Geology topics
Source-linked reports with geographic coverage including Nashville, Tennessee.
The aftermath, recovery, and lessons of the future following a major flood that inundated the greater Nashville area one year ago are the subjects of this article. The authors discuss what led up to the event, its impacts, and what, if anything, can be done to prevent or diminish the reoccurrence of such flooding in the future.
Rainfall, streamflow, and water-quality data were collected during storm conditions at five urban watersheds in Nashville, Tennessee. These data can be used to build a database for developing predictive models of the relations between stormwater quality and land use, storm characteristics, and seasonal variations. The primary land use and mix of land uses was different for each watershed. Stormwater samples were collected during three storms at each watershed and analyzed for selected volatile, acidic and base/neutral organic compounds; organic pesticides; trace metals; conventional pollutants; and several physical properties. Storm loads were computed for all constituents and properties with event mean concentration above the minimum reporting level. None of the samples contained acidic organic compounds at concentrations above the minimum reporting levels. Several constituents in each of the other categories, however, were present at concentrations above this level. For 21 of these, water-quality criteria have been promulgated by the State of Tennessee. For only 8 of the 21 did the value exceed the most restrictive of the criteria: pyrene, dieldrin, and mercury concentrations and counts of fecal * coliform exceeded the criteria for recreational use, copper and zinc concentrations and p value exceeded the criteria for fish and aquatic life, and lead concentrations exceeded for domestic supply.
Streamflow data from 14 basins in Davidson County were extended in time by use of a digital model of the hydrologic system. The basins ranged in size from 1.58 to 64.0 square miles (4.09 to 165.8 square kilometers) and ranged in extent of man-made impervious cover from 3 to 37 percent. The flood-frequency characteristics were defined by weighting frequency curves based on simulated discharges with those based on observed discharges. The average record length of the three rain-gages used in simulation was 72 years, and the average record length of observed discharges was 11 years. Discharges corresponding to 2-, 5-, l0-, 25-, 50-, and l00-year floods from the modeled basins were compared with discharges from regional equations for estimating peak discharge rates from rural basins. Lag times between rainfall and runoff in the urban basins were compared with those of nearby rural basins. The analyses indicated that in a fully-developed residential area, the flood peaks and the basin lag times will not be significantly different from those expected from an undeveloped area. Data were not sufficient to determine if an increase in flood peaks would occur from extremely small basins with extremely intensive development.