Part One in a Three-Part Series on HARC’s program of work and research utilizing LiDAR in the Houston-Galveston region.
From Data to Images
Have you noticed posted warnings about contaminated water at your local creek, bayou or beach?
After heavy rains, it is not uncommon for our local waterways and beaches to experience impaired water quality. State agencies monitor water quality to ensure it is not a threat to humans and aquatic life. Bacteria can cause health concerns for humans and excessive nutrients like nitrogen and phosphorus can be problematic for aquatic life because of resulting low levels of oxygen in water (fish and other aquatic animals need to breathe too). Sources of this type of water contamination include faulty sewage treatment, pet and animal waste, and fertilizers. Runoff from land to a stream after rainfall can carry with it pollutants washed from the surrounding landscape – these pollutants then make their way into our bayous and eventually Galveston Bay. Some waterways only experience water quality issues after major rainstorms, while for others, poor water quality is an ongoing issue.
Runoff water is not usually treated, but nature has its own way of dealing with excess nutrients and bacteria. Wetlands are natural filters that trap and hold water, pollutants and debris, allowing material to settle out of the water and keeping contaminants out of our waterways. Wetlands also help contain floodwaters, retaining water to slow down flow as well as allow the water to seep into our groundwater, filtering it along the way. Retention basins that hold water in a cement-lined bayou or basin, or even those with grass, do very little to improve water quality. It takes slow moving water and lots of exposure to wetland plants, soils and microbes to filter water effectively. Natural wetlands are by far the best filters because they have the right soil, the right microbes and the right vegetation all in balance. However, restored wetlands can also play a role in improving water quality and slowing the release of flood waters to area waterways.
Wetlands can take many forms. They can be forested or have shrub or grass-like vegetation. While saltwater wetlands fringe coastal bays, freshwater wetlands can be found many miles inland. Some look like prairies until rainwater fills their pothole-like depressions. Many wetlands in our region appear dry when it hasn’t rained in a while, but this doesn’t mean that they aren’t still a wetland. A combination of the right type of soil and the right type of vegetation is what defines a wetland. Wetland soils and plants have evolved to tolerate long periods of drought and flood – a pattern that now seems the norm for Texas. For example, the buttonbush shrub (Cephalanthus occidentalis), one of a wide variety of wetland plants, takes up huge amounts of water and nutrients in flood waters – keeping those nutrients from flowing downstream.
Flooding…What can we do?
One of the most obvious problems in the Houston region lately is the volume of flood water that can result from a single rain event. A Houston Chronicle article1 estimated that 240 billion gallons of rain fell across the Houston region on April 18, 2016 – enough water to fill 750 Astrodomes. How do we even begin to manage that volume of water?
Standard engineering approaches to dealing with flood water are no longer sufficient on their own in our growing region. As we assess the damage left behind by the most recent of many flood events in our region, we should look downstream as well as upstream for causes and solutions. It is time that we recognize that the development patterns of the past will not solve our development needs in the future. As our regional population continues to increase, and we develop in outlying areas upstream of existing neighborhoods and communities, we need to connect the dots and recognize wetlands for the valuable role that they play in capturing rainfall, mitigating floods, and improving water quality. Wetland conservation is a water strategy and should be a regional priority.
A New Source of Information
The Galveston Bay Report Card (www.GalvBayGrade.org) grades watersheds based on wetland loss, water quality, and bacteria. The watersheds with the lowest wetland grades also have the lowest grades for bacteria.
Of the 21 bayous that were assessed for remaining freshwater wetlands that hold runoff and developed lands that speed up the release of rainfall runoff, three regional watersheds scored an “F”: Brays Bayou, White Oak Bayou and Buffalo Bayou. These were followed by seven bayou watersheds that scored D’s, five C’s and six B’s. There are no bayou watersheds in the Houston region with the grade of an “A”.
|Austin-Bastrop Bayou||B||Barker Reservoir||C|
|East Fork San Jacinto||B|
|Houston Ship Channel||D|
|San Jacinto River||C|
|West Fork San Jacinto||B|
|White Oak Bayou||F|
What makes a wetland?
If you’d like to know if the creek, bayou or beach close to where you live is suffering from impaired water quality or if you are curious whether there has been a lot of wetland loss in your watershed, visit the Galveston Bay Report Card (www.GalvBayGrade.org). As with any report card, grades are a snapshot in time; they can improve or they can worsen. What will we as a region choose to do and how will we implement positive change? One thing is for certain, it will require a regional will to change current practices and the leadership to make it happen.