Table 1 summarises the low flow measurements of the four gauging stations which matter for the prevention of zero flow at the Park Headquarter.

According to the “Sustainable Management of the Usangu Wetland and its Catchment, Final Report (ref. 28 page 32) Most of the larger rivers in the east and south of the project area have reliable curves, the several smaller catchments in the south west had poor quality curves.”

This conclusion may be valid for the larger flows which have not been assessed on their quality. It is clear from Table 1 above that the quality of the low flow measurements and the resulting rating curves which are important for understanding the occurrence of zero flow in the National Park, are inadequate for hydrological modeling.

Complete Low Flow Data Series Ruaha from Inflow Usangu to Flow at Park.

For proper simulation and modeling of the Usangu Subbasin complete low water flow series over several years of the Ruaha River network will include the inflow to the plain, the outflow from the plain and ultimately the flow at the Park HQ which is the focus of the (zero) flow monitoring. (Inflow to plain – drainage from Rice Irrigation Area – Natural Losses on the plain and en route through the park = drainage to Ruaha River in the Park).

Apart from already mentioned lack of reliable rating curves of the four stations (see Table 1), completeness of non-manipulated³⁷ low flow data for the four stations including the minimum (zero flow) values are also an issue ((Map 1) Complete low flow series of non-manipulated data of the four stations are available for the years 2001, 2006, 2007 and 2008 (Database Min. of Water). The inflow data for Mbarali and Ruaha and related low flow data at the Park HQ for the dry season flows in Hydrological Year Book of the Ministry only include 2012, 2014, and 2017 series. For these three years no drainage data for the Usangu Rice Plain have been found. The screenshot of the Year Book indicates the highlighted “suspicious” data series for the period 2010 to 2019. It is noted that the Year Book flow data deviate slightly from the database flows, possibly a better correlating mathemetical relation between the stages and flow is used than the rating curve specified in Ministry’s spreadsheet flow data.