1252/)

 

The City of Houston, TX is no stranger to this concept. Over the course of the last 60 years they have observed first hand the devastating effect of urban growth on the surface water system of the area. Through the construction and maintenance of an elaborate system of runoff collection bayous the city has managed to turn a once swamp covered prairie into a viable city. But as the city grows and the demand for property close to the commercial centers increases the cities past is quickly catching up with it.

 

 

 

 

Buffalo Bayou Watershed Overview

(From http://www.hcfcd.org/L_buffalobayou.html)

 

Figure 2: Complete Buffalo Bayou Watershed (USGS), The Harris County Subwatersheds (HCFGD),

and The Buffalo Bayou Watershed (HCFGD)

 

About the Watershed


The Buffalo Bayou watershed is located in west-central Harris County and drains an area that is mostly within the City of Houston and, to a lesser degree, the Memorial Villages. Buffalo Bayou is the single primary stream within the watershed and also the sole outlet for the Addicks and Barker reservoirs. The bayou flows into the Houston Ship Channel after combining with White Oak Bayou and passing through downtown Houston. Buffalo Bayou becomes the Houston Ship Channel at the Turning Basin. The Buffalo Bayou watershed covers approximately 103 square miles and has about 47 miles of open streams within the watershed, including the primary stream and tributary channels. The estimated population within the watershed (Harris County portion) is just over 410,000.

Land Use
The watershed is almost entirely urbanized, except for the Clodine Ditch sub-area near Barker Reservoir, which is partially undeveloped.

Completed Plan Features
Early regional planning for the entire watershed was completed by the Corps. The Corps enlarged and straightened Buffalo Bayou from the Addicks and Barker dam outlets to approximately where Beltway 8 exists today.

Upstream of the I-610 West Loop, there are numerous tributaries flowing into Buffalo Bayou which have been included in various levels of subregional planning. Some are now concrete-lined channels, or have been fully enclosed as storm sewer systems; others have not been modified. Addicks and Barker Reservoirs were constructed to protect areas downstream along Buffalo Bayou and downtown Houston. Linear stormwater detention, to store excess flood waters, has been constructed by the District in the right-of-way of Buffalo Bayou between Wilcrest Drive and Dairy Ashford Road.

Environment
Buffalo Bayou passes through Terry Hershey Park, Memorial Park and Sam Houston Park. Although the watershed is highly urbanized, maintenance is generally limited to clearing debris blockages. Buffalo Bayou downstream of Beltway 8 is heavily wooded and in a natural state. Upstream of Beltway 8 to the reservoirs, Buffalo Bayou was cleared and enlarged in the 1950's, but has since regained natural characteristics.

 

Previous Studies

 

In 2005 George Rogers and Buren DeFee, from the College of Architecture at TAMU, took a detailed look at the effects of development on the White Oak Bayou watershed in Houston TX. White Oak Bayou watershed borders the Buffalo Bayou watershed to the north, eventually inputting into the Buffalo Bayou watershed just west of downtown Houston.

 

Urban growth in the White Oak Bayou watershed has for the most part mirrored that of the Buffalo Bayou watershed. Both areas have seen a huge influx of residential and commercial growth over the last 60 years and as a result a substantial increase in impervious cover. Both bayous only receive water input from rainfall and human activities. Both bayou systems travel west to east through primarily residential areas. Most importantly to this study, both bayou systems originally originated in sparsely populated undeveloped areas.

 

Using daily flow data from USGS stations situated along White Oak Bayou and daily precipitation data from the United States National Oceanic and Atmospheric Administration, Rogers and DeFee estimated a precipitation adjusted annual stream flow for White Oak Bayou. They then used annual development data from the Harris County Appraisal District (HCAD) combined with parcel level Land Use Land Cover maps to track land development over time.

 

 

Figure 3: Total developed area by type of development and year, White Oak Bayou

(Rogers, 2005)

 

The work of Rogers and DeFee clearly show an increase in total developed area over time. Working with the LULC maps and the data provided to them by the HCAD, Rogers and DeFee put together the growth statistics with the impervious cover data to create the following figure.

 

Figure 4: Impervious cover by type of property and year.

(Rogers, 2005)

 

Impervious cover has also been increasing. Impervious cover associated with commercial development increased from less than 1% of the total watershed in 1948 to 14.1% in 2000, while that associated with residential development grew from 0.5% in 1948 to 4.9% by 2000. Meanwhile, impervious cover associated with roads servicing the development in this area grew from 2.1% to 11.7%. This means the total impervious cover in the water shed grew from around 3% in 1948 to approximately 31% in 2000 a 10-fold increase.

 

Data Collection and Analysis

 

In order to quantify the hypothesis that urban growth results in increased surface water flow surface water data was needed for the area in question. All surface water discharge data came from the USGS Surface Water Dataset. Nationally, USGS surface-water data includes more than 850,000 station years of time-series data that describe stream levels, stream flow (discharge), reservoir and lake levels, surface-water quality, and rainfall. The data are collected by automatic recorders and manual measurements at field installations across the Nation.

This project used both Daily Value data and Annual statistical data. Daily values are summarized from time-series data for each day for the period of record and may represent the daily mean, median, maximum, minimum, and/or other derived value. Daily values include approved, quality-assured data that may be published, and more recent provisional data, whose accuracy has not been verified. Statistics are computed from approved daily mean time-series data at each site.

 

Data was collected for the following USGS Stations:

 

USGS 08073500 Buffalo Bayou near Addicks, TX

 

Latitude 29°45'42",   Longitude 95°36'20"   NAD27

Harris County, Texas   , Hydrologic Unit 12040104

 

Data Type

Begin Date

End Date

Annual Statistics

 

 

     Discharge, cubic feet per second

1945

2006

USGS 08073600 Buffalo Bayou at W Belt Dr, Houston, TX

 

Latitude 29°45'43",   Longitude 95°33'27"   NAD27

Harris County, Texas   , Hydrologic Unit 12040104

 

Data Type

Begin Date

End Date

Annual Statistics

 

 

     Discharge, cubic feet per second

1971

2006

USGS 08073700 Buffalo Bayou at Piney Point, TX

 

Latitude 29°44'48",   Longitude 95°31'24"   NAD27

Harris County, Texas   , Hydrologic Unit 12040104

 

Data Type

Begin Date

End Date

Annual Statistics

 

 

Discharge, cubic feet per second

1964

2006

 

USGS 08074000 Buffalo Bayou at Houston, TX

 

Latitude 29°45'36",   Longitude 95°24'30"   NAD27

Harris County, Texas   , Hydrologic Unit 12040104

 

Data Type

Begin Date

End Date

Count

Daily Statistics

 

 

 

     Discharge, cubic feet per second

1936-06-02

2006-08-11

14844

 

 

 

Precipitation data used came from the Texas Water Development Board (TWDB).  TWDB provides historical monthly evaporation and precipitation values via a web services applet.  The values available for the area in question span from 1940 to 2006.  TWDB uses a quadrangle method for reporting and accessing local data, dividing the State into individual quadrangle used to report back data.  The grid cells are one degree latitude by one degree longitude in size.  The data being reported back for each cell comes from several sources:  TWDB and National Weather Service Evaporation Stations, Hydrosphere National Climatic Data Center (NCDC), Summary of the Day Compact Disc, NCDC Climatologically Data Monthly or Annual for surrounding States:  Louisiana, Arkansas, Oklahoma and New Mexico, and additional internet data sources. 

 

USGS 08073500 Buffalo Bayou near Addicks, TX

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 5: Average annual discharge vs time for the Barkers Reservoir USGS gauging station.

 

Clearly evident from the Barkers Reservoir data set is an upward trend in surface water discharge with time. The Barkers Reservoir spillway remains open all the time and is only used to control water level in Buffalo Bayou during city festivals downtown and during times of heavy rainfall, to prevent flooding.

 

USGS 08073600 Buffalo Bayou at W Belt Dr, Houston, TX

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 6: Average annual discharge vs time for the West Belt (Beltway 8) USGS gauging station.

 

Clearly evident from the Barkers Reservoir data set is an upward trend in surface water discharge with time with a slope higher than the Barker Resevoir. This suggests that discharge levels in Buffalo Bayou are growing in time and not just in space.

 

USGS 08073700 Buffalo Bayou at Piney Point, TX

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 7: Average annual discharge vs time for the Piney Point USGS gauging station.

 

Clearly evident from the Barkers Reservoir data set is an upward trend in surface water discharge with time with a slope higher than the Barker Resevoir. This suggests that discharge levels in Buffalo Bayou are growing in time and not just in space.

 

USGS 08074000 Buffalo Bayou at Houston, TX

 

 

 

USGS Station

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 8: Average annual discharge vs time for the Memorial Park/Houston USGS gauging station.

 

 

In 1976 collection of Daily Discharge data ceased at the Memorial Park USGS Station. Data collection continues to this day, but at no particular interval. For this reason the annual discharge numbers available from USGS are not truly representative of actual flow conditions. Examination of daily discharge data from this time period reveals a vast range of actual flow rates ranging from 100s to many 1000s of cfs. For this reason there is no trendline included with the Average Discharge graph above.

 

 

 

Figure 9: Rainfall Volume vs Discharge

 

Figure 9 shows the volume of water falling over the total watershed area and the volume of water carried through Buffalo Bayou at each of the stations. This shows some very interesting trends. Because the water entering Buffalo Bayou at Barkers reservoir is not considered in the rainfall volume calculations (as the rain falls outside the Buffalo Bayou Watershed) it should be removed from both the graph and from the volume calculations.

 

 

Figure 10: Rainfall Volume vs Buffalo Bayou Load.

 

 

Figure 10 is a very basic water balance of the Buffalo Bayou Watershed, from the influent at Barker Reservoir to the USGS gauging station at Piney Point. Because the data available from the USGS gauging station at Memorial Park is spotty at best, it was removed from the calculation and the volume of the watershed was reduced to two thirds its original area. Subtracting the volume of water entering the watershed from the volume of water exiting gives us the net volume of water passing through the bayou system. This volume should be equal to the amount of water introduced to the system by rainfall less the amount of water evaporated and the volume of water recharging to groundwater.

 

Twice over the forty years shown the volume of water carried in the bayou during a one year span has exceeded the volume of water introduced by rainfall. There is a very clear upward trend in the volume of water carried by the bayou system.

 

 

Brief Conclusions

 

It has been clearly shown both in this term paper and in other more thoroughly researched reports that urban growth has a profound impact on the average daily discharge values of primary water bodies. An increase in impervious cover due to urban growth is most clearly to blame. Increases in impervious cover not only aid in the transport of rainwater but also decrease the amount of rainwater allowed to recharge shallow aquifers. In essence more water is diverted to surface water in a more efficient manor.

 

The hydrologic effects of urban development often are greatest in small stream basins where, prior to development, much of the precipitation falling on the basin would have become subsurface flow, recharging aquifers or discharging to the stream network further downstream. Moreover, urban development can completely transform the landscape in a small stream basin, unlike in larger river basins where areas with natural vegetation and soil are likely to be retained (Konrad, 2005). This is certainly true of the Houston metropolitan area, which prior to the introduction of major man-made surface water bodies, was nothing more than a piney wooded swamp. This effort to efficiently drain the land is not a thing of the past, but rather a machine still in motion, present today in the resurfacing of previously undeveloped lands.

 

The reduction of groundwater recharge has reeked havoc on the Houston metro area for 60+ years. Land subsidence and foundation failures are a way of life. If more water entered the groundwater system these problems would slow begin to remediate themselves.

 

Additionally, with less storage capacity for water in urban basins and more rapid runoff, urban streams rise more quickly during storms and have higher peak discharge rates than do rural streams (Konrad, 2005). This has never been more evident than during hurricane season. Repeated flood events over the last 60 years speak to this in dangerous and costly tones.

 

Urban growth cannot be stopped, but perhaps through insight into the ramifications of poorly planned expansion we can decrease the impacts of growth on the natural environment.

 

 

 

Acknowledgements

 

Mr. Clark Silar

 

Mr. Adam Czekanski

 

References

 

Konrad, C. P., 2005. Effects of Urban Development on Floods. USGS Fact Sheet 076-03

Rogers, G.O., DeFee, B.B., 2005. Long-term impact of development on a watershed: Early indicators of future problems. Landscape and Urban Planning. 73, 215–233

Pielke Sr. , R.A., Adegoke , J.,  Beltrán-Przekurat , A., Hiemstra , C.A., Lin, J., Nair , U.S., Niyogi , D., and Nobis, T.E., 2006. An Overview of Regional Land-Use and Land-Cover Impacts on Rainfall.

Auch, R., Taylor, J., Acevedo, W., 2004. Urban Growth in American Cities: Glimpses o U.S. Urbanization. USGS (http://pubs.usgs.gov/circ/2004/circ1252/)

Data Resources

 

·        Texas Water Development Board Evaporation and Precipitation Data:  http://hyper20.twdb.State.tx.us/Evaporation/evap.html

·        National Hydrologic Data Set:  http://nhd.usgs.gov/

·        Texas Natural Resource Information System:  www.tnris.State.tx.us/