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Technical Papers

Pecan Lakes Flood Protection System

Pecan Grove is a much-sought after residential community located in Richmond, Texas. In 2007, FEMA began remapping the area to update the flood insurance rate maps. Jones|Carter (JC), as the District Engineer and a participant in Fort Bend County’s technical review committee, evaluated the revised modeling and determined that after the remap, all 325 residents of Pecan Lakes Subdivision were now without flood protection, being located outside of the existing Pecan Grove Municipal Utility District Levee System. In 2008, JC evaluated the cost to provide flood protection to the affected subdivision that would be on par with the remainder of the Pecan Grove community. A bond election resulted in a record turnout with the measure passing by 69%. In 2009, JC began the design phase by evaluating multiple system alignments, each ranked based on benefit vs. cost. After receiving input from the client and residents, the selected design was a multi-component system consisting of an earthen levee, a structural floodwall, and a pump station. To read the entire article, please click here.

City of Houston Main Street Reconstruction

The partial removal of an existing railroad tunnel and subsequent raising of pavement on North Main allowed pavement on Burnett Street to be lowered, meeting the revised elevation of North Main Street. This feat allowed traffic to proceed through the revised alignment and mass transit to proceed to the METRO Park & Ride without taking a circuitous route via a u-turn, saving transit time and improving operational efficiency of METRO transit system.

Avoiding damage to and stabilizing the section of tunnel that would remain was a chief concern, as no record drawings existed to assist in formulating the construction phase. During construction, it was discovered the tunnel walls were made of stair-stepped massive non-reinforced concrete with a seven foot wide base narrowing to a thickness of two feet near the tunnel ceiling. The walls were topped with a three foot thick concrete slab reinforced with two foot I-beams separated by 12″. Conventional concrete saw-cutting and jackhammering methods were not an option for the demolition phase of the tunnel improvement project. Instead, a high speed diamond wire cable saw used for marble mining was employed to cut the tunnel structure. This method resulted in a clean tunnel cut with limited vibration. To read the entire article, please click here.

Cottage Grove Low Impact Development

The Cottage Grove Low Impact Development project, for the City of Houston (COH), has set the standard for urban redevelopment and the viability of incorporating Low Impact Development (LID) practices into future city projects. Jones|Carter (JC) evaluated various LID features related to roadway design in the redevelopment of Houston’s Cottage Grove subdivision as necessitated by polluted waters. We investigated solutions for utility conflict resolution, hydraulic evaluation of the drainage system to meet COH standards, evaluation of variances between LID and COH standards, and long and short term operation and maintenance of the proposed features. As a result of this work, JC helped COH complete its first LID roadway project constructed completely in the right-of-way. To read the entire article, please click here.

HCWCID 109 Surface Water Backfill Lines

North Harris County Regional Water Authority (Authority) was created June 18, 1999 when Texas House Bill 2965 was signed into law and voters confirmed the creation of the Authority. The Authority was created to ensure a secure and reliable supply of wholesale drinking water for all residents and entities within its boundaries, comprising of approximately 335 square miles and 460,000 residents. The primary goal of the Authority is compliance with the Harris-Galveston Subsidence District’s (HGSD) Regulatory Plan to prevent and cease the subsidence observed in the Harris County area by conservation of underground water sources. The Regulatory Plan requires a reduction in groundwater usage to no more than 20% of the total water demand by the year 2030. Should the Authority not meet the reduction goal of 20% groundwater usage by 2030, a monetary penalty of $5.00/1000-gallons will be imposed upon them by the HGSD. To ensure the Authority meets this reduction goal, all participating entities inside the District’s boundaries are aggregated into a single groundwater permit and participate in a single Groundwater Reduction Plan. The Authority delivers treated surface water from the Northeast Water Purification Plant (NEWPP) to all participating members of its GRP, but the remaining demand shall be supplemented by the use of groundwater. To read the entire article please click here.

To Repair or Replace

Water districts are faced with this decision frequently on the many pumps, blowers and drives that make up their water and wastewater systems. In the past, a rule of thumb was used to make this decision based on the cost of the repairs compared to the cost of a new replacement unit. The adage stated that if the repair was greater than 50% of the replacement cost, then it was better to replace the unit. The origin of this rule is unknown and the line of logic it follows questionable. The best guess is that for complicated equipment with many moving parts, a repair only brings a portion of the total machine back to manufacturer’s tolerances. If only half the machine were repaired, it might make sense that the other half may fail in short order and thus the total cost would be more than a new unit. To read the entire article, please click here.

Taste and Odor Issues Resulting from Chloramination and Nitrification

With a change to surface water many municipalities have had episodes of poor water quality that are the result of several factors. This memo is intended to give a little background on why conversion was necessary in the Houston area, a discussion of what those factors are, and recommendations on what to do as we move forward.

Our conversion to surface water in the Houston area is the result of subsidence, but many areas of Texas use surface water because of a lack of ground water. Surface water differs from ground water in many ways but of particular importance is that it has naturally occurring organic material in it. This is important because when disinfected with chlorine, this material forms byproducts that are shown to be carcinogenic. The byproducts are many and generally classified as either haloacetic acids or as trihalomethanes. Collectively they are called disinfection byproducts (DBPs) and are now regulated by the EPA. To avoid the formation of DBPs, many entities supplying surface water changed from using straight chlorine to chloramines, chlorine dioxide, or other disinfectants. Chloramines were the disinfectant of choice in Houston. Making chloramines is a tricky process, and the addition of too much chlorine can form Di- and Trichloramines that have a bad taste and odor. If chlorinated water were blended with chloraminated water the free chlorine residual would combine with the chloramines and form Di- and Trichloramines. This would be undesirable and thus the reason that all the regional water suppliers asked their customers to match their form of disinfection. To read the entire article, please click here.

Alum Control Alternative Assessment

In 1998 the Environmental Protection Agency (EPA) mandated that the country’s states impose limitations on nutrients entering its surface water resources. The primary nutrients targeted are nitrogen and phosphorus for their ability to severely impact the quality of the nation’s surface waters. In extreme quantities, these nutrients can cause eutrophication which is the rapid growth of algae, commonly referred to as algae blooms, and hypoxia or areas of rapid phytoplankton growth. Inland blooms are very unsightly, can kill aquatic life by reducing the dissolved oxygen concentrations and impart taste and odor problems for drinking water plants. In recent years hypoxia has received media attention as the limits of the “dead zone” in the Gulf of Mexico have been mapped. In accordance with the EPA’s mandate, the Texas Commission on Environmental Quality (TCEQ) began the laborious process of quantifying the problem through stream testing, identification of sources, a review of technological capabilities for nutrient removal and establishing a priority for nutrient reductions. The TCEQ’s State Implementation Plan calls for the reduction of nutrients and as such the TCEQ has begun writing discharge permits with technology based limits. To read the entire article, please click here.

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