CRWR-PrePro Calculation of Hydrologic Parameters Francisco Olivera, Ph.D. Center for Research in Water Resources University of Texas at Austin

Hydrologic Parameters Watershed Abstractions and routing method Parameters Stream Routing method

Watershed Abstractions and Routing Method Abstractions: rainfall/runoff transformation SCS curve number method Initial loss + constant rate loss Routing: runoff/flow transformation Soil Conservation Service (SCS) synthetic unit hydrograph

Watershed Abstractions Precipitation (mm/hr) Runoff (mm/hr) Soil properties Runoff = f(precipitation, land use, soil properties, moisture conditions, temperature, wind)

Watershed Routing Runoff (mm/hr) Watershed Flow (m3/s)

Watershed Routing Time Runoff (mm/hr) Runoff and Flow Flow (m3/s) Time Flow = f(runoff, watershed hydrologic properties)

Hydrologic Parameters Watershed Abstractions and routing method Parameters Stream Routing method

Watershed Abstractions Average Curve Number Initial Loss (mm) Constant Loss (mm/hr) SCS Method Initial + Constant Method

Watershed Routing SCS Unit Hydrograph Area (Km2) Area (Km2) Average Curve Number Length of longest flow path (m) Slope of longest flow path (m/m) Lag time Area (Km2) Length of longest flow path (m) Average flow velocity (m/s) Lag time SCS Unit Hydrograph

Hydrologic Parameters Sub-basin lag-time according to the SCS formula: tp: sub-basin lag-time (min) LW: length of sub-basin longest flow-path (ft) CN: average Curve Number in sub-basin S: slope of the sub-basin longest flow-path (%) t: analysis time step (min)

Watershed Lag-Time (SCS) Flow length upstream and downstream Average Curve Number Identification of the longest flow-path Length and slope of the longest flow-path Lag-time

Hydrologic Parameters Sub-basin lag-time according to 0.6 L/v formula: tp: sub-basin lag-time (min) Lw: length of sub-basin longest flow-path (ft) Vw: average velocity sub-basin longest flow-path (m/s) t: analysis time step (min)

Watershed Lag-Time (L/V) Flow length upstream and downstream Longest flow-path average velocity Identification of the longest flow-path Length of the longest flow-path Lag-time

Elevation Grid

Flow Length Downstream

Flow Length Upstream

Longest Flow-Path

Flow Length Downstream to the Watershed Outlet

Hydrologic Parameters Flow length downstream to the sub-basin outlet.

Flow Length Upstream to the Watershed Divide

Hydrologic Parameters Flow length upstream to the sub-basin divide. A NODATA cell is defined at the sub-basin outlets before running the flow length function.

Watershed Longest Flow-Path

Hydrologic Parameters Sub-basin longest flow-path. The longest flow-path is the geometric locus of the points for which the sum of both flow lengths is a maximum.

Slope of Watershed Longest Flow Path

Hydrologic Parameters Sub-basin parameters: Grid code, area (Km2), unit hydrograph model (SCS), length of longest flow path (m), slope of longest flow path (m/m), average curve number, lag-time (min), baseflow (none).

Hydrologic Parameters Watershed Abstractions and routing method Parameters Stream Routing method

Routing Method

Pure-Lag Method tlag: flow time in the reach I: inflow to the reach Q: outflow from the reach Flow is delayed a fixed amount of time tlag.

Muskingum Method S: storage in the reach K: flow time in the reach (Dt < K < Dt/2X) X: storage parameter I: inflow to the reach Q: outflow from the reach Dt: analysis time step Flow is delayed a fixed amount of time K, and redistributed around its centroid.

Routing Method Flow time (Ls/Vs) Ls/Vs < Dt Ls/Vs > Dt Pure Lag Routing Muskingum Routing Ls: length of the stream Vs: flow velocity in the stream Dt: analysis time step

Hydrologic Parameters Watershed Abstractions and routing method Parameters Stream Routing method

Hydrologic Parameters Reach lag-time for Pure Lag routing: tlag: reach lag-time (min) Ls: length of reach (m) Vs: reach average velocity (m/s)

Hydrologic Parameters Reach lag-time and number of sub-reaches for Muskingum routing: K: Muskingum parameter K (hr) X: Muskingum parameter X Ls: reach length (m) Vs: reach average velocity (m/s) n: number of sub-reaches

Hydrologic Parameters Reach parameters: Grid code, sub-basin code, length(m), velocity (m/s), routing method (Lag or Muskingum), Muskingum X, Muskingum K (hr), number of sub-reaches, lag time (min).