BASIN DISCRIPTION

Buzi, Pungwe and Save Basins

The Buzi, Pungwe and Save (BUPUSA) Basins have a total area of 161 446 sq km shared by Mozambique (MOZ) and Zimbabwe (ZWE) (Table 1, Figure 1). The largest parts of the Pungwe and Buzi, 95.3% and 87.1% respectively, occur in Mozambique with the remainder being in Zimbabwe. In contrast, the Save Basin has 83% of the area in Zimbabwe and covers 21.5% of this country. The Save Basin covers 9% of the national area of Mozambique. The total area of the three basins is almost shared equally by the two countries with 44.7% being in Mozambique and 55.3% in Zimbabwe (Table 1).

Table 1: Basin areas of the BUPUSA Basins, and the proportions of the basin areas falling in Mozambique and Zimbabwe repectively.

	Pungwe	Buzi	Save	Total – BUPUSA
Basin Area (km²)	31 151	28 870	101 425	161 446
Area of Basin in MOZ (km²)	29 690	25 137	17 277	72 104
Area of Basin in ZWE (km²)	1 461	3 733	84 149	89 343
% of the Basin in MOZ	95.3	87.1	17.0	44.7
% of Basin in ZWE	4.7	12.9	83.0	55.3
% of MOZ National Area	3.7	3.1	2.2	9.0
% of ZWE National Area	0.4	1.0	21.5	22.9

The three basins have watersheds or catchment divides with relatively high altitude, 800 – 2500 m above sea level, occurring along the Mozambique – Zimbabwe border (Figure 1). These high altitude areas comprise the Vumba (peak height 1911 m), Chimanimani (2430 m) and Nyanga Mountains (2592 m) which have a north-south orientation stretching for about 300 km. The Save Basin has on the western and northern part a 1400 – 1700 m high watershed with the Zambezi River. The Save Basin also shares a watershed with the Limpopo River on the southern part. The areas with relatively high altitude, greater than 1400 m, have significant effects on climate such as having a) relatively low average annual temperatures than would be expected in a tropical location, and b) high rainfall due to the orographic effects. Although these areas have limited spatial extent, they contribute significantly to river flows in each basin.

Figure 1: BUPUSA River Basins which are exclusively shared by Mozambique and Zimbabwe

Surface Water Resources

The Save Basin has been subdivided into 12 sub-basins (9 in Zimbabwe, 3 in Mozambique) for water resources assessment and management at the transboundary level (Figure 5). The Pungwe Basin has 12 sub-basins (2 Zimbabwe, 10 Mozambique), while these are 11 for the Buzi Basin (3 Zimbabwe, 8 Mozambique).

Figure 5: Sub-basins of the Save, Pungwe and Buzi Basins used for water resources assessment and management.

Information contained in the Water Sharing agreements and reports of previous investigations was used to determine the available water resources;

Figure 6: Mean annual runoff with most parts of the Save Basin generating less than 100 mm/year, and 200 – 1200 mm/yr for the mountainous border regions..

The Mean Annual Runoff (MAR) ranges from 80 mm/yr (8157 Mm³/yr) for the Save Basin, 143 mm/yr (4450 Mm³/yr) for the Pungwe Basin, and 197 mm/yr (5701 Mm3/yr) for the Buzi Basin.(Table 1, 2, 3) (Hydroconsult, 2017; Consultec, 2013, 2015). The most productive regions in terms of runoff production are the mountainous areas with altitudes above 800 m and occurring mainly along the Mozambique-Zimbabwe border (Figure 1, 2 and 5). Due to the significant topographic gradient dominating the mountainous areas, the proportion of rainfall forming runoff or runoff coefficient varies from 30% to 60%. Globally, mountain areas like the ones in the BUPUSA Basins that produce significant amounts of surface flows and sustain base flows during dry season are considered as strategic water source areas or water towers.

Buzi Basin

About 60% of the Buzi Basin has relatively high runoff with MAR ranging from 200 to 380 mm/yr (Table 2). As expected the mountainous areas are the most productive with MAR of 260 – 380 mm/year. The Lucite Zimbabwe sub-basin covers 5% of the Buzi Basin and generates 10% of the 5701 Mm³/yr basin flow (Table 1) (Consultec, 2015).

Table 1: Mean annual runoff of the sub-basins of the Buzi Basin

Sub-basin	Basin Area (km²)	% of Basin Area	MAR (Mm³/yr)	MAR (mm/yr)	% of Basin Runoff
Revue Zimbabwe	510	1.8	173	339	3.0
Lucite Zimbabwe	1 540	5.3	582	378	10.2
Buzi Zimbabwe	1 690	5.9	446	264	7.8
Sub-total ZWE	3 740	13	1 201	321	21.0

Upper Buzi	4 480	15.5	898	200	15.8
Middle Buzi	4 330	15	411	95	7.2
Lower Buzi	3 260	11.3	189	58	3.3
Upper Lucite	3 250	11.3	1124	345	19.7
Lower Lucite	1 880	6.5	267	141	4.7
Upper Revue	2 330	8.1	499	213	8.8
Middle Revue	2 460	8.5	451	182	7.9
Lower Revue	3 140	10.9	661	210	11.6
Sub-total MOZ	25 130	87	4 500	179	79.0

Total	28 870	100	5701	197	100.0

The runoff coefficient for the basin is as high as 27% in the mountainous upper parts of the basin and 18% for the whole basin.

Pungwe Basin

Table 1 gives an area of the Honde Sub-basin in Zimbabwe as 776 km² which differs from that given in the Pungwe Water Sharing Agreement. The agreement gives this area as 1245 km² which is incorrect as this includes the part of the Honde Basin within Mozambique up to the Pungwe River confluence. The Pungwe Monograph in Annex I Sector Study on the Surface Water Resources of the Pungwe River Basin states on Page 13 that 1463 km² of the whole Pungwe Basin is in Zimbabwe (SWECO, 2004). This is made up of 687 km² of the Pungwe Zimbabwe, 528 km² Honde River up to the border, and 248 km² of the Nyamkwarara River. The combined area of the Nyamkwarara River and Honde River up to the border is 776 km² referred to in this report as Honde Zimbabwe. Thus Honde Mozambique covers 469 km². Table 1 provides the mean annual runoff (MAR) of all the sub-basins of the Pungwe Basin.

The Pungwe Basin in Zimbabwe covers about 5% of the whole basin. This has an MAR ranging from 426 – 1124 mm/yr, and contributes 25% of the average annual flow of the whole basin (Table 1 and Figure 6) (Consultec, 2013). The Nyazonia Sub-basin of the Pungwe Basin is also highly productive and has an MAR of 325 mm/yr. The Urema and Lower Pungwe Sub-basins have altitude in the 10 – 200 m, low gradient and hence have relatively low runoff, 82 and 71 mm/yr respectively.

Table 2: Mean annual runoff of sub-basins within the Pungwe Basin (Consultec, 2013)

Sub-Basin	Area (km²)	% Basin Area	MAR (Mm³/yr)	MAR (mm/yr)	% Basin MAR
Pungwe Zimbabwe	687	2.2	772	1 124	17.3
Honde Zimbabwe	776	2.5	330	426	7.4
SUB-TOTAL ZWE	1 463	4.7	1 102	753	24.8

Honde Mozambique	469	1.5	200	426	4.5
Upper Pungwe	2 846	9.1	328	115	7.4
Nyazonia	1 360	4.4	442	325	9.9
Middle Pungwe	5 390	17.3	574	107	12.9
Vunduzi	3 439	11.0	499	145	11.2
Muda	1 336	4.3	160	120	3.6
Lower Pungwe	6 445	20.7	458	71	10.3
Urema	8 402	27.0	687	82	15.4
SUB-TOTAL MOZ	29 687	95.3	3 348	113	75.2

TOTAL	31 150	100	4 450	143	100

The proportion of mean annual rainfall (MAP) that constitute mean annual runoff or runoff coefficient is 60% on the mountainous part in Zimbabwe, 5% – 6% in the lowlands, i.e. Urema and Lower Pungwe sub-basins, and 11% for the whole basin.

Save Basin

The MAR of the Save Basin is 8157 Mm³/yr or 80 mm/yr (Hydroconsult, 2017). The Mozambican part of the basin contributes 16% while this is 84% for Zimbabwe. The southern and eastern parts of the Save Basin are semi-arid receiving 500 – 700 mm/yr of rainfall. These regions generate in comparison to all other BUPUSA sub-basins relatively low runoff, 30 – 70 mm/yr (Table 3, Figure 6). The Upper Save and Odzi sub-basins are the most productive with MAR of 115 mm/yr and 159 mm/yr respectively.

Table 3: Mean annual runoff for sub-basins of the Save Basin.

Sub-Basin	Area (km²)	% of Basin Area	MAR (Mm³/yr)	MAR (mm/yr)	% of MAR
Upper Runde	15 802	15.6	900	57	11.0
Lower Runde	5 802	5.7	179	31	2.2
Tokwe	7 947	7.8	543	68	6.7
Mutirikwe	7 941	7.8	477	60	5.8
Chiredzi	3564	3.5	166	46	2.0
Devure-Nyazwidzi	8 153	8.0	768	94	9.4
Upper Save	17 791	17.5	2 041	115	25.0
Odzi	7 239	7.1	1 154	159	14.2
Lower Save	9 910	9.8	595	60	7.3
Sub-total ZWE	84 149	83.0	6 822	81	83.6

Massagena	4 510	4.4	198	44	2.4
Conare	6 501	6.4	523	81	6.4
Save-Estuary	6 266	6.2	613	98	7.5
Sub-total MOZ	17 277	17.0	1 335	77	16.4

Total	101 426	183.0	8 157	80	100.0

The Save Basin has a low runoff coefficient of 11% with this being 15% – 16% in the Odzi and Upper Save sub-basins, and 6% in the low lying Lower Save and Massangena sub-basin.

2. Climate in the Basins

The average annual rainfall is 1050 mm/yr for the Pungwe Basin, 1085 mm/yr for Buzi Basin, and 715 mm/yr for the Save Basin. Within the Pungwe Basin average annual rainfall ranges from 900 mm/yr in the Urema Sub-basin located on the lower eastern part to 2000 mm/yr over the Nyanga Mountains in Zimbabwe (Figure 2). The Buzi Basin has a similar spatial pattern of rainfall with the Lower Buzi Sub-basin receiving 900 mm/yr and the Upper Lucite Sub-basin which drains the Chimanimani Mountains having an average rainfall of 1300 mm/yr. There is considerable spatial variability of rainfall over the Save Basin. Rainfall increases from about 550 mm/yr on south-western parts to 900 mm/yr on the northern parts, and to 1200 mm/yr over the Odzi Sub-Basin on the north-eastern part of the Save Basin (Figure 2).

All the three basins have high interannual variability of rainfall irrespective of whether a location receives low or high rainfall (Figure 3). In some years, the annual rainfall received can be as low as 50% to 60% of the long-term average annual rainfall or as high as 120% to 150%. The BUPUSA basins are frequently affected by tropical storms and cyclones which have significant effects on rainfall received and river flows including flooding. On average the Pungwe and Buzi Basins are affected by a tropical storm every year, and a cyclone once in three years, all which originate from the South-West Indian Ocean. During some of the severe cyclones such as Eline in 2000 and Idai in 2019 up to 200 – 400 mm of rainfall can be received within 1 to 2 days resulting in severe flooding and landslides in mountainous areas. Cyclone Idai caused deaths of over 700 persons, displaced 400,000 persons, and affected over 1.5 million in Mozambique and Zimbabwe.

Figure 2: Spatial variation of average annual rainfall within the Save, Buzi and Pungwe Basins

Figure 3: Annual rainfall expressed as a percentage of mean annual average rainfall for Chipinge (1086 mm/yr) and Masvingo (633 mm/yr)

The relatively humid and cool to warm conditions in most parts of the Pungwe and Buzi Basins lead to low pan evaporation rates, 1000 – 1400 mm/yr (Figure 4). The Save Basin in contrast has a warm and dry climate, hence pan evaporation are generally in the 1800 – 2000 mm/yr range. These high evapotranspiration rates substantially affect the availability of water resources particularly in surface water bodies. Most dams will lose about 10% to 20% a year of the water stored due to evaporation and reduces the reliable water yield. The design of storage capacities of dams in the BUPUSA has to be increased to overcome the adverse effects of evaporation.

Figure 4: Relatively low evaporation rates within the Pungwe and Buzi Basins, while high rates occur in the Save Basin.

3. Groundwater resources

Most parts of the BUPUSA basins have basement complex rocks such as granites and gniesses (Figure 7). These rocks are primarily impermeable. Groundwater occurs whether is weathering to significant depths, and/or the occurrence of fissures and fractures that impart secondary permeability. Aquifers in these formations are generally of local importance supporting for village water supply. Most boreholes have depths of 30 – 60 m and yield 1 litre/sec.

Unconsolidated sedimentary rocks occur on the lower parts of the three basins (Figure 7). Aquifers in these formations have high productivity, greater than 10 litres/sec. The most significant groundwater resource occurs within the unconsolidated sedimentary Save alluvium in Zimbabwe which covers about 1350 km² along the Save River (Figure 7). This aquifer and water released from the upstream Osborne Dam on the Odzi River support irrigation of about 15 000 hectares including at Nyanyadzi, Middle Save, Chibuwe and Chisumbanje. The Save alluvial aquifer is not transboundary in terms of spatial extent. However, groundwater abstraction from this aquifer can induce recharge from the Save River flows which can have transboundary effects. During the dry season, most of the flows of the Save River along the stretch with the alluvial aquifer are due to water releases from Osborne Dam. Hence the transboundary implications of groundwater abstractions are not clear cut. There has also been a suggestion that water abstracted from boreholes for irrigation is in some cases surface water which will have recharged the alluvial aquifer. A potential exists for double counting the same water, i.e. surface water from the Osborne Dam is then counted as groundwater after recharging the alluvial aquifer.

Figure 7: The productivity of aquifers within the BUPUSA Basin. (L) = low productivity 0.01 – 1 litre/sec, (M) = moderate productivity 1 – 10 litres/sec, (H) = high productivity > 10 litres/sec.

VisionRI (2020) estimated groundwater recharges rates and then assumed that 10% of this can be sustainably utilized in the Save Basin in Zimbabwe. On this basis the available groundwater resource for the Save Basin in Zimbabwe was estimated to be 780 Mm³/yr (Runde Catchment 250 Mm³/yr; Save Catchment in Zimbabwe 530 Mm³/yr). SWECO (2011) used the same approach but assumed that 55% of groundwater recharge can be utilized in Buzi Basin. The available groundwater in the whole Buzi Basin was estimated to be 1257 Mm³/yr. Using the same approach, the available groundwater resources in the Pungwe Basin is estimated to be 1628 Mm³/yr.

4. Current Water Uses as of 2023

Buzi Basin

The total amount of water currently used (2020) in the Buzi Basin is 339 Mm³/yr. Irrigation accounts for 81% of the water demand. Water supply to the following urban centres Chipinge and Chimanimani (Zimbabwe), Chimoio, Manica and Gondola (Mozambique) is the second largest water user (Figure 9) (Consultec, 2015). During previous studies on water use in the Buzi Basin, the amounts of water consumed by plantation forests were not included because the effects were assumed to be reflected in the estimated MAR. Since these plantations were established a long time ago, the effects on river flows are reflected in the MAR. While not included in Table 5, plantation forests are estimated to utilise 45 Mm³/yr and 30 Mm³/yr in Zimbabwe and Mozambique respectively.

Table 5: Estimated current (2020) water demand (Mm³/yr) by the various sectors in the Buzi Basin

Sub-basin	Rural	Urban	Livestock	Irrigation	Industrial	Total	% of Basin Total
Revue Zimbabwe	0.32	–	0.29	61.00	2.40	64.01	19.1
Lucite Zimbabwe	1.75	0.64	0.38	89.00	1.50	93.27	27.9
Buzi Zimbabwe	2.44	2.35	1.31	103.00	2.00	111.10	33.2
Sub-total ZWE	4.51	2.99	1.98	253.00	5.90	268.38	80.3

Upper Revue	0.96	28.40	0.36	2.00	0.50	32.22	9.6
Middle Revue	0.67	–	0.34	2.00	0.30	3.31	1.0
Lower Revue	0.67	–	0.41	3.00	0.40	4.48	1.3
Upper Lucite	0.54	–	0.47	1.00	0.20	2.21	0.7
Lower Lucite	0.54	–	0.23	1.00	0.10	1.87	0.6
Upper Buzi	0.93	–	0.63	1.00	0.20	2.76	0.8
Middle Buzi	0.72	–	0.47	–	0.30	1.49	0.4
Lower Buzi	0.72	–	0.25	14.00	2.70	17.67	5.3
Sub-total MOZ	5.73	28.40	3.16	24.00	4.70	65.99	19.7

TOTAL	10.24	31.39	5.14	277.00	10.60	334.37	100.0

The urban sector in Zimbabwe is the largest water user (43%) followed by crop irrigation (Figure 9)

Figure 9: Contribution of the various sectors to water demand in Buzi Basin

Pungwe Basin

The estimated total water use in 2020 in the Pungwe Basin is 808 Mm³/yr (Table 4) with crop irrigation accounting for 67% of this amount, followed by the urban sector, 25% (Figure 8) (Consultec, 2013) . Irrigation of sugar cane plantations in the Lower Pungwe Sub-basin, e.g. Mafambisses, use most of the water taken by the irrigation sector. The City of Mutare in Zimbabwe meets part of the water requirements from the Pungwe Basin. This is done by diverting 0.7 m³/s upstream of the Pungwe Falls into a 4 km tunnel and then a 46 km pipeline to this city. Beira and Dondo are the major urban settlements depending on the Pungwe Basin for water supply. Several major rural settlements like Hauna in Zimbabwe, Catandica and Gorongosa in Mozambique are significant users of water.

Table 4: Current water uses (Mm³/yr) by various sectors in the Pungwe Basin

	Urban	Rural Water	Irrigation	Livestock & Tourism	Industry	Total	% of Total
Pungwe Zimbabwe	112		66			177	22
Honde Zimbabwe		11	42			53	7
Sub-total ZWE	112	11	107	–	–	230	28

Upper Pungwe			5			5	1
Nyazonia			75			75	9
Middle Pungwe		9	44	5	32	90	11
Muda			34			34	4
Lowe Pungwe	92		276		7	375	46
Sub-total MOZ	92	9	434	5	39	579	72

TOTAL	203	20	541	5	39	808	100

Water used for rural water supply and livestock watering amount to 3% of the total water use in the Pungwe Basin (Figure 8).

Figure 8: Contribution to water use by the various sectors in the Pugwe Basin.

Save Basin

The estimated current water use in the Save Basin is 7844 Mm³/yr and Zimbabwe accounts for 98% of this amount (Table 6). Crop irrigation is the largest consumer of water amounting to 91% of the total water use at the basin level (Figure 10). In Mozambique water for crop irrigation accounts for 61% of the Save water used in this country. Water uses in the Runde Sub-basin in Zimbabwe which has very large dams such as Tokwe-Mukosi (1802 Mm³), Mutirikwi (1378 Mm³) account for about 70% of the total water used in the Save Basin.

Figure 10: Contribution of the sectors to water use in the Save Basin

Table 6: Estimated amounts (Mm³/yr) of water used by the various sectors in the major sub-basins of the Save Basin.

Sub-basin	Irrigation	Urban	Rural	Mining	Livestock	Others	Total	% of Basin Total
Save Zim	1 838	14	81	5	210	25	2 174	28
Runde	5 190	63	54	16	153	4	5 480	70
Sub-total ZWE	7 029	77	134	21	363	29	7 653	98

Massangena	43	4	3	40	1	3	93	1
Covanne & Estuary	94		3		1		97	1
Sub-total MOZ	137	4	5	40	2	3	191	2

Basin Total	7 165	81	140	61	365	32	7 844	100

WATER QUALITY

Buzi

There are few systematic data on water quality in surface and underground watercourses in BuPuSa. Perhaps more comprehensive and more exhaustive studies of water quality in the Buzi Basin are from Steinbruch (2016) and Consultec (2015), referring to surveys on the physical-chemical and microbiological characteristics of surface water in the dry season, carried out during November 2016. These studies aimed at establishing the baseline for monitoring water quality, identifying possible regions with water quality problems at the sub-basin level, identifying possible anomalies in the composition of surface water and identifying strategic locations for the water quality monitoring.

Measured parameters included salts, pesticide contents, microbial load, metals, nutrients, turbidity, pH, Electrical Conductivity (EC) and dissolved oxygen (DO) at designated locations along the Buzi basin (Figure 5). Table 2 presents the results for pH, Turbidity, Total Coliforms, Ammonia, Nitrates and Phosphorus in Buzi catchment. The turbidity results indicated that the waters near the sources, e.g. near the Chimanimani, Station 25, and inside the Chicamba reservoir, Station 24, recorded low values (2.72-5.59 NTU), owing to pristine forest cover in the Chimanimani National Park, which consolidates soils for erosion and filters sediments, hence cleaner water, while waters coming from Zimbabwe to Chicamba, Station 26, had high turbidity values (80.21-879 NTU), probably due to intensive mining in the river bed coupled with poor forest cover in Zimbabwean side. The coliform level was relatively low, with the maximum in the high Revue, high Lucite and high Buzi zone being 101-240 CFU/100 ml. Water from Chicamba, Station 26, was more neutral, with pH 7.6-8.5, while water from Zimbabwe, Station 29, had a more acidic pH, with values 7.1-7.5. The Nitrate load was high in the water coming from the CNP and in the Chicamba reservoir (8-9 mg/L). Note that the whole scale of pH ranges from 0-14, with 7 being neutral. pH values less than 7 indicate acidity, while pH values greater than 7 indicate basicity. The natural turbidity of the waters is, generally, between 3 and 500 NTU; for potability purposes, it should be less than 1 NTU. The limit values for ammonia in drinking water are 0.25-32.5 mg/L. The safe level of nitrate in drinking water is 10 mg/L. Natural phosphate levels generally range from 0.005 to 0.05 mg/L.

Figure 5: Places where the measurement of water quality indicator parameters was carried out in Buizi river catchment (source: Steinbruch, 2016).

Table 2: pH, turbidity, microbial and nutrients in water courses in Buzi river catchment (Steinbruch, 2016).

Sub-basin	Station	Local	pH	Total coliforms [UFC/100 ml]	Turbidity [NTU]	NH₄ [mg/L]	N0₃ [mg/L]	P [mg/L]
High Revue	19		7.6-8.5	1-100	2.72-5.59		7
	20		7.6-8.5	1-100	2.72-5.59		7
	21		7.1-7.5	1-100	47.61-80.20		7
	22		7.1-7.5	101-240	47.61-80.20		8
	23		7.1-7.5	1-100	2.72-5.59		8
	24	Chicamba reservoir	7.6-8.5	1-100	2.72-5.59		9
	25	Entrance of the Chicamba reservoir from Zimbabwe	7.1-7.5	101-240	2.72-5.59		2
	26	Entrance of the Chicamba reservoir from Chimanimani Park	7.6-8.5	101-240	80.21-879		8
High Lucite	13		6.5-7.0	101-240	47.61-80.20
	14		6.5-7.0	1-100	2.72-5.59
	15		6.5-7.0	101-240	47.61-80.20
	16		6.5-7.0	101-240	47.61-80.20
High Buzi	29		7.6-8.5	1-100	2.72-5.59	1.1	8	0.1

Table 3 presents the concentration of some heavy metals in Buzi river catchment, according to surveys carried out by Steinbruch (2016). Relatively high concentrations of heavy metals, Ni (0.80 mg/L), Cu (0.30 mg/L), Zn (0.10 mg/L), Pb (0.008 mg/L) and Titanium (0.002 mg/L) L), were recorded in the tributaries that feed the Chicamba Reservoir, coming from the Chimanimani national park and its buffer zone, while the concentration of heavy metals from tributaries that enter the Reservoir from Zimbabwe is relatively low.

Table 3: Concentration of heavy metals in water courses in Buzi catchment (Steinbruch, 2016). Values highlighted in red exceed WHO limits.

Sub-basin	Station	Local	Ni [mg/L]	Cu [mg/L]	Zn [mg/L]	Pb [mg/L]	Titanium [mg/L]
High Revue	19					0.001	0.008
	20			0.002			0.004
	21		0.009	0.002			0.007
	22			0.002			0.020
	23			0.002			0.003
	24	Chicamba reservior		0.002			0.002
	25	Entrance to the Chicamba reservoir from Zimbabwe	0.009	0.003			0.009
	26	Entrance to the Chicamba reservior from Chimanimani park	0.080	0.030	0.1	0.008	0.002
High Lucite	13			0.002		0.001	0.01
	14			0.003		0.003	0.02
	15			0.002			0.01
	16		0.003	0.004	0.004		0.007
High Buzi	29			0.003			0.002

According to Global Water Partnership news, released in 19^th August 2022 (GWP, 2022) the Zimbabwean side of the Buzi basin was heavily exploited for agriculture and related activities, while the mid and lower reaches of the basin in Mozambique was not as intensively utilised compared to the Zimbabwean side. On the other hand, recent studies conducted by BIOFUND (BIOFUND 2022) have indicated that in the upper Buzi, the ecosystems and hence the water quality is pristine, due to the fact that there is a National Park, The Chimanimani National Park in which the ecosystems are preserved. Climate Resilience Infrastructure Development Facility report (CRIDF, 2015) indicated that the Buzi River was moderately polluted with fertilisers, pesticides and herbicides, used on both small- and large-scale farms in the Basin. However, artisanal gold mining activity was identified as the major source of pollution for both the surface and groundwater courses (GWP, 2022). There are several small-scale mining projects in the Buzi catchment, especially in Upper Revue, where gold and greenstones (such as Cu, Fe, Al) are mined in the river beds (Consultec, 2015). Other activities with adverse effects on water quality identified included were inadequate cultivation in slope ground and deforestation, which were said to have led to soil exposure to erosion, land degradation, and consequent increased sediment loads in surface water courses (GWP, 2022).

Thus, the major water quality issues in the Buzi basin are nutrient enrichment from agricultural activities, pollution from gold mining activities (especially artisanal gold panning) and changes in sediment load, due to inadequate land use and management (Consultec, 2015).

Pungwe

The water quality in the upper reaches of the Pungwe River in Zimbabwe is almost pristine because there is national park, the Nyanga National Parks where human settlements are forbidden by law (GoM, 2006). For the rest of the catchment, water quality is influenced by human settlements, agriculture, afforestation, gold panning and salt water intrusion. Although the latter is a natural phenomenon, it can be exacerbated by high abstraction of water from the river during the low flow season.

Despite the water quality in Pungwe is considered reasonably good (Consultec, 2013), there were records of high levels of pollutant contaminants, though within acceptable ranges, and these were turbidity in Nyamukwara and Nyamukombe catchments, high iron content in Nyamhingura, Ruda and Honde and high zinc content in Ruda and Nyamhingura. There were records of high content TSS, COD and BOD in whole the extension of Pungwe basin (Conusltec, 2013).

In all these, the alluvial gold mining in the Nyamukwarara, Nyamukombe and Nyamhingura rivers are the most significant source of pollution (GoM, 2006). Figure 6 shows the location of the main gold mining. The inadequate cultivation practices in sloping ground and deforestation are other source of pollution to be considered, as they exposure the soil to erosion, and thereon causing increased sediment load and siltation in the river and lakes.

Figure 6: Location of gold mines in Pungwe river (Source: GoM, 2006)

Save

The water quality in Save and its tributaries is mostly affected by: inadequate sanitation in the main cities and villages (ZWF, 2014), industrial effluents and alluvial mining. The resulting contaminants enters the natural river water courses as point and diffuse sources. Point sources are mainly from urban and industrial drainage (ZWF, 2014)) and artisanal mining, whereas the diffuse sources are largely from agricultural runoff and artisanal mining. Siltation, due to excessive sediment load, bought by soil exposures due to deforestation is also one of the sources of pollution reported in the natural water courses in save catchment, where the western drier lands show large amounts of siltation and the astern highlands have cleaner water because of high runoff available and because of the protection provided by the national parks that are there.

Water quality in the Save catchment is reasonably monitored on the Zimbabwean side, with 20 parameters being measured compared to the Mozambican side, where only at one station, near the Bridge in Vila Franco do Save, at lower Save is monitored. Studies conducted in the Zimbabwe side of the basin, in Odzi (Table 4) and Runde (Table 5) rivers, as measured in Abril-May 2013, at stations indicated in Figure 7, where values highlighted in red exceed WHO limits. In Runde, the concentration of iron exceed the World Health Organization (WHO) standards in all stations. (Hydroconsult, 2017) have indicated high values of Alkanity, COD, Iron, Manganese, Phosphate and TSS.

Artisanal mining activity remain the main source of pollution in save catchment, according to Murwira at al. (2014) and Lupankwa et al. (2006), whose studies recorded high concentrations of (Fe), nickel (Ni), copper (Cu), cobalt (Co), lead (Pb), zinc (Zn), and sulphate ions (SO4^2-).

Table 4. Chemical parameters of surface water sampled in Save and in Runde catchments, a tributary of save in Zimbabwe, measured in Abril-May 2013. Values highlighted in red exceed WHO limits.

Parameter	Range
BOD	<2-36.8 mg/L
COD	<1-109 mg/L
DO	66.6-226.9 µg/L
Cl	11-58.2 %₀
Cu	0.01-0.02 mg/L
NO₃	0.55-1.46 mg/L
TSS	2-462 mg/L
Fe	0.02-3.37 mg/L
Cu	0.01-0.02 mg/L
Mn	0.01-0.28 mg/L
Ni	<0.01 mg/L
Zn	<0.01-0.02 mg/L

In Mozambique side, water quality monitoring was conducted in single station, at Vila Franco de Save, at lower save (Hydroconsult, 2017). Nitrates (NO³) and nitrites (NO²) were less than 10 mg/L and about 0.07 mg/L, respectively; Chlorides varied in the range 2.8-205.6 mg/L; Alkalinity varied in the range 26-172 mg/L; and Faecal coliforms varied in the range <3 to 460 ufc/100 mL (Hydroconsult, 2017). Total Suspended Solids (TSS) was above the accepted level, which may be attributed to poor land use practices, which causes erosion and artisanal mining. Unfortunately, in Mozambique side there is monitoring of heavy metals.

Table 5: Chemical parameters of surface water sampled in Save and in Runde catchments, a tributary of save in Zimbabwe, measured in Abril-May 2013. Values highlighted in red exceed WHO limits.

Catchment	Station	Chloride [mg/L]	Sulphate [mg/L]	Nitrate [mg/L]	Ammonia [mg/L]	Fe [ppm]	Ni [ppm]
Save	CHIPIN	21.3	11.8	0.204	0.012	0.68	N/D
Save	DTZ 1	7.1	112.8	0.003	0.014	0.53	N/D
Save	EL 2	21.3	144.2	0.032	0.027	1.39	N/D
Save	EPR 106	7.1	74.5	0.041	0.025	1.50	N/D
Save	ER 13	14.2	48.3	0.007	0.015	1.67	N/D
Save	ER 13 A	35.5	30.3	0.003	0.106	2.30	N/D
Save	ER 49 A	7.1	19.9	0.005	0.014	0.94	N/D
Save	ER 56 A	7.1	12.6	0.034	0.015	0.37	N/D
Save	ER 86 A	63.8	49.2	0.165	0.103	0.99	N/D
Runde	EL 7A	7.1	23.4	0.024	0.011	0.10	N/D
Runde	ER 118C	7.1	24.2	0.007	0.014	0.11	N/D
Runde	ER 1A	70.9	15.2	0.054	0.010	0.45	N/D
Runde	ER 30A	14.2	0.0	0.009	0.010	0.55	N/D
Runde	ER 3A	21.3	16.9	0.007	0.011	N/D	N/D

N/D: stands for not detected. Values in red had exceed the WHO standards (source: Murwira et al. (2014)).

Figure 7: Location of the water quality determination stations in the catchment in Zimbabwe. Attention is drown to Save and in Runde catchments (a tributary of Save Siver) (Murwira et al., 2014).

BASIN DISCRIPTION

Table 1: Basin areas of the BUPUSA Basins, and the proportions of the basin areas falling in Mozambique and Zimbabwe repectively.

	Pungwe	Buzi	Save	Total – BUPUSA
Basin Area (km²)	31 151	28 870	101 425	161 446
Area of Basin in MOZ (km²)	29 690	25 137	17 277	72 104
Area of Basin in ZWE (km²)	1 461	3 733	84 149	89 343
% of the Basin in MOZ	95.3	87.1	17.0	44.7
% of Basin in ZWE	4.7	12.9	83.0	55.3
% of MOZ National Area	3.7	3.1	2.2	9.0
% of ZWE National Area	0.4	1.0	21.5	22.9

Figure 1: BUPUSA River Basins which are exclusively shared by Mozambique and Zimbabwe

Surface Water Resources

Figure 5: Sub-basins of the Save, Pungwe and Buzi Basins used for water resources assessment and management.

Information contained in the Water Sharing agreements and reports of previous investigations was used to determine the available water resources;

Figure 6: Mean annual runoff with most parts of the Save Basin generating less than 100 mm/year, and 200 – 1200 mm/yr for the mountainous border regions..

Buzi Basin

Table 1: Mean annual runoff of the sub-basins of the Buzi Basin

Sub-basin	Basin Area (km²)	% of Basin Area	MAR (Mm³/yr)	MAR (mm/yr)	% of Basin Runoff
Revue Zimbabwe	510	1.8	173	339	3.0
Lucite Zimbabwe	1 540	5.3	582	378	10.2
Buzi Zimbabwe	1 690	5.9	446	264	7.8
Sub-total ZWE	3 740	13	1 201	321	21.0

Upper Buzi	4 480	15.5	898	200	15.8
Middle Buzi	4 330	15	411	95	7.2
Lower Buzi	3 260	11.3	189	58	3.3
Upper Lucite	3 250	11.3	1124	345	19.7
Lower Lucite	1 880	6.5	267	141	4.7
Upper Revue	2 330	8.1	499	213	8.8
Middle Revue	2 460	8.5	451	182	7.9
Lower Revue	3 140	10.9	661	210	11.6
Sub-total MOZ	25 130	87	4 500	179	79.0

Total	28 870	100	5701	197	100.0

The runoff coefficient for the basin is as high as 27% in the mountainous upper parts of the basin and 18% for the whole basin.

Pungwe Basin

Table 2: Mean annual runoff of sub-basins within the Pungwe Basin (Consultec, 2013)

Sub-Basin	Area (km²)	% Basin Area	MAR (Mm³/yr)	MAR (mm/yr)	% Basin MAR
Pungwe Zimbabwe	687	2.2	772	1 124	17.3
Honde Zimbabwe	776	2.5	330	426	7.4
SUB-TOTAL ZWE	1 463	4.7	1 102	753	24.8

Honde Mozambique	469	1.5	200	426	4.5
Upper Pungwe	2 846	9.1	328	115	7.4
Nyazonia	1 360	4.4	442	325	9.9
Middle Pungwe	5 390	17.3	574	107	12.9
Vunduzi	3 439	11.0	499	145	11.2
Muda	1 336	4.3	160	120	3.6
Lower Pungwe	6 445	20.7	458	71	10.3
Urema	8 402	27.0	687	82	15.4
SUB-TOTAL MOZ	29 687	95.3	3 348	113	75.2

TOTAL	31 150	100	4 450	143	100

Save Basin

Table 3: Mean annual runoff for sub-basins of the Save Basin.

Sub-Basin	Area (km²)	% of Basin Area	MAR (Mm³/yr)	MAR (mm/yr)	% of MAR
Upper Runde	15 802	15.6	900	57	11.0
Lower Runde	5 802	5.7	179	31	2.2
Tokwe	7 947	7.8	543	68	6.7
Mutirikwe	7 941	7.8	477	60	5.8
Chiredzi	3564	3.5	166	46	2.0
Devure-Nyazwidzi	8 153	8.0	768	94	9.4
Upper Save	17 791	17.5	2 041	115	25.0
Odzi	7 239	7.1	1 154	159	14.2
Lower Save	9 910	9.8	595	60	7.3
Sub-total ZWE	84 149	83.0	6 822	81	83.6

Massagena	4 510	4.4	198	44	2.4
Conare	6 501	6.4	523	81	6.4
Save-Estuary	6 266	6.2	613	98	7.5
Sub-total MOZ	17 277	17.0	1 335	77	16.4

Total	101 426	183.0	8 157	80	100.0

The Save Basin has a low runoff coefficient of 11% with this being 15% – 16% in the Odzi and Upper Save sub-basins, and 6% in the low lying Lower Save and Massangena sub-basin.

2. Climate in the Basins

Figure 2: Spatial variation of average annual rainfall within the Save, Buzi and Pungwe Basins

Figure 3: Annual rainfall expressed as a percentage of mean annual average rainfall for Chipinge (1086 mm/yr) and Masvingo (633 mm/yr)

Figure 4: Relatively low evaporation rates within the Pungwe and Buzi Basins, while high rates occur in the Save Basin.

3. Groundwater resources

Figure 7: The productivity of aquifers within the BUPUSA Basin. (L) = low productivity 0.01 – 1 litre/sec, (M) = moderate productivity 1 – 10 litres/sec, (H) = high productivity > 10 litres/sec.

4. Current Water Uses as of 2023

Buzi Basin

Table 5: Estimated current (2020) water demand (Mm³/yr) by the various sectors in the Buzi Basin

Sub-basin	Rural	Urban	Livestock	Irrigation	Industrial	Total	% of Basin Total
Revue Zimbabwe	0.32	–	0.29	61.00	2.40	64.01	19.1
Lucite Zimbabwe	1.75	0.64	0.38	89.00	1.50	93.27	27.9
Buzi Zimbabwe	2.44	2.35	1.31	103.00	2.00	111.10	33.2
Sub-total ZWE	4.51	2.99	1.98	253.00	5.90	268.38	80.3

Upper Revue	0.96	28.40	0.36	2.00	0.50	32.22	9.6
Middle Revue	0.67	–	0.34	2.00	0.30	3.31	1.0
Lower Revue	0.67	–	0.41	3.00	0.40	4.48	1.3
Upper Lucite	0.54	–	0.47	1.00	0.20	2.21	0.7
Lower Lucite	0.54	–	0.23	1.00	0.10	1.87	0.6
Upper Buzi	0.93	–	0.63	1.00	0.20	2.76	0.8
Middle Buzi	0.72	–	0.47	–	0.30	1.49	0.4
Lower Buzi	0.72	–	0.25	14.00	2.70	17.67	5.3
Sub-total MOZ	5.73	28.40	3.16	24.00	4.70	65.99	19.7

TOTAL	10.24	31.39	5.14	277.00	10.60	334.37	100.0

The urban sector in Zimbabwe is the largest water user (43%) followed by crop irrigation (Figure 9)

Figure 9: Contribution of the various sectors to water demand in Buzi Basin

Pungwe Basin

Table 4: Current water uses (Mm³/yr) by various sectors in the Pungwe Basin

	Urban	Rural Water	Irrigation	Livestock & Tourism	Industry	Total	% of Total
Pungwe Zimbabwe	112		66			177	22
Honde Zimbabwe		11	42			53	7
Sub-total ZWE	112	11	107	–	–	230	28

Upper Pungwe			5			5	1
Nyazonia			75			75	9
Middle Pungwe		9	44	5	32	90	11
Muda			34			34	4
Lowe Pungwe	92		276		7	375	46
Sub-total MOZ	92	9	434	5	39	579	72

TOTAL	203	20	541	5	39	808	100

Water used for rural water supply and livestock watering amount to 3% of the total water use in the Pungwe Basin (Figure 8).

Figure 8: Contribution to water use by the various sectors in the Pugwe Basin.

Save Basin

Figure 10: Contribution of the sectors to water use in the Save Basin

Table 6: Estimated amounts (Mm³/yr) of water used by the various sectors in the major sub-basins of the Save Basin.

Sub-basin	Irrigation	Urban	Rural	Mining	Livestock	Others	Total	% of Basin Total
Save Zim	1 838	14	81	5	210	25	2 174	28
Runde	5 190	63	54	16	153	4	5 480	70
Sub-total ZWE	7 029	77	134	21	363	29	7 653	98

Massangena	43	4	3	40	1	3	93	1
Covanne & Estuary	94		3		1		97	1
Sub-total MOZ	137	4	5	40	2	3	191	2

Basin Total	7 165	81	140	61	365	32	7 844	100

WATER QUALITY

Buzi

Figure 5: Places where the measurement of water quality indicator parameters was carried out in Buizi river catchment (source: Steinbruch, 2016).

Table 2: pH, turbidity, microbial and nutrients in water courses in Buzi river catchment (Steinbruch, 2016).

Sub-basin	Station	Local	pH	Total coliforms [UFC/100 ml]	Turbidity [NTU]	NH₄ [mg/L]	N0₃ [mg/L]	P [mg/L]
High Revue	19		7.6-8.5	1-100	2.72-5.59		7
	20		7.6-8.5	1-100	2.72-5.59		7
	21		7.1-7.5	1-100	47.61-80.20		7
	22		7.1-7.5	101-240	47.61-80.20		8
	23		7.1-7.5	1-100	2.72-5.59		8
	24	Chicamba reservoir	7.6-8.5	1-100	2.72-5.59		9
	25	Entrance of the Chicamba reservoir from Zimbabwe	7.1-7.5	101-240	2.72-5.59		2
	26	Entrance of the Chicamba reservoir from Chimanimani Park	7.6-8.5	101-240	80.21-879		8
High Lucite	13		6.5-7.0	101-240	47.61-80.20
	14		6.5-7.0	1-100	2.72-5.59
	15		6.5-7.0	101-240	47.61-80.20
	16		6.5-7.0	101-240	47.61-80.20
High Buzi	29		7.6-8.5	1-100	2.72-5.59	1.1	8	0.1

Table 3: Concentration of heavy metals in water courses in Buzi catchment (Steinbruch, 2016). Values highlighted in red exceed WHO limits.

Sub-basin	Station	Local	Ni [mg/L]	Cu [mg/L]	Zn [mg/L]	Pb [mg/L]	Titanium [mg/L]
High Revue	19					0.001	0.008
	20			0.002			0.004
	21		0.009	0.002			0.007
	22			0.002			0.020
	23			0.002			0.003
	24	Chicamba reservior		0.002			0.002
	25	Entrance to the Chicamba reservoir from Zimbabwe	0.009	0.003			0.009
	26	Entrance to the Chicamba reservior from Chimanimani park	0.080	0.030	0.1	0.008	0.002
High Lucite	13			0.002		0.001	0.01
	14			0.003		0.003	0.02
	15			0.002			0.01
	16		0.003	0.004	0.004		0.007
High Buzi	29			0.003			0.002

Pungwe

Figure 6: Location of gold mines in Pungwe river (Source: GoM, 2006)

Save

Table 4. Chemical parameters of surface water sampled in Save and in Runde catchments, a tributary of save in Zimbabwe, measured in Abril-May 2013. Values highlighted in red exceed WHO limits.

Parameter	Range
BOD	<2-36.8 mg/L
COD	<1-109 mg/L
DO	66.6-226.9 µg/L
Cl	11-58.2 %₀
Cu	0.01-0.02 mg/L
NO₃	0.55-1.46 mg/L
TSS	2-462 mg/L
Fe	0.02-3.37 mg/L
Cu	0.01-0.02 mg/L
Mn	0.01-0.28 mg/L
Ni	<0.01 mg/L
Zn	<0.01-0.02 mg/L

Table 5: Chemical parameters of surface water sampled in Save and in Runde catchments, a tributary of save in Zimbabwe, measured in Abril-May 2013. Values highlighted in red exceed WHO limits.

Catchment	Station	Chloride [mg/L]	Sulphate [mg/L]	Nitrate [mg/L]	Ammonia [mg/L]	Fe [ppm]	Ni [ppm]
Save	CHIPIN	21.3	11.8	0.204	0.012	0.68	N/D
Save	DTZ 1	7.1	112.8	0.003	0.014	0.53	N/D
Save	EL 2	21.3	144.2	0.032	0.027	1.39	N/D
Save	EPR 106	7.1	74.5	0.041	0.025	1.50	N/D
Save	ER 13	14.2	48.3	0.007	0.015	1.67	N/D
Save	ER 13 A	35.5	30.3	0.003	0.106	2.30	N/D
Save	ER 49 A	7.1	19.9	0.005	0.014	0.94	N/D
Save	ER 56 A	7.1	12.6	0.034	0.015	0.37	N/D
Save	ER 86 A	63.8	49.2	0.165	0.103	0.99	N/D
Runde	EL 7A	7.1	23.4	0.024	0.011	0.10	N/D
Runde	ER 118C	7.1	24.2	0.007	0.014	0.11	N/D
Runde	ER 1A	70.9	15.2	0.054	0.010	0.45	N/D
Runde	ER 30A	14.2	0.0	0.009	0.010	0.55	N/D
Runde	ER 3A	21.3	16.9	0.007	0.011	N/D	N/D

N/D: stands for not detected. Values in red had exceed the WHO standards (source: Murwira et al. (2014)).