LWI Region 3 Modeling Overview

Rating Curve Development { Key steps were provided in 4.2.1 Boeuf Section. { Figure 4-13 displays an example of a best fit rating curve developed for the Kilbourne gage. { Figure 4-14 displays a comparison of rating curve predicted flow and the Hec-RAS model simulated flow at Kilbourne gage. LEARN MORE: (M_3.1.4) conducted using HEC-SSP for three USGS gages (Eudora, Kilbourne, Near Delhi) and one USACE gage (Como). { HEC-SSP discharge estimate for 1% AEP) supported the calibration of the 2D ROM HEC-RAS model. { Station skew was used instead of regional skew due to notable backwater effects at gage locations. { At Near Delhi, the station skew differed from regional skew by >0.5; per Bulletin 17C guidance, station skew was applied due to the long record length. { Frequency curves at all gages stayed within confidence limits and showed good agreement with plotted data. Figure 4-15 shows the Bulletin 17C plot for Eudora. LEARN MORE: (M_3.1.5) Model Result Analysis { Design storms (5- to 500-year, 24-hour) were simulated using Atlas 14 rainfall applying Areal ARF and fully saturated soil conditions. { Inflows at Eudora, derived from the Arkansas portion of HMS model, closely aligned with the HEC SSP 1% AEP flow estimate of 5,381 cfs. { RAS Model flows at Kilbourne, Near Delhi, and Como matched closely with their 1% AEPs. { HEC-RAS model results matched gage estimates well at Como and most locations across all AEPs. Greater deviations were noted at Near Delhi for higher-frequency events and at Kilbourne for lower frequency events. Table 4-1 compares the RAS and gage analysis flows. LEARN MORE: (M_3.2) b. Gage Analysis HEC-SSP { Bulletin 17C flood frequency analysis was

Figure 4-13: Best fit rating curve for the Kilbourne gage.

Figure 4-14: Comparison of rating curve predicted flow and original model flow at Kilbourne gage (Summer 2022).

Figure 4-15: Flow frequency plot for Eudora.

Table 4-1 Comparison of model peak and gage analysis flows, 100-year/24-hour storm. ( b Smoothed Peak)

MODEL FLOW (ARF), CFS

GAGE ANALYSIS FLOW (1% AEP), CFS

GAGE

5,455 3,350 b 7,207 4,842 b

5,381 3,692 7,140 5,030

Eudora (HMS flow)

Kilbourne Near Delhi

Como

47

Precipitation and Frequency Analysis and Consequence Modeling