APPCOR12259 - Laserfiche WebLink

Home Browse Search

Ltr/Revw Bsln Env Data - 5 - July 2, 1986 3. Comparison of the mean concentrations of the 1973-1981 Bureau of Reclamation data to that collected in the 1984 program at the same location (5-5) should be completed to establish a single set of baseline conditions for Big Salt Wash. iii. Flood Flow Monitoring. The information derived from the monitoring program on peac~fTow determinations is lacking. Crest-stage recorders were observed on a monthly basis. Flows were estimated using Manning's equation. It is uncertain what velocities and "n" values were used in deriving the estimates. The estimates provided in Table 2.04.7-7A are questionable based on internal inconsistencies in the data. Two events are estimated for the period between June 14 and August 3, 1984. This is possible if the larger event occurred first but it is listed second. A review of precipitation data in Table 2.04.7-5A shows no appreciable rainfall during this period. However, a significant event (1.60 inches) fell prior to June 14 for which no flood flow is estimated. Based on these inconsistencies, the characterization of peak flow in the basins is unresolved. The original application listed two empirical methods for determining peak flows after which the monitoring program was defined to collect site-specific data. A clear definition of a single peak flow value for each station should be defined and provided in the application. The Division suggests additional monitoring at the sites be performed to resolve this information requirement. (B). Dry Gulch. The response to the additional information requeste o~n~y Gulch has not been fully addressed. A discussion of the "Probable Hydrologic Consequences" was omitted in the original application and the response given in Vol. I-A is unsubstantiated. The water quality data available from the monitoring in 1984 at the Dry Gulch station is not discussed in the response. All streamflow is attributed to intense storm events although the flow sampled was preceded by moderate rainfall amounts. The statement that no snow accumulates during winter does not indicate whether the snowmelt runs off, infiltrates, or evaporates due to a lack of monitoring during this period. The statement that runoff does not contribute to streamflow but rather recharges the alluvium is not consistent with the October 2, 1984 monitoring and can not be substantiated based on the limited data available from the monitoring program. A peak flow estimate also needs to be provided for the Dry Gulch basin.