Calculating Hydrologic Parameters for Estimating Surface Water Flow at Ungaged Locations Richard Hoffpauir Water Resources Engineering

Gaged Locations

Ungaged Locations

Estimating Flow at Ungaged Locations Proportional change in drainage area and average upstream parameters

Linear Relationship Assumed Gaged Ungaged

Other Methods for Estimating Flow at Ungaged Locations Modifying an emperical model calibrated to a gaged location (e.g. SCS Curve Number Method) Regionalized precipitation-runoff regression Hydrologic simulation (e.g. HEC-HMS)

Why is this important? Surface water withdrawl permits are not always granted next to stream gaging stations. Flow at the permitted location is used to determine the user’s withdrawl reliability. Further complicating the scenario, the permitted volume of withdrawl affects the flow and reliability for downstream users.

1997 Texas Senate Bill 1 Comprehenisive regional water resources planning for future demands and droughts Water Availability Modeling (WAM) Water Rights Analysis Package (WRAP)

Application of WRAP Flow at ungaged locations is typically modeled using parameter ratios. Priority based water allocation model Existing water management policies can be evaluated with historical stream flow data. Proposed water withdrawl permits are evaluated based on their impact to downstream users.

WRAP Parameters ArcView Script Brad Hudgens CRWR Online Report 99-4 Interface to simplify calculation of upstream parameters for a set of control points on a stream network

Objectives of My Project Develop GIS datasets for the Brazos River Basin (e.g. flow accumulation, stream network, control points, CN, precip, etc) and to become proficient with the WRAP Parameters ArcView tools. Compare hydrologic parameters obtained at 67 control points to the values submitted to the TNRCC as part of the WAM project for the Brazos.

Datasets Used for this Project Grid: USGS 1-Degree DEM (1:250,000 accuracy) Grid: U.S. Curve Number Grid: U.S. Mean Annual Precipitation Lines: EPA RF3 and NHD Channel Lines (1:100,000 accuracy) Points: Control Point Locations

Brazos River Basin Los Brazos de Dios 46,000 sq. miles 36,000 sq. miles contributing 16% of surface area of Texas 25 Hydrologic Unit Codes (HUC’s)

WRAP Parameters Method Stream Channels Corrected Channels Burned DEM Flow Area Accumulation Stream Network DEM Filled DEM CN and Avg. Rain Area, CN, Rain Accumulation Control Points Flow Distribution Parameters original datasets

Correcting RF3 Channel Lines Replacing open water boundaries with channel centerlines Deleting braided channels Removing or connecting broken channels Erasing interior dangling nodes

Replacing Open Water Body Boundaries

Deleting Braided Channels

Flow Area Accumulation Grid

Stream Network

Why Build a Stream Network? Control point locations may match exactly to channel grid cells in the flow accumulation grid. Snapping control points to the stream network lines ensures the control points will define the correct outlet locations on the flow accumulation grid. Downstream control points can be identified on the stream network and incremental subwatershed changes in hydrologic parameters can be computed.

67 Control Points

WRAP Parameters Method Stream Channels Corrected Channels Burned DEM Flow Area Accumulation Stream Network DEM Filled DEM CN and Avg. Rain Current Status Area, CN, Rain Accumulation Control Points Flow Distribution Parameters original datasets