Assessing Stormwater Management Infrastructure Within the City of Tampa

Funded by the City of Tampa

Overview

The City of Tampa and the Watershed Sustainability Lab have collaborated on stormwater projects across the city. Past work has focused on primarily on baffle boxes. Current work continues the previous work on baffle boxes and expands to other stormwater infrastructure, specifically wet detention ponds and the city’s green infrastructure projects. Below you will find the scope of work for past and current work.

Baffle Box Study Phase I

  1. Evaluated current conditions in the field for flow, basic water quality, and condition of each box. The Evaluation criteria was used to create community profiles of the general conditions for each baffle including neighborhood / community location; terrain; watershed; upstream BMPs such as ponds, exfiltration trenches, swales, and inlet traps; street conditions such as curbs and gutters, percent of tree canopy cover, receiving waters, and other catchment specifics. Additionally, the inclusion of size, model, and type of each baffle box will be noted as well as previously collected data on 47 baffle boxes. Interviews were conducted with field teams from the Transportation and Stormwater Services Department and Operations and Maintenance Division. The combined information was presented as a Baffle Box Database.

  2. Updated ArcGIS map and database for all baffle box locations and corresponding photos to be georeferenced.

  3. Updated assessment report to include recommendations for improvements of general effectiveness for each baffle box based on profile.

Baffle Box Study Phase II

  1. Quantification of sediment accumulation in baffle boxes: The city-wide investigation from Phase 1 was expanded to include estimates of sediment trapping and resuspension and the effect of watershed characteristics.

  2. Establishment of continuous monitoring: Four baffle boxes were instrumented with sensors to continuously measure sub-hourly information on water depth, electrical conductivity, and temperature, all of which are excellent indicators of stormwater runoff and could be used to accurately estimate continuous pollution loads into these stormwater units.

  3. Storm-based monitoring: Continuous monitoring was complemented with sampling during storm events, when water samples were collected at a fine frequency to detect the amount of suspended solids entering and leaving the unit.

Baffle Box Study Phase III

  1. Quantifying pollution loads into stormwater units: It is critical to understand the overall loading from each units’ contributing catchment in order to understand to overall performance and effectiveness of stormwater BMPs through the city. This was carried out with a numerical model that integrates information on rainfall, drainage and land use. During this new phase, the initial model will be configured, and it will continue to be calibrated and improved with data collected in the field.

  2. Continuation of monitoring: In April of 2018, sample number of units were selected for monitoring and instrumented with sensors to continuously measure sub-hourly information on water depth, electrical conductivity and temperature, all of which are excellent indicators of stormwater runoff and could be used to accurately estimate continuously pollution loads into these stormwater units. The units were monitored in cooperation with the City of Tampa project management team for one additional year.

  3. Storm-based monitoring: Continuous monitoring was complemented with sampling during storm events, when water samples will be collected at a fine frequency to detect the amount of suspended sediments entering and leaving the unit. A total of 20 storm events were observed during Phases II and III.

  4. Recommendations provided for the Lake Roberta existing model for upgrades and/or replacement of a newer model for maximum efficiency.

  5. Identification of rain gauges in the City of Tampa and creation of an ArcGIS layer for utilization of existing gauge data locations for all of the baffle boxes in the COT inventory and placement of rain gauges on the monitoring sites for rainfall data as deemed necessary if current stations are not sufficient for analysis was completed.

City of Tampa Stormwater BMP Inventory & Efficiency Study

  1. Development of a model for baffle box performance: Using data from ongoing monitoring storm-based monitoring as well as clean-up schedules, a statistical model to understand the relative contribution from different drivers of performance of baffle boxes. Some of the drivers to be tested will include unit volume, cumulative rainfall since last event, rainfall intensity, watershed characteristics, etc.  Overall, this model will be used to provide product selection (treatment features & size), installation and operation recommendations that enhance the sediment removal efficiency of baffle boxes.

  2. Recommendations for baffle box optimal cleaning schedule: based on the model developed in Task 1, a set of recommendations for clean-up timing and frequency will be provided for each of the operational baffle boxes in the City.

  3. Inventory of conditions of existing stormwater ponds and other BMPs in WBID1443E: There are 242 City of Tampa owned stormwater ponds. The Transportation and Stormwater Services Department currently maintains 137 in their inventory (77 dry & 60 wet). We will perform verifications on current conditions in the field and water quality performance. Similar to how it was carried out for baffle boxes in 2017, this task will document the current conditions of existing  ponds and grassy lots in the City of Tampa, with particular emphasis to those in the Lower Hillsborough River watershed (WBID 1443E).

  4. Establishment of monitoring of water quantity and water quality performance of stormwater ponds: Based on the condition inventory from Task 3, this Task will provide recommendations for specific ponds where to establish hydrologic and water quality monitoring to accurately determine pollutant removal efficiencies.