The Kano Physical Environment

Prof. Kabiru Ahmed
Department of Geography
Bayero University, Kano, Nigeria
Previously written also for www.kanoonline.com, which was sponsored by Kano Forum (Inuwar Jama’ar Kano), Kano, Nigeria

KANO ENVIRONMENT
The Kano Environment refers to an administration area known as Kano State.  It is so called because the state capital is named Kano.  The environment covers an area extending between latitudes 120 40’ and 100  3O’ and longitude 70  4O’ and 90  30’.

GEOLOGY
There are three major rock formations namely the basement complex rocks comprising of crystalline igneous and metamorphic rocks dating back to the Precambrian age.  Younger granite rocks were intruded later in the Jurassic.  The youngest formation is the Chad sediment deposited from the quaternary including recent deposits(Fig 1).

THE BASEMENT COMPLEX
Rocks of the basement complex underline over 70% of the Kano environment.  The rock types in the area are older granites, met  a sediments and older basement.  The older basement is composed of migmatite, biotite gnciss, and blanded gneiss.  Migmalite is composite gneiss produced by injection of granite magma in to schist host. Gneiss is metamorphosed granite and is granitic in composition while a biotite gneiss is a foliated crystalline rock with high biotite content.  Banded gneiss has light and dark bands with a light fraction of quartz while the dark fraction or band consists of biotite, plagioclase and quartz minerals.

The ancient metasedimentary rocks result from the weak metamorphism  of sedimentary rock.  Rock types include Phyllite which is derived from metamorphism of clayey sediments.  It is intermediate in metamorphism between slate and schist.  Quartzite metasediments results from cementation or fussion of quartz grains of sandstone.

Older granites are commonly biotite granite and granordiorite.  A biotite granite is an acid igneous rock with high content of biotite mineral while a granordiorite has a composition which is intermediate between a diorite ( an intermediate igneous rock) and a granite.

Joints and fractures in the Basement complex rocks are better developed in the granites and quartzites and less in the gneisses, and migmatites, Joints rarely extend to depths greater than 90 metres.

THE YOUNGER GRANITE
Occurance of Younger Granite corresponds to basement joints and fracture system.  The systems guided volcanic eruptions and the granite instruded as high level magma chambers beneath volcanic centers. It is for this reason that the younger granite ring-complex structure formed.  Large quantities of volcanic rhyolite lava is still preserved in southern part of Kano state. Rhyolite has the same mineral composition as a granite (quartz, feldspar, and mica)  but it has minute crystals due to rapid cooling of magma.

Besides rhyollite extrusive there are also instrusions of granite-porphyry and biotite granite. The instrusions form the ring-complex and are more resistant to erosion than most of the rocks of the basement complex.  This is the reason they form a series of hill massifs rising over 1000 meters above sealevel.

The younger granites have low magnesium content and this facilitated the crystallization of iron bearing minerals such as fayalite and olivine, hedenbergite as pyroxene and riebeckite and amphibole.  Cassiterite or tin is abundant and associated with the biotite-granite. Erosion concentrated the tin in colluvial deposits to provide sources for the tin mining industry.

The younger granites are strongly jointed arising from reagional compression with the stress producing fractures which break outcrops into blocks.  These vertical or near vertical joints are usually independent of the local instrusive structure.

THE CHAD SEDIMENTS
The rocks are freshwater sediments of lacustive and fluviatile clays, sandy clays and silts with beds and lenses of sand and gravel at various levels.  These are overlain by more recent sand drift and alluvium. Chad sediments are found in the northeast where unconsolidated aelolian sand form a drift plain.  The alluvial sediment is related to the channel of the Rivers Hadejia, Jakara, Thomas and Gari.  In the former causes of these rivers the ancient alluvium is almost overlain by drift material while recent alluvium occurs along the existing water causes.

ENVIRONMENTAL RESOURCE
The distribution of rock types have considerable significance in three main respects. The availability of tin which was concentrated in transported regolith attracted colonial mining companies and tin was mined for export from the Ririwai area of granite ring complexes. The mining companies left when it became less attractive.  It is believed that this area still has some potential.  Some rare earth elements are also reported to be abundant here.

 Groundwater potential is higher in the chad sedimentary area because of the limited depth of weathered regolith in the basement area, which is 15m to 30m.  Joints and fractures are only important when open instead of tight cracks.  In general joints are less developed in the metamorphic rocks. The characteristics of landforms also depend on the nature of rocks and this point is highlighted in the next section.

LANDFORMS
PLANTATION SURFACES          
Pugh and king (1952) and Grove (1957) described plantation surfaces in Nigeria  at 4000ft (1300m), 2,200-2500ft(733-833m), 1600ft (533m), and 1000ft (300m).  In addition, Grove identified two lower levels at 400ft (130m) and 250ft (83m) in the Benue Valley.  Planation surfaces in the Kano plans were identified by Bawden et al, 1973.  The geomorphological history of the plains has been traced to the Jurassiz when the Gondwana Planation surface existed and the younger granites were instruded below the surface.  The planation surface was faulted in the late jurass or early cretecems (135million years before present) and the Benue and Niger trough as well as the Sokoto and Chad Bassis were formed.
The Gondwana surface (1333m) was eroded and a Post-Gondwana surface (833-733m) formed by the late cretateous.  The planation exposed the resistant younger granite to form hill massifs.  Remnants of this surface may be traced on the hill massifs in the south of Kano State.
An African planation surface (533m) was formed following a major cycle of erosion in the Miocen (11 million years before present).  A post-African planation surface (300m) was formed in the Pliocene (some 7m years before present).

POST-GONDWANA SURFACE
This is in the south of the state and young granite massifs stand above the planation surface which is at over 730meters.  Relief is about 100 meters while average slope is about 40 because of the frequent hill slopes (Fig 2a).  The highest drainage density of about 2 km/km2 is recorded here where there is a relatively higher rainfall and steeper slopes.  This is rated as an area of high erosion harzard with a hyposometric integral of about 49% (Ahmed, 1987).

AFRICA SURFACE
The surface is below the Post-Gondwana surface at about 533m and a relief of about 30m. The average slope is 1.50  and drainage density  is 0.8-1.2 km/km2.  It is an extensive area of moderately high erosion hazard with a hyposometric integral of 45-55%.

This surface is protected under the falgore forest/game reserve resulting in an extensive interfluve plain with limited drainage and slope development.  Here, the average slope is 10 while drainage density is 0.7km/km2.  Hypsometric integral is highest at 62% indicating limited surface exhumation and moderately low erosion due to the protective function of trees.

The Africa Planation surface is illustrated on Fig 2b in the River Kano Catchment while most of River Challawa Catchment is also within the Africa Surface.  The boundries separation the Post-Gondwana surface and the Africa surface is a stripped scarp.  Surface strippling is more pronounced along a scarp separating the Africa Surface and the Lower Post-Africa Surface.

STRIPPED SURFACE
This surface stretches from the headstream areas of the Rivers Iggi and Dogwalo below the River Kano Africa Surface, to the headstream areas of the Rivers Jakara, Thomas and Gari below the River Challawa Africa Surface (Fig 1).

Surface stripping and slope replacement have lead to the formation of erosion residuals, with boulder slopes(7-15), rubble slopes (4-70) and lower concave slopes (2-4O) and (1-3O).  Granite hills are common in the Iggi and Dogwalo headstream while mesas are common in the Thomas and Gari headsteam areas (Fig 3).  The average slope is 40 while drainage densities reach 2km/km2 with a hyposometric integral below 50%.  Erosion hazard is rated as high because of the considerable relief and moderately steep slopes.

POST-AFRICA SURFACE
Surface uplift and erosion lead to formation of a new planation surface during the Pliocene. This surface is below the stripped hilly land at about 490-460m (fig 2c).  Extensive sheets of ironpan were formed in the Pliocene and later in the pleistocene which is overlain by drift material which may be up to 2m thick.

The surface has a gentie slope of 10 with the lowest drainage densities of 0.5 to 0.8 km/km2.  Hyposometric integral is 53-67% while erosion hazard is estimated as moderate because of the gentler slope, lower annual rainfall, and higher sand content in the soil.

EROSION
GULLYING
Land degradation is said to be severe where gullies are common.  This is the case in the Post-Gondwana surface where gullies are common on the younger granite hill slopes.  Gullying is also common in the stripped surface between the Africa Surface and the Post-Africa Surface.  Gullies in the stripped surface are associated with granite hillslope, mesa hillslope, and valley slopes with gradient of 30-60. The gullied hill slopes are 40- 150.

Gullies are less common on the Africa Surface and the Post-Africa surface where the catchment area gullied is 0.4 to 2.9% and 0.07 to 0.15% respectively.  There is more gullying in the Africa Surface because of the higher annual rainfall and higher silt-clay content in the soil. Infiltration rates varies from moderately slow to moderate (0.9-4.8 cm/hr) in Africa Surface to moderate and moderately rapid (6.5-14.7 cm/hr) in Post-Africa Surface (Anon 1981).

SLOPE WASH
Erosion measurements show that a minimum of 95mm of cumulative rainfall is needed for detachment and transport of soil particles to start, (Fig 4).  This erosivity level is reached around June in the Africa surface and July in the Post-Africa surface. The 95mm of rainfall is the moisture needed to reflenish soil moisture deficiet and to generate surface runoff. Runoff coefficient is also high in Africa Surface at 16-17% (140-150mm) than in the Post-Africa surface at 4-10% (30-60mm).

Slope erosion was estimated at 0.5mm per year (Brabber, 1975) and 0.22mm per year (Ahmad and Musa, 1990) from  reservoir sedimentation rates.  Erosion rate is higher where the rainfall erosivity and runoff coefficient is highest. Accelerated erosion arising from human activities need to be controlled through sustainable land management practices.

CLIMATE
SEASONS
The climate is determined by the movement of two air masses, a moist rather cool southerly mass known as south-westlerlies and a hot and dry northern air called the north-easterless.  The moist southern air forms a wedge under the lighter dry air and the region where the two air masses meet is primarily an area of pronounced moisture gradient. The humidity gradient is called the intertropical discontivity (ITD).

The annual motion of the ITD is northwards between February and August and southwards between September and January.  The north-south movement of the ITD influences weather pattern.  Maximum  rainfall is recorded in an area of considerable disturbance (air movement) 8 to 90 southwards of the ITD.  However, when disturbance is limited or when the northward movement of the ITD is restricted drought  is recorded.  The level of disturbance and the northward movement of the ITD is influenced by the global pattern of pressure and winds as well as the  interaction of the surface air and the upper air mass ( the jetstreams).  When the ITD is southwards, the state is under the north easterlies and there is weather change.  The weather changes arising from the movement of the ITD gives four seasons.

(i)         HOT AND DRY SEASON (Rani)
The ITD starts its southward movement in February and between March and May it has no considerable influence in the state and the weather is hot and dry during rani season.  The mean temperature is 28 to 300c while this is the season when the “false” start of the rain is recorded in May.  A few rainfall is recorded in May and rain days are separated by days of dry spell and less than 1% of the annual rainfall is recorded in May.

(ii)        WARM AND WET SEASON (Damina)
The ITD has by now made considerable advance northward and there is widespread rainfall in the state.  Rainfall occurs mainly in the evenings for periods of one to three hours and considerable heavy rainfall (high intensity) is recorded in the first forty minutes of rainfall occurances.  Over 90% of the annual rainfall is recorded in this season.

This is the humid period when surface runoff is available for streamflow and soil moisture in sufficient for plant growth.  Damina is the crop growing season when grains and legume are grown.

Temperature drops to an average of 240-290c while evaporation is lower because of the higher relative humidity of the moist south westerlies air.  This is why the runoff-coefficient is highest during this season.

(iii)       WARM AND DRY  SEASON (Kaka)
The ITD is now in its southward retreat and only a few slowers may be recorded in October accounting for less than  8% of the annual rainfall.  This is the harvest season between October and November when farmers are busy harvesting crops and traders are buying what is offered.

Average temperature is 28-290c and this is a dry season as evaporation is in excess of rainfall.  This is a season when soil moisture is depleted and stream flow recedes.

(iv)       COOL AND DRY  SEASON (Bazara)
The ITD reaches it southern limit during this season and the state is under the influence of the north easterly wind which brings a cool and dusty weather called ‘Harmattan” between December and February, the dry air from the north brings no railnfall but the transforted harmattan dust is deposited to replenish soil nutrient. The depth of the windrift material varies from an average of 1 to 2m.

This is the cool season when temperature is 25 to 270c.  The skin dries up during this season and special care (LOTION) is needed for protection against cold.  Respiratory problems are also experienced and athma patients are particularly hard hit.  The cool temperature makes the season suitable for wheat cultivation under irrigation. Wheat is an important crop in the Kano River Irrigiation Project.

Seasonality is an important aspect of the climate, it determines the length of the crop growing period.  At another level, the variability of the annual rainfall during the rain season (Damina) has important management implications.

RAINFALL VARIABILITY
Annual rainfall is closely related to latitudinal position with over 1000mm recorded in extreme south and about 7800mm or less in the north because the southern part is under the influence of the south easterlies for a longer period.  The mean annual rainfall at Kano between (1988 and 1999 is 823mm.

Mean annual rainfall recorde at Kano shows above average rainfall from 1905 to 1939 with means of 934.02mm (1905-1909), 813.67mm(1910-1919), 861.59(1920-29), and 934.84 between 1930 and 1939.  The rainfall was below average in the 1940’s with an average annual rainfall of 770.00mm.  It increased to above average in the 1950’s(918.78mm) when the level of 1930’s was reached.  The rainfall declined gradually from 1950’s to 1960’s (816.90mm), 1970’s (701.24mm) and 1980’s(670.79mm). During the three decades 1960’s to 1980’s there were recurrent droughts and the decades were considered as periods of increased aridity.

From 1988 when 1049.2mm was recorded, the rainfall assumed an upward trend and a mean of 810.48mm was recorded between 1990 and 1999.  During the three dry decades (1960’s-1980’s) there were only two incidences when the annual rainfall reached up to 1000mm at Kano in 1962(1139.4mm) and in 1988(1049.2mm).  In one normal decade (1990’s) when average rainfall was recorded, there were two incidences in 1991 (1096.7mm) and in 1994(1296.1mm) when the annual rainfall reached 1000mm.

The trend show that rainfall is highly variable and the rain season could either start late or end early or both depending on the north-south movement of the ITD. During the recovery limb from 1988, there were years when flood was recorded while in other years drought was recorded.  The most extreme events were the floods in 1988 and the drought in 1989/90 (Table 1).

TABLE 1.  ANNUAL RAINFALL AT KANO

 The floods in 1988 were destructive and residential areas were badly affected as several houses collapsed, other properties were lost all totaling millions of Naira.  This was attributed to heavy rainfall(1049mm) which resulted in heavy runoff, and indiscriminate dumping of waste which blocked drainage causing flooding.  The buildings which collapsed were mainly constructed of mud. The congested part of metropolitan Kano was most devastated because of the poor maintenance of drainage structures, high generation of waste in excess of what is evacurated as well as haphazard construction of structures close to water ways.  The areas most affected were the city wards of Yakasai, Zango, Kududdufawa, Kofar Wambai, Kulkul, Dala and Madatai.

The 1988 heavy rainfall also facilitated the collapse of Bagauda Dam, constructed to supply water to metropolitan kano.  The earth dam was constructed between 1969 and 1970 while it started to fill in the 1970/71 rain season.  It was designed to store about 22.14m3 of water but it collapsed between 15 and 17th August 1988.

The collapse is partly attributed to structural defects because in 1986 longitunal cracks were noticed and the spill way was lowered to reduce the maximum water level of the reservoir by 4m(about 30% lowering).  Again early in 1988 ant holes were dug out and refilled with sand. In early 1988, the maximum water level was restored because it was assumed that all was well with the structure. The maximum water level was reached on August 15, 1988 when about 78.8mm of rainfall was recorded. A  heavy downpour (56mm) was recorded on August 16th, which facilitated the collapse of the dam. (Ahmad and Musa, 1989).

Following the destruction in 1988 measures were put in place to prevent similar occurrences. Bagauda dam was reconstructed while the larges Tiga Dam with a Maximum water level of 31.48m was reconstructed and the emergency spillway was widened from 100m to 300m and was lowered to 3.5m lower than the concrete spillway.  As a result of the storage capacity of the reservoir was reduced by 600x106 m3.  Urban flooding was to be arrested through mobilization of people to participate in clearance of drainage channels through self-help efforts.  The activities of the Kano State Refuse Disposal Agency (REDA) was intensified and made more effective in removal of waste. These effects have paid well and heavy rains recorded in 1991, 1994 and 1998 (Table1) have not caused considerable damage.

The three dry decades (1960’s-1980’s) attracted national and international attention. At the National level, the Federal Ministry of Agriculture conducted a survey of dissertification while at the international level a UN conference on desertification was held in 1977 and the UN convention to combat desertification was launched in 1993. In Kano State drought was recorded in 1962/63, 11972/73, and 1983/84.  These droughts resulted in water shortage and crop failure. The drought of 1989/90 is the most recent drought with considerable record of crop losses.

In 1990 it was reported that about 75% of farms were affected by drought in Kano State and 1.2 million tones of grains was lost valued at N1.82 billion.  The yield of sorghum was reported to decline from 0.71 tonnes/hectare in 1988 to 0.41 tonnes/hectare in 1990 which is a 56% decrease.  This is similar to the yield decline of 40-60% in the north and 20-40% in the sourthen part of the state due to drought in 1973(Report on the Drought Phenomena in Kano State, Ministry of Works and Survey, 1974).

Rainfall in the state is highly variable.  Long term trends have not been identified, the speculation of a ten year drought cycle cannot be proved based on the short records from 1960-1989.  Similarly, it has not been possible to predict, daily, monthly, and annual rainfall.  This means farmers have to cope with considerable planning uncertainties while communities and the Government need to plan against flood and drought hazards.

DRAINAGE AND HYDROLOGY
WATER RESOURCES POTENTIAL
There is considerable relation between geology and drainage pattern with the highest network of rivers in the basement complex area.  The small areas of Chad Sediments in Danbatta and Gaya Local Government Areas have groundwater potential with limited channel development.  The drainage systems are the rivers Kano, Challawa, Iggi and Gaya in the South while Rivers Gari, Thomas, and Jakara are located in the north.

These rivers are dammed to store water in surface reservoirs for multi-purpose use including irrigation, domestic supply, fisheries and recreation. Irrigation development is well advanced along the Rivers Gari, Thomas, Jakara and Kano (Kano River Project – Phase 1).  While the famous holiday resort at Bagauda (the lake hotel) and Tiga Rock Castle are located along the Two dams in the River Kano Catchment (Bagauda and Tiga dam reservoirs).  The Bagauda lake hotel was recently converted to accommodate a campus of Nigerian Law School as well as the Federal School of Tourism.

Water Resources development in the state was fully pursued   after formulating a fifteen year water resources master plan convering between 1970 and 1985.  At the end of the plan period 22 dams were constructed and hundreds of boreholes sink.  The state now has 25 small and large dams (Fig 5) while the rural development agency (KNARDA) continued to sunk boreholes until of recent when drilling activities is commercialized to generate revenue.

Groundwater potential is higher in the limited areas of sedimentary rock and it occurs in perched aquifers as well as in confined and semiconfined aquifers. The potential is low in the basement complex area and the success ratio of boreholes is lower because of the limited depth of regolith, its clay content, and the localized occurances of factures and joints.  However, the basement area has higher surface runoff potential.

STREAMFLOW CHARACTERISTICS
The streams are seasonal and have flash flows with flow rising and falling in response to rainfall occurrences.  The high flash flows exceeded 10% of the times are recorded mainly in July and August in response to rainfall events of 30mm or more.  Such heavy rainfall storms are capable of generating high flash flows even at the beginning of the hydrological year, this is attributed to the high intensity of the storms.

Analysis of flash flows (exceeded 10%) and daily rainfall showed a significant correlation (r=0.63) and the relationship is expressed as follows for River Jakara (620km2):

Q         =          3.93+0.1X
Q         =          Daily discharge (m35
X         =          24 hours rainfall (mm)

For example when an average of 4.8.8mm was recorded the flow increased to 9.06m3S for it to fall within 24 hours.  When 41.2mm was recorded the flash flow was 8.07m3s and when 37.6mm was recorded the daily flow was 7.64m3s.

At the beginning of the hydrological year between April and June there is high evaporation and high soil moisture deficiency. The interaction of rainfall and evaporation suggest a moisture deficiet not to mention the high infiltration rates. This suggest that stream flow during this period is largely from exceptionally heavy rainfall storms. Less than 20% of the annual rainfall and less than 5% of the annual river discharge is recorded during this period when runoff coefficient is less than 2% and the coefficient of variation of mean daily discharge is very high at 121 to 212. The high variation of flow is due to the isolated occurrences of 24 hour flash flows as well as flow interruption
during which it is common to record no flow for periods of one to two weeks.  Flow interruption is due to the occurrence of rainfall dry spells. This period is termed a hydrological phase of interrupted flow.  There is high concentration of flow between July and September when about 94% of the annual rainfall  and 85 to 90% of the stream flow are recorded.  The highflows exceeded 10% of the times are mainly recorded during this period due to the more frequent occurances of rainfall storms up to 30mm. The peak discharge is also always recorded during this period.

The runoff coefficient is higher at 9 to 24%  while the coefficient of variation of flow is lowest at 57 to 76.  Streamflow is mainly made of quickflow component due to the higher response of the catchment to rainfall input from the expanded runoff contributing area.  This is a humid phase of continous flow and generally rising discharge.

About 1% of the annual rainfall is recorded between October and November/January and about 25% of the annual discharge is recorded.  Streamflow, in the absence of rainfall, is sustained from base flow as the subsurface moisture storage is depleted.  This means, there is a generally falling discharge while run off coefficient is high at 39%.  The coefficient of variation of mean daily discharge is high at 96 to 110.  This a posthumid phase of continous flow and generally falling discharge.

 There is an arid or dry hydrological phase when there is no rainfall and no streamflow between January/February to March.  During this period there is total dependence on groundwater.

The programme of dam construction was persued with vigour in the 1970s and there are 25 surface reservoirs today.  This has modified the stream flow regime.  There is flow in the channels during the arid phase generated not from rainfall input but from reservoir releases.  The release is used for irrigation as well as domestic supply. There is also less flooding down stream of the reservoir because the flow or release is regulated.

HYDROLOGICAL AREAS
In the basement complex area, the USDI (1968) identified two hydrological areas as the upland area and the Gari area corresponding to the Africa surface and the Post-Africa surface.  The upland area comprises of Rivers Kano, Challawa, Iggi and Gaya.  While the Gari area comprises of Rivers Gari, Thomas, and Jakara.  The upland area receives higher annual rainfall (Over 800mm) than the Gari area (less than 800mm). 

Runoff coefficient is higher in the upland (16-19%) than in Gari (4-9.6%).  The mean unit runoff is similarly lower in Gari (0.39 to 0.63m3s/km2) than in upland (1.45-1.77m3s/km2) .  Peak discharge is also higher in upland because of the higher rainfall and larger catchments.  Peak unit runoff varied from 0.07-0.14m3s/km2  in the upland to 0.01-0.03 m3s/km2  in the Gari area.

In the Chad sedimentary area, which is of limited extent, there is virtually no surface drainage because of the high transmission losses.  This means there is no reasonable surface water potential here.  Infiltration rates are high while runoff coefficient is low.

Groundwater regime was more favorable before the dry decades ( 1960’s-1980’s) when water level in village wells was 10-12m deep in the upland and about 2m in the lowland (fadama).  During the dry decades wells dried up and there was fadama desiccation.  The water level dropped to 20-25m in the upland and 8m in the fadama areas except for the fadama areas which are irrigated and have water  levels of 0.5-2m.  The wells now need to be dredged each dry season while for wells experiencing heavy abstraction there is need for abstraction to stop for some hours for the well to recover or be recharged.

WATER QUALITY
Stream water samples were analyzed in 1966 and 1967 by USDI (1968) who concluded that stream water was of good to excellent quality.  It had low total dissolved solids, below 200mgl, low sodium absorption ration (0.14-1.1) and non-toxic concentration of baron.

The analysis of sediment concentrations during 1996, 1967   and 1987 suggest that concentration of suspended sediment is influenced by rainfall erosivity as well as the protective function of forest reserve.  On the other hand, the concentration of suspended sediment increased due to the increased use of agrochemicals.

The average size of rainfall storms varied from 13mm in 1966, 14mm in 1967 and 12mm in 1987. The frequency of heavy erosive storms (up to and more than 30mm) was three occurrences in 1966, four in 1967 and only one storm in 1987.  These figures suggest highest erosivity during 1966 and lowest in 1987.  The erosivity calculated as the ratio of the square of the highest monthly rainfall to the annual rainfall varied from 1.94 in 1966 to 4.34 in 1967 and 2.09 in 1987 confirming lowest erosivity in 1987.  Sediment concentration in 1987 was lowest due to the lower mean suspended sediment load in River Challawa (5933.5 mgll in 1966 and 810.5mgl in 1987), and River Kano (687.1mgl in 1966 and 132.6mgl in 1987).  The difference is attributed to the lower rainfall erosivity.

The lower sediment load of the River Kano is due to the extensive area of woodland, falgore reserve (about 370km2) which protects the catchment slopes from erosive rainfall.  Sediment analysis showed higher sediment concentrations from a cultivated tributary catchment than from the protected catchment.  The suspended sediment concentration was higher (200 mgl) from the cultivated tributary compared to the negligible suspended load from the protected catchment (Ahmad and Musa 1991).

The dissolved sediment in 1987 was found to be higher than in 1966 in River Challawa with 13547 mgl and 47.5mg/l respectively  and in River Kano to 331.40 mg/l  44.29mg/l respectively.  The increase was explained to be due to the increased use of agrochemicals with irrigation development (Ahmad and Musa, 1991).

Stream sediment load was sampled again to analyse runoff between June and September 1995 and irrigation water between October 1995 and January 1996.  The lowest concentration of runoff sediment was in protected falgore reserve (132-240 mg/l) and from rainfall sample (50-92 mg/l) contributed from atmospheric dust.  Sediment concentration decreased considerably in the irrigation season which has very low concentration of dissolved sediments (63-130mg/l) attributed to the siltation in dam-water reservoirs.  The dissolved sediment concentration was still higher than in 1966 (pre- irrigation).

The highest concentration of dissolved sediment was recorded at Kumbotso sampling site out of the eight sample sites. Kumbotso receives industrial discharge.  The high concentration of trace elements (copper cadnium, and iron) in irrigation water is attributed to the industrial discharge (Ahmed, 1998).

Largely untreated industrial waste flow into River Salanta a tributary of River Challawa. Water samples from Salanta showed levels of nitrates and phosphates above the maximum limits set by the Federal Environmental Protection Agency (FEPA) (Abdullahi et al, 1993) while the presence of bacteria in the water  could cause cholera, typhoid and dysentery.  The Salmonella species known to cause deadly typhoid was identified in the water in addition to chlorono-bacterium.

Tanko (1989) identified concentration of heavy metal (iron,lead, magnesse  and chromium) in excess of the permissible limits set by FEPA.

Industrial waste is also discharged in to the River Jakara which, as a result, suffers considerable pollution (Sokoto, 1981).  The proliferation of more industrial estates and the increased discharge of effluents in to rivers constitute serious environmental hazard.

The use of industrial liquid waste for irrigation consitute great danger to the soil and the crops.  An assessment carried out by Ikara (1997) showed highlevels of magneese, lead and iron in water application as well as in the irrigated soil.  A similar study attempted an assessment of the effect on ground water pollution.  The study showed tolerable levels of mercury (0.05mg/l) and lead (less than 1 mg/l) in River salanta upstream of the site where effluent is discharged into the river.  At the point of effluent discharge, the levels increased above the permissible limits of 17.5mg/l of mercury  and 20.5mg/l of lead.  The water used for irrigation had the highest concentration of lead (28.5 mg/l) and mercury (405mg/l).  However, samples of shallow well water showed low levels of mercury and lead suggesting limited or no groundwater pollution (Sa’ad, 1995).

SOIL AND VEGETATION
SOIL GENESIS
The zonal soils are the ferruginous tropical soils whole equivalent is nitrosols (FAO), Ultisols and Altisole (US Dept of Agric) and Latosols (General).  They are the normal product of soil development on the acid crystalline rock.  The soils have marked differentiation of horizons, frequently has a leached A horizon and always contain a textual or structural B horizon.

The soil has appreciable reserves of weatherable minerals with moderately low CEC.  Clay is mainly kaolinite but small amounts of illite may be present.  Free iron oxides may form mottles and concretions.  Differences from the dominant characteristics are attributed to other soil farming factors.  For example, in the dry areas where there is appreciable amount of sand drift, there is developed what is known as the brown and reddish brown soils of semi arid areas.

The brown and reddish brown soils are called Xerosols (FAO, UNESCO), and Aridisols (US Dept of Agriculture).  The soil exhibit profile development heaving a textural, structural or colour B horizon.  There is considerable reserve of minerals due to the slight weathering and leaching arising from low rainfall.

Time factor is also important and there are juvenile soils with very weak or no definition of genetic horizons because of the young age of the soils.  There are two subdivisions of juvenile soils due to the nature of the parent rock.  There are those on riverine and lacustive alluvium as well as those on aelolian sands.    There are more extensive areas of alluvial soils in valley bottoms and floodplains.  These soils are varied in their texture and drainage characteristics.  Site factor is important because on steep slope, erosion and mass movement limit soil development.  In this case the weakly developed soils are called lithosols. Hillslope soils are predominantly skeleton with no horizons and containing stones within 30cm of the surface. Soil may contain considerable amounts of quartz or lateritic gravel.

On poorly drained sites one finds hydromorphic soils.  These are in concave slope segments; the mineral soils exhibit no profile development.  They are vertisol soils, which show deep and wide cracks in the dry season due to high content of clay (more than 30%).

SOIL FERTILITY
The soils are deep, well drained except for hydromorphic soils, and poorly structured. The texture range from sandy loam in the south to loamy sand in the north.

Soil physical deficiency includes the occurrence of iron capping or hard crust.  The iron pan concretion limits rooting depth and the cap may be exposed as a result of severe erosion.  Iron pan is formed from the accumulation of iron liberated as a result of chemical weathering.  Iron accumulates and herdens due to dehydration and oxidation. Where accumulation is limited, the iron only forms concretions and mottles.

Hard surface crust prevents infiltration of water, thereby facilitating run-off and making the soil droughty.  It reduces the availability of water to plants as well as preventing the emergence of seedlings.  Crust formation is common in silty or very five sandy topsoil’s low in organ matter. It is due to the washing in of very fine soil particles to fill soil pores.

Soils are chemically rather poor with 80-90% sand and 2 to 4% clay content.  Soil PH ranges from 5.4 to 7.8 and acidity is said to be satisfactory.  Cultivated soil has very low organic carbon content at 0.21 to 0.3%.  This is due to the low input of organic matter (litter and manure).  The soil exhibits deficiency of nitrogen and phosphorus, which are largely released from the decay of organic matter which is low.  Total nitrogen level ranges from 0.02 to 0.04 while available phosphorus level is 5.0 to 9ppm.  This is why it is essential to apply manure as well as inorganic fertilizer (NPK and UREA) in cultivated areas in order to sustain fertility levels. The planting of trees also help to add more organic matter to the soil thereby enriching the soil.

SAVANNA VEGETATION
Savanna is simply described as closed grass or other predominantly herbaceous vegetation with scattered or widely spaced woody plants.  The climatically defined vegetation types in the state are the northern Guinea savanna and Sudan savanna.  Northern Guinea Savanna is an open woodland or bush land with grasses shorter than in the southern guinea where grasses are 1.5 to 3m tall.  The Sudan Savanna has scattered trees in open grassland with grasses under 1.2m tall.

The vegetation has been largely cleared for cultivation to form cultivated parkland. Parkland has scattered protected trees at some distance apart in open cultivated land.  Small trees and shrubs are more common on fallow land where regeneration may take place.  About 75% of the land is cultivated parkland with average tree densities of less than 25 per hectare.

Within the two broad types of vegetation identified, there are pockets of other structural types.  Thicket vegetation is found along large river channels and floodplains and it is described as impenetrable shrubby vegetation.  Surviving savanna woodland is found as forest/game reserve such as the falgore reserve (370km2).  Here the trees and limited number of shrubs form a light canopy.  Where the woodland reserve is degraded due to uncontrolled exploitation it changes into a scrub vegetation or bush which is made of shrubs and herb and it  is not closed.  Gazetted grazing reserves may be grassland where trees and shrubs do not exist. The grazing reserve is degraded, through uncontrolled exploitation, when woody vegetation encroaches.

SPECIES COMPOSITION
Natural vegetation covers less than 5% of the land area and even then it is largely degraded except for the falgore reserve which also suffers from encroachment. The over-riding human influence means that most tree species are common to both northerns Guinea and the Sudan Savanna.  Such common species include Adansonia digitata (kuka in Hausa) and Vitex domiana (Dinya) which provide edible fruits and leaves.  Diospyros mespiliformis (Kanya) and Tamarindus indica(Tsamiya) provide edible fruits while Moringa oleifera(zogale) provides edible leaves.

Other species found in the two areas but more common in the Guinea zone include Parkia clappertoniana(Dorawa) which has declined in the Sudan following the three dry decades, Anogeissus.  Leiocarpus(Marke) and Khaya segalensis(Madaci) are popular fuelwood species whose population has been decimated particularly in the Sudan.  K. senegalesis is good timber, fuel wood, medicinal and provides fodder in the dry season but it has virtually disappeared. Species which are more common in the Sudan include Ziziphus Spina-Chrisli(kurna), Hyphaene the baica (Goriba), Borrasus aethiopum(Giginya) and Balanites aegyptiaca (Aduwa) which provide eadible fruits. Others are the leguminous Acacia  species which supply livestock folder and fuelwood such as A. senegal(Dakwara), A. nilotica(Bagaruwa), A. Seyal (Dushe), and A. albida(Gawo).  Actively regenerating species on fallow land are Guiera senegalensis (Sabara), Hyphaene the baica (Kaba) and Piliostigma thonningii (Kalgo).

The tree species are under good management for their numerous economic as well as ecological benefits, and a few such examples are:

Parkia clappertoniana (Dorawa)
It is a common farm tree which grows to a height of 10-15metres and may reach 20 meters. The tree produces light-brown fruits after 8-10 years.  The fruit has black seeds covered in yellow pulp which is eaten while the numerous black seeds are fermented to form an important source of protein. The product, a black dried patties (Daddawa in Hausa) is sold and used as seasoning in vegetable soup.
The tree is good fuelwood species and it is used as pulp for manufacturing paper.  It is an effective tree shade tree and the leaves are shed to add  nutrients to the soil. It is more useful as a scattered farm tree.

 Tamarindus indica (Tsamiya)
 The tree reaches a height of 20 metres and has an evergreen, dense crown.  The fruit is a pulp embedding tiny brown seeds.  The fruit is sucked or mixed with water and sugar (if needed) to produce a vitamin-rich drink.  The pod is also soaked in water and the juice is mixed with millet and sorghum gruel to give it taste and make it more digestible.

The young leave is eaten by livestock while the termite resistant wood is used in making furniture.  It is evergreen and an effective shade tree.

Azadirachta indica(Darbejiya)
The tree grows to a height of 10-15 metres and has a wide, dense, evergreen crown.  It is mainly planted as a village tree for its shade and fuelwood supply.  Small branches are used as tooth brush.  It is highly resilient because of its deep roots and it coppices and pollards very well.  It does well either as scattered trees or in plantations and as greenbelt around villages or as shelterbelt.

Acacia albida (Gawo)
It is the largest of the Acacias.  It is fast growing, coppices vigorously and may reach a height of 30metres.  The wood is a common fuelwood and is an excellent source of fodder.

The tree has a reverse  foliage and retains its leaves during the dry season.  The leaves are shed at the beginning of the rainy season.  This means fodder is available when it is scarce in the dry season when most trees shed their leaves.  The leaves  and pods are eaten by animals in the dry season.  Shade is also provided when it is most needed.

It is a good agroforestry plant because it fixes nitrogen.  The plants   do not complete with crops for water and nutrients.  The reverse foliage means that there is no competition for light as crops are not shaded.

Acacia seyal (Dushe)
It is a deciddirous tree with bipinnate leaves.  It has sharply pointed spines of about 8m long like many Acacias.  Infact the name Acacia is derived from a Greek work “Alkis” meaning a pointed object in reference to the spines.  On the other hand, seyal is a latin form of an Arabic word meaning  “torrent”. The name is coined to donate association of the species with water courses.

The mature tree reaches 5 to 10 metres and has an open, spreading and flat-topped crown. It  also grows as a multi-stemmed shrub.  It is leguminous and may be prevalent under agroforesty systems.  It is a source of fuelwood and charcoal.  It provides gum, which is medicinal, is used to make ink as well as pesticides.  It is a good fodder as the leaves, twings, flowers, pods and seeds are eaten by livestock.  It recovers from moderate browsing and lopping to no more than one third of the branches.

Associated plant species include Acacia nilotica (Bagaruwa), Acacia senegal (Dakwara), Balanites aegyptiaca (Aduwa), Ziziphus spina-christi (Kurna), and Anogeissus leiocarpus (Marke)

RESOURCE MANAGEMENT SUMMARY
The state is mainly an area of basement complex rocks while erosion surfaces were developed following series of erosion cycles.  Erosion surfaces are generally undulating surface with gentle slopes (1-30) forming over 80% of the land area.  The extensive plain means that the state has high potential for agriculture.

Agriculture is largely limited by the variability of rainfall and in extreme years droughts are recorded as in 1931, 1944,1949,1956,1970,1972,1973,1983,1984 and 1990.  The growing season is limited to the humid rain season (Damina) and intensification is only possible through the development of irrigation.

The traditional irrigation depended on lifting water from water holes in dry channels to irrigate small parcels of land along river channels in the dry season. This system is known as ‘Shado of’ system or “Jigo” in Hausa.  Large area is irrigated using water pumps or by gravity irrigation using water releases from dam-reservoirs.

Under increasing population, land may have to be cultivated year in year out and in such cases external input is needed to sustain soil fertility because crop harvest deprives the soil of essential nutrients.  Under irrigation, the increased application of water may lead to water logging, salinisation and leading.
There is considerable release of untreated industrial waste which pollutes soil and water resources under irrigation.  In rural areas, over 80% of the people depend on fuelwood as a source of domestic energy for cooking and heating.  This means, farms trees are exploited and the input of litter may be affected.  Numerous problems have been listed which limit the productivity of the landscape. These problems need to be contained through effective management.

PLANT MANAGEMENT
About 90% of rural energy and 60% of urban supplies come from fuelwood.  The cutting of tree for fuelwood increased because of the high dependence and the increased use of vehicles, inplace of donkeys and bicycles, to transport over 90% of the fuelwood entering metropolitan kano.  A large proportion of the fuelwood is got from farmlands and farm tree densities are reported to decrease.  Other reports suggest stability because of tree planting, increased lopping instead of cutting whole trees, and the increased import of fuelwood from other states. There is also less dependence on land resources through increased diversification of livelihoods as well as emigration.

The forestry division of the Kano state ministry of agriculture pioneered tree planting campaign in 1972 to encourage the planting of farm trees and village trees as a response to the 1972 drought.  Tree planting campaign gained nomention under the Arid Zone Afforestation Programme (1977-84) set up by the Federal Government.  The campaign was conducted at four levels by the federal, state and local governments as well as conservation clubs.

The Ecological Disaster Programme (1986-89) was set up by the Federal Government and the state Government.  Under this programme, the state established 45km of sheltbelt, 80 hectares of rural woodots and 105 hectares of watershed plantations.  The World Bank assisted second forestry project was started in 1988 and ended in 1996.  The programme established in Kano State 406km of shelterbelt, 669km roadside planting, 361 hectares of orchard, 1191 ha of woodlot, and 1927 nuseries for seedling production (World Bank Implementation Report, 1997).  The planting of trees faciliate the protection of the soil against degradation as well as supplying fuelwood.

SOIL MANAGEMENT
A comparative study of soil management under small holder farming and large-scale irrigation in Kano State was carried out based on soil information for 1974 and 1988.  After 14 years of land use, it was observed that small holder farming was more sustainable because there was no change in particle size distribution as simple traditional implements were used which penerates to a depth of about 8.0cm.  Under large scale irrigation, there is more disturbance from the use of tractor-drawn ploughs which breaks soil aggregates and enhances erosion leading to the loss of silt and clay.  This means the landuse is less sustainable because of the tendency of the soil to become “single grain”(Essiet, 1990).

It is now observed that there has been changes in the management system under irrigation by increased use of organic manure.  As a result of this change, the soil texture has higher silt and clay proportions.  The fine sand soil is now sandy loam and sandy clay.  This means the landuse is more sustainable.  The problem which has developed is the increasing salinity and alkalinity related to poor drainage arising from the long term application of irrigation water.  In this case, it is recommended that all blocked drainage channels need to be opened (Tanko, 2001).

Small Holder farming system is also said to be most sustainable when manure is applied. Studies of the sustainability levels of small holder farm management practices showed that fallow system is unsustainable because of the persistent grazing by domestic animals. Fallow is supposed to help accumulate soil nutrients and to restore fertility but this never happens when the grass and weed cover is removed by grazing animals.  Similarly, the application of inorganic fertilizer is unsustainable, it only increases the level of nitrogen, phosphorus and potassium in the case of NPK fertilizer but does not add to the sustainability of the practice.  However, organic manure is found to be necessary because it improves soil structure and add nutrients through mineralization (Yusuf, 2000).

Studies of nutrient balance from the farming practices of three farmers showed that an average they applied 4.3tonnes per hectare of manure to achieve a balance of nutrient input and output.  The success of the practices relies on the integration of crop and livestock and the production of manure to fertilize the soil(Harris, 1996).

Soil management studies in Kano suggest that the application of manure is essential for the sustainability of small holder farming and of large scale irrigation. Long term fertility studies at near by samaru, zaria showed that small holder farming is sustainable when 2 tonnes per hectare is applied each year while the optimal application is 5 to 7 tonnes per hectare each year.  The application of manure leads to increases in the levels of carbon, nitrogen, and exchangeable calcium, potassium, and magnesium as well as cation exchange capacity.  The increase in nutrient level also means a corresponding yield increase.  When manure is not applied there is decline in nutrient level and crop yield.  When only 2 tonnes per hectare is applied the increase in fertility is very small and when 5 to 7 ha is applied the increase is rapid (lombin and Abdullahi 1977)

Manure is essential because of the gradual release of nutrient reserves, formation of soil aggregates, improvement of water retention characteristics, reduced nutrient losses through leaching because of increased exchange complex, and improving soil reaction.  It is instructive to add that agroforestry and tree planting adds organic matter to the soil while legume intercrop adds nitrogen to the soil.

WATER RESOURCE MANAGEMENT
The seasonality and annual variability of the water regime necessitated the development of water resources by way  of dam construction.  The dam structure needs to be managed in order for the water reservoir life span to be achieved.  For example, the Bagauda dam was designed to store about 22.14mm3 of water for irrigation, domestic supply, fisheries and recreation.  The dam started to fill in the 1970/71 rain season and by 1986 longitudinal cracks were observed while the southerned and of the embankment sagged.  The forestall any mishap, the spillway was lowered to lower the maximum water level by 4m or 30%. Later in 1987, ant holes were noticed and had to be dug and re-filled with sand.  The cracks were also filled with sand early in 1988.  This was not enough because excessive rainfall in August 1988 lead to the collapse of the embankment and the collapse of the dam lead to the destruction of farmlands, bridges and fish farms in the downstream. Reservoir sedimentation studies revealed storage loss of 0.9 to 0.13 to per year while 22.14Mm3 of the total storage capacity  was lost between 1970/71 and 1988. (Ahmed and Musa 1989).

This means that routine inspection and proper maintenance are neded to avert disaster. It is recommended to carry out intensive monitoring of embarkments as well as detailed reservoir sedimentation surveys.  It is suggested that state annual budget need to take into considering the special need to maintain the 25 dams and reservoirs.  Existing woodland reserves need to be protected in order to minimize sediment supply.  Dam construction is also associated with hydrological and morphological changes in downstream areas.  Olofin (1991) showed that the reduced streamflow downstream leads to channel incision and later stabilization of the former larger channel and the new incised channel.  This means erosion is minimized downstream.  The reduced flow also mean flooding may be eliminated or reduced in downstream areas and Nichol (1989) suggested that about 50% of fadama land may loose substantial moisture and this may necessitate land use change. This means that once a dam is constructed, the land downstream should be developed for irrigation using water releases from upstream reservoir.  The state government need to invest more to facilitate irrigation development in downstream areas.

Another water resource management problem that needs urgent attention is the issue of water pollution from industrial discharges.

Bichi (2000) indicated that Kano is a booming industrial center with over 320 industrial establishments comprising of chemical and cosmetic industries, tanneries, textiles, and food processing factories which release waste water into streams.  This according to Bichi, has lead to the deterioration of water quality in the state. Dada (1997) carried out industrial survey which showed that 60 industries discharged untreated effluent into rivers and only 6 industries surveyed (10%) had primary treatment plants ranging from oxidation tanks, to sedimentation tanks.  This is considered inadequate and water quality analysis showed excessive amounts of trace elements such as lead, chromium, iron and chloride (Ahmed, 2000).  These metals in desirable concentrations enhance plant processes such as protein and chlorophyll synthesis, respiration and nitrogen fixation.  In excess, they retard rot growth photosynthesis and drought resistance (conway and Pretty, 1991).

Stakeholders including industrialists, state and federal governments need to pool resources to set up a secondary treatment plant in order to eliminate excess, amount of trace elements contained in industrial discharges (Tables 2 and 3).

Table 2: TYPICAL TANNERY WASTE WATER CHARACTERISTICS

Table 3: TYPICAL TEXTILE WATER CHARACTERISTICS

 Source: KASEPPA

CONCLUSION

References