and 28-Day streamflow. For a more comprehensive description of raster hydrographs, see Strandhagen et al. (2006). Lag-1 hydrograph A Lag-1 hydrograph is a graph of discharge which can be accomplished without a time axis (Koehler 2022). This technique allows data properties such as Q, dQ/dt, and d2Q/dt2, and trends of increasing, decreasing or no change flow to be readily seen and understood on a single graph. Flow pulse reference lines can easily be added and interpreted. The methodology is based on the time-series serial correlation lag-1 graph and uses the normally unwanted (but still valuable) autocorrelation present within the streamflow data. The x-axis represents the discharge for a date, Qt, while the y-axis represents the discharge for the next day, Qt+1. Data preparation and plotting methods are identical to an autocorrelation lag 1 plot, where 1 indicates a 1-day or daily time step. The table below shows how the time-series discharge are shifted. It is critical that the temporal sequence is maintained for the data. Thinking of the x values as “flow for today” and the y values as “flow for tomorrow” helps visualize the order of the data. See also Aquifer test Hydrogeology Baseflow Routing (hydrology) Runoff model (reservoir) Stream gauge Surface water References Keim, D.A. 2000. Designing pixel-oriented visualization techniques: theory and applications. IEEE Transactions on Visualization and Computer Graphics, 6(1), 59-78. Koehler, R. 2004. Raster Based Analysis and Visualization of Hydrologic Time Series. Ph.D. dissertation, University of Arizona. Tucson, AZ, 189 p. Koehler, R. 2022. In preparation, The Lag-1 Hydrograph – An Alternate Way to Plot Streamflow Time-Series Data. American Institute of Hydrology Bulletin, Winter 2022. Strandhagen, E., Marcus, W.A., and Meacham, J.E. 2006. Views of the rivers: representing streamflow of the greater Yellowstone ecosystem (hotlink to http://geography.uoregon.edu/amarcus/Publications/Strandhagen-et-al_2006_Cart_Pers.pdf). Cartographic Perspectives, no. 55, Fall. L. Sherman, "Stream Flow from Rainfall by the Unit Graph Method," Engineering News Record, No. 108, 1932, pp. 501-505. External links The U.S. Geological Survey (USGS) offers real-time streamflow data for thousands of streams in the United States. The U.S. Geological Survey (USGS) also offers an online toolkit to create a raster hydrograph for any of its streamflow gaging stations in the United States. SCS Dimensionless Unit Hydrograph. SERC activity and Matlab code for calculating and using Unit Hydrograph. Hydrology Hydraulic engineering