Christie M. O’Day | Geology Reports

USGS2001

Statistical summary of selected physical, chemical, and toxicity characteristics and estimates of annual constituent loads in urban stormwater, Maricopa County, Arizona

Stormwater and streamflow in Maricopa County were monitored to (1) describe the physical, chemical, and toxicity characteristics of stormwater from areas having different land uses, (2) describe the physical, chemical, and toxicity characteristics of streamflow from areas that receive urban stormwater, and (3) estimate constituent loads in stormwater. Urban stormwater and streamflow had similar ranges in most constituent concentrations. The mean concentration of dissolved solids in urban stormwater was lower than in streamflow from the Salt River and Indian Bend Wash. Urban stormwater, however, had a greater chemical oxygen demand and higher concentrations of most nutrients. Mean seasonal loads and mean annual loads of 11 constituents and volumes of runoff were estimated for municipalities in the metropolitan Phoenix area, Arizona, by adjusting regional regression equations of loads. This adjustment procedure uses the original regional regression equation and additional explanatory variables that were not included in the original equation. The adjusted equations had standard errors that ranged from 161 to 196 percent. The large standard errors of the prediction result from the large variability of the constituent concentration data used in the regression analysis. Adjustment procedures produced unsatisfactory results for nine of the regressions?suspended solids, dissolved solids, total phosphorus, dissolved phosphorus, total recoverable cadmium, total recoverable copper, total recoverable lead, total recoverable zinc, and storm runoff. These equations had no consistent direction of bias and no other additional explanatory variables correlated with the observed loads. A stepwise-multiple regression or a three-variable regression (total storm rainfall, drainage area, and impervious area) and local data were used to develop local regression equations for these nine constituents. These equations had standard errors from 15 to 183 percent.

Arizona↗

USGS2001

Quality of water and estimates of water inflow, northern boundary area, Fort McDowell Indian Reservation, Maricopa County, Arizona

Increased agricultural and recreational activities and recent growth of population centers within the Verde River basin have led to concerns about the quality and quantity of water flowing onto the Fort McDowell Indian Reservation. The purpose of this study was to determine the quality and quantity of water in the Verde River and in the shallow stream-channel deposits in the vicinity of the northern boundary of the reservation. The quality of surface water entering the reservation at the northern boundary and of ground water in the shallow stream- channel deposits beneath the flood plain is suitable for most purposes. Concentrations of dissolved solids and major ions did not exceed water-quality standards. Dissolved oxygen and pH generally were in acceptable ranges for all designated uses. Total coliform counts and nutrient concentrations also did not exceed water-quality standards. Six organic compounds were detected; however, concentrations of these compounds were below U.S. Environmental Protection Agency Maximum Contaminant Levels. The presence of these organic compounds indicates that the water has been affected by anthropogenic activities. Concentrations of all trace metals were below the applicable State of Arizona Water Quality Standards for Surface Water and U.S. Environmental Protection Agency Maximum Contaminant Levels. Arsenic concentrations were below the Maximum Contaminant Level of 50 micrograms per liter at the time of collection and analysis; however, in January 2001, the U.S. Environmental Protection Agency set a new Maximum Contaminant Level of 10 micrograms per liter. All arsenic concentrations in surface water were 10 micrograms per liter or greater. Arsenic concentra-tion in ground water ranged from 6 to 9 micrograms per liter. The source of arsenic is probably oxidized arsenic compounds that are typically found in basin-fill sediments in southern Arizona. Surface-water flow onto the reservation was determined from recorded discharge at the Verde River below Bartlett Dam and Verde River near Scottsdale streamflow-gaging stations from 1962?99. Average annual flow onto the reservation is about 13 cubic feet per second less than average annual discharge at the Verde River below Bartlett Dam and 17.5 cubic feet per second more than the average annual discharge at the Verde River near Scottsdale for years in which rainfall is less than 20 inches. Average daily flow onto the reservation also is about 13 cubic feet per second less than discharge at the Verde River below Bartlett Dam and 18.7 cubic feet per second more than discharge at the Verde River near Scottsdale for May through November. Flow onto the reservation for December through April is less predictable because of a large variation between dis-charges at the Verde River below Bartlett Dam and the Verde River near Scottsdale. Correlation between the nine instantaneous discharge measurements made between January 1998 and August 1999 at the northern boundary and recorded discharge at the two streamflow-gaging stations is high; correlation coefficients were greater than 0.99. Instantaneous inflows onto the reservation can be related to discharges at the Verde River below Bartlett Dam and the Verde River near Scottsdale using the equations: instantaneous inflow = 0.861(instantaneous discharge at the Verde River below Bartlett Dam) + 20 cubic feet per second, and, instantaneous inflow = 0.893(instantaneous discharge at the Verde River near Scottsdale) + 36 cubic feet per second for discharges that range from 102 to 704 cubic feet per second at the northern boundary. The direction of ground-water flow is approximately parallel to the flow of the Verde River. Ground water has a minor component of flow into the river when the river stage is lower than about 5 feet above the local datum. There is a minor component of flow into the stream-channel deposits when the river stage is higher than about 5 feet above the local datum. Ground-water inflow to the reservation in the Verde River streamchannel deposits is about 1.1 cubic feet per second and is minor compared to the average annual streamflow of 675 cubic feet per second at the Verde River below Bartlett Dam on the basis of 111 years of record.

Arizona↗

USGS2000

Computed roughness coefficients for Skunk Creek above Interstate 17, Maricopa County, Arizona

In the winter of 1997-98, the U.S. Geological Survey, in cooperation with the Flood Control District of Maricopa County, made six verification measurements for Manning's roughness coefficients at Skunk Creek above Interstate 17. Data from four floodflows were recorded and analyzed, three of these flows occurred in February 1998 when Arizona received precipitation from the El Nino weather phenomenon. Discharges ranged from 187 to 760 cubic feet per second and resultant verified values for Manning's roughness coefficient, n, ranged from 0.056 to 0.039. Skunk Creek above Interstate 17 - an ephemeral wash within a flood-control structure - is overgrown with desert brush throughout the main channel and the presence of the vegetation has a significant effect on n values throughout the reach. The results of this study are verified roughness coefficients that can be transferred to similarly vegetated channels in Maricopa County and other arid and semiarid environments where roughness factors must be assessed for flood management or other purposes.

Arizona↗