NHD Flow and Velocity Project Greg Schwarz, Reston, VA Alan Rea, Boise, ID
Needed: Estimates of flow and velocity for every reach in NHD • Useful for determining: • Dilution of pollutant loadings • Travel time between pollution sources and water intakes • Pollution attenuation with distance
Proposal • For every NHD reach, estimate - • Long-term mean annual flow and velocity • Long-term mean monthly flow and velocity • Long-term variance of annual and monthly flow and velocity • Derive 10th and 90th percentile flow estimates • 7Q10 flow • Measure of statistical accuracy for each estimate
Methodology • Statistical approach • Flow estimates best fit the available data • Provides a basis for estimating the accuracy of each estimate • Mass balance • Ensures that flow below a confluence equals the sum of the flows entering the confluence • Estimates of non-point pollution concentration derived by dividing non-point pollution load by flow are valid for arbitrarily small basins
Approach • Three pilot projects • Arkansas-White-Red River Basin flow pilot • Region of influence regression method • Flow is correlated with basin attributes across a group of basins having similar characteristics. • Large-scale RF1 flow pilot • Spatially Referenced Regression (SPARROW) model of flow applied to all RF1 streams • Simple process oriented model incorporating flow routing from the landscape to RF1 channels. • Flow accumulates according to the defined reach network.
Approach (continued) • Pilot to estimate velocity for every reach in RF1 • Regression method (Jobson, 1996) • Time of travel from dye studies • Relate to reach characteristics • flow • slope
The Pilots are Complementary • Arkansas-White-Red pilot provides an opportunity to gain experience with NHD and NED. • Large-scale RF1 pilots will investigate the diverse processes required to adequately model flow and velocity across the entire nation.
Arkansas-White-Red Pilot • Initially computing basin characteristics using EDNA • Will be used for first-run model development • Initial model calibration
Topographic Basin Characteristics • Basin area • Mean Basin elevation • Basin relief • Avg. basin slope • Percentage of area with slope >= 30% • Synthetic reach slope, node elevations
Thematic Basin Overlays • Mean annual precipitation (PRISM) • Mean annual temerature (PRISM) • Land cover percentages from NLCD, 9 general categories • Area-weighted average soil properties from STATSGO • Water use by 8-digit HUC • Percent area of playas / sand dune regions (AWR only)
Full Scale NHD Project • Apply what is learned from the pilots to develop regression-based flow and velocity models for the entire NHD network.
Data Needs • NHD reach locations for: • Approximately 4,000 gaging stations with 20 years of record since 1970 • 76,000 reservoirs from the National Inventory of Dams (NID) • 6,600 drinking water intakes • Not required for model estimation but included to provide functionality to the NHD project results.
Other Data Needs • Long term mean annual and monthly flow, and variance of annual and monthly flow for over 4,000 gaging stations with 20 years of record since 1970. • Data will be compiled from the NWIS data base. • Compile over 3,000 velocity measurements from USGS time of travel studies.
Other Data Needs • Basin boundaries for every NHD reach • Ongoing effort to derive basin boundaries for every NHD reach having an identified flow direction using the 30m NED. • Reach slope • Determine from NED.
Other Data Needs • Climate loadings • Precipitation and temperature estimates taken from the Prism climate model. • Flow diversions and consumptive use • Water use estimates by hydrologic unit apportioned to reaches on the basis of land use from the NLCD.
Final Products • Reach locations for gaging stations, reservoirs, and drinking water intakes. • Long-term mean annual and monthly flow and velocity estimates, with estimates of accuracy, for every reach in NHD. • Estimates of 10th and 90th percentile annual and monthly flows and velocities, and 7Q10 flow, with estimates of accuracy, for every reach in NHD. • Results will be made available via the internet. • Estimates will be revised periodically as data sets improve.